Hi all,
I've had this 914 for over 12 years now - bought by myself and my grandfather ( @JDW914 ) as a project back in 2011 - and used it regularly for a decade before a fire damaged a lot of the car's wiring and paint. It was re-restored 2 years ago, and hasn't run since, as we've had a lot of trouble getting it to stay running. I've finally taken full custody of the car and have been digging into trying to figure out this problem in earnest.
Where I stand:
The car is fully restored, and appears to be in strong working order. This is a nearly all-stock 1974 2.0 with an Original Customs 2056 upgrade. No other major changes.
- Compression checked at around an incredible 180# on all cylinders.
- Valve lash is at nominal on all valves.
- All fuel and vapor lines replaced with new.
- Fuel pump wiring replaced with 12AWG for more sturdiness, less resistance.
- Fuel pressure regulator replaced with new, added analog fuel pressure gauge in engine compartment.
- Fuel injectors (cause of the fire) were replaced with SMP FJ67s.
- Distributor cleaned and rebuilt, checked for responsiveness on ignition and FI points.
- All engine bay wiring has been replaced with brand new harnesses (and then meticulously rebuilt and checked for any issues after continued problems).
- Transmission ground replaced with brand new braided strap.
- The ECU (Type-044) (though somewhat charred) was tested by Specialized ECU Repair last year and given a clean bill of health.
- The MPS was replaced with a rebuilt unit correct for the car from a reputable community member.
- All minor engine sensors have been replaced with new and tested for correct responses.
- Throttle body and TPS rebuilt with new board, tested correct.
- Relay board was de-resin-ed, cleaned, and all joints were soldered, with all paths testing under 8Ω (seems a little high, but I guess that's just what solid copper gets you)
No matter what we've done, the car seems to die as soon as it's off the starter. It runs incredibly up until that point, then dies, but not immediately. Sprk continues, and it kind of sputters out. If spark is fairly retarded, it will sputter on for maybe 20 seconds before dying, which indicates spark is not an issue. And indeed, spark from a pulled wire stays strong to the very end.
However, it doesn't really respond any differently if starter fluid is sprayed into the intake manifold. This makes me think air mix might be an issue, but increasing air bleed seems to make it less eager to run rather than more. Additionally, The fuel pump is running, and the main injectors are most definitely firing, as the engine fires up every time, and the cold-start injector has been unplugged throughout my troubleshooting. The ECU has power on both pins 16 and 24.
2 other things do lead me to suspect some kind of fuel delivery issue, though: 1) The engine will run and stay running (BADLY and SMOKILY) with the CHT unplugged and open, and the spark VERY advanced. 2) When I move the throttle with the ignition on and engine off, I neither hear nor feel the injectors pulse.
Buuut, on the other hand, working the pedal while attempting to start the car normally will generally keep it alive longer, up to maybe 30 seconds, and pushing the car with ignition on, in gear gets a kick immediately upon spark, without running the starter circuit.
I intend to test the injectors by unplugging them and actuating the throttle to verify pulsing.
Does anyone have any advice on further tests to perform or ideas on failure modes this might be indicative of? Any sort of advice will be very, very appreciated.
This has been stumping myself, my grandpa, and every mechanic I've spoken with or had look at it for years, but I intend to figure it out.
Full Version: D-Jet 2.0 Runs and then Doesn't - Troubleshooting
Wow, a lot of info. Ok, here's the obligatory link for obligatory reading: https://members.rennlist.com/pbanders/ (assuming you haven't already seen that).
It does sound like a fuel mixture issue. My first thought was bad CHT or break in CHT wire, but it's strange that the car will run AT ALL with CHT unplugged. The components that have the biggest impact on fuel mixture and can enrichen it to the point of flooding are the CHT (again, unplugged, bad sensor, break in wire, etc.), the MPS (blown diaphragm, unplugged connector), and cold start valve (leaking). Focus on troubleshooting those components and their continuity back to the ECU. Somewhere in that link above is a pinout of the ECU so you can test continuity on the wiring harness to all the critical components.
Once the car starts and runs (briefly), will it do it again or do you have to wait for a while? Or is there any other evidence that you're flooding the engine (e.g., wet plugs, smell)? What's your fuel pressure reading?
You're not going to hear the injectors "pulse" or click with the ignition on and moving the throttle. They are triggered by, well, the trigger points connected to the back of the dizzy. What you should hear are clicks from the throttle position sensor as you move the throttle, but that's not critical. The car will run with the TPS, just not as well.
I'm sure the collective wisdom here will help you figure this out.
It does sound like a fuel mixture issue. My first thought was bad CHT or break in CHT wire, but it's strange that the car will run AT ALL with CHT unplugged. The components that have the biggest impact on fuel mixture and can enrichen it to the point of flooding are the CHT (again, unplugged, bad sensor, break in wire, etc.), the MPS (blown diaphragm, unplugged connector), and cold start valve (leaking). Focus on troubleshooting those components and their continuity back to the ECU. Somewhere in that link above is a pinout of the ECU so you can test continuity on the wiring harness to all the critical components.
Once the car starts and runs (briefly), will it do it again or do you have to wait for a while? Or is there any other evidence that you're flooding the engine (e.g., wet plugs, smell)? What's your fuel pressure reading?
You're not going to hear the injectors "pulse" or click with the ignition on and moving the throttle. They are triggered by, well, the trigger points connected to the back of the dizzy. What you should hear are clicks from the throttle position sensor as you move the throttle, but that's not critical. The car will run with the TPS, just not as well.
I'm sure the collective wisdom here will help you figure this out.
".......as soon as it is off the starter........"
Do you mean it starts and THEN when you release the KEY out of the STARTER-ENGAGE position it dies?
If so, in 1974 I had a 1970 1.7 that had this problem - ignition wire in the ignition switch was the culprit.
Hi all,
I've had this 914 for over 12 years now - bought by myself and my grandfather ( @JDW914 ) as a project back in 2011 - and used it regularly for a decade before a fire damaged a lot of the car's wiring and paint. It was re-restored 2 years ago, and hasn't run since, as we've had a lot of trouble getting it to stay running. I've finally taken full custody of the car and have been digging into trying to figure out this problem in earnest.
Where I stand:
The car is fully restored, and appears to be in strong working order. This is a nearly all-stock 1974 2.0 with an Original Customs 2056 upgrade. No other major changes.
- Compression checked at around an incredible 180# on all cylinders.
- Valve lash is at nominal on all valves.
- All fuel and vapor lines replaced with new.
- Fuel pump wiring replaced with 12AWG for more sturdiness, less resistance.
- Fuel pressure regulator replaced with new, added analog fuel pressure gauge in engine compartment.
- Fuel injectors (cause of the fire) were replaced with SMP FJ67s.
- Distributor cleaned and rebuilt, checked for responsiveness on ignition and FI points.
- All engine bay wiring has been replaced with brand new harnesses (and then meticulously rebuilt and checked for any issues after continued problems).
- Transmission ground replaced with brand new braided strap.
- The ECU (Type-044) (though somewhat charred) was tested by Specialized ECU Repair last year and given a clean bill of health.
- The MPS was replaced with a rebuilt unit correct for the car from a reputable community member.
- All minor engine sensors have been replaced with new and tested for correct responses.
- Throttle body and TPS rebuilt with new board, tested correct.
- Relay board was de-resin-ed, cleaned, and all joints were soldered, with all paths testing under 8Ω (seems a little high, but I guess that's just what solid copper gets you)
No matter what we've done, the car seems to die as soon as it's off the starter. It runs incredibly up until that point, then dies, but not immediately. Sprk continues, and it kind of sputters out. If spark is fairly retarded, it will sputter on for maybe 20 seconds before dying, which indicates spark is not an issue. And indeed, spark from a pulled wire stays strong to the very end.
However, it doesn't really respond any differently if starter fluid is sprayed into the intake manifold. This makes me think air mix might be an issue, but increasing air bleed seems to make it less eager to run rather than more. Additionally, The fuel pump is running, and the main injectors are most definitely firing, as the engine fires up every time, and the cold-start injector has been unplugged throughout my troubleshooting. The ECU has power on both pins 16 and 24.
2 other things do lead me to suspect some kind of fuel delivery issue, though: 1) The engine will run and stay running (BADLY and SMOKILY) with the CHT unplugged and open, and the spark VERY advanced. 2) When I move the throttle with the ignition on and engine off, I neither hear nor feel the injectors pulse.
Buuut, on the other hand, working the pedal while attempting to start the car normally will generally keep it alive longer, up to maybe 30 seconds, and pushing the car with ignition on, in gear gets a kick immediately upon spark, without running the starter circuit.
I intend to test the injectors by unplugging them and actuating the throttle to verify pulsing.
Does anyone have any advice on further tests to perform or ideas on failure modes this might be indicative of? Any sort of advice will be very, very appreciated.
This has been stumping myself, my grandpa, and every mechanic I've spoken with or had look at it for years, but I intend to figure it out.
Do you mean it starts and THEN when you release the KEY out of the STARTER-ENGAGE position it dies?
If so, in 1974 I had a 1970 1.7 that had this problem - ignition wire in the ignition switch was the culprit.
QUOTE(Cessnaporsche01 @ Jul 1 2023, 02:37 PM) 
Hi all,
I've had this 914 for over 12 years now - bought by myself and my grandfather ( @JDW914 ) as a project back in 2011 - and used it regularly for a decade before a fire damaged a lot of the car's wiring and paint. It was re-restored 2 years ago, and hasn't run since, as we've had a lot of trouble getting it to stay running. I've finally taken full custody of the car and have been digging into trying to figure out this problem in earnest.
Where I stand:
The car is fully restored, and appears to be in strong working order. This is a nearly all-stock 1974 2.0 with an Original Customs 2056 upgrade. No other major changes.
- Compression checked at around an incredible 180# on all cylinders.
- Valve lash is at nominal on all valves.
- All fuel and vapor lines replaced with new.
- Fuel pump wiring replaced with 12AWG for more sturdiness, less resistance.
- Fuel pressure regulator replaced with new, added analog fuel pressure gauge in engine compartment.
- Fuel injectors (cause of the fire) were replaced with SMP FJ67s.
- Distributor cleaned and rebuilt, checked for responsiveness on ignition and FI points.
- All engine bay wiring has been replaced with brand new harnesses (and then meticulously rebuilt and checked for any issues after continued problems).
- Transmission ground replaced with brand new braided strap.
- The ECU (Type-044) (though somewhat charred) was tested by Specialized ECU Repair last year and given a clean bill of health.
- The MPS was replaced with a rebuilt unit correct for the car from a reputable community member.
- All minor engine sensors have been replaced with new and tested for correct responses.
- Throttle body and TPS rebuilt with new board, tested correct.
- Relay board was de-resin-ed, cleaned, and all joints were soldered, with all paths testing under 8Ω (seems a little high, but I guess that's just what solid copper gets you)
No matter what we've done, the car seems to die as soon as it's off the starter. It runs incredibly up until that point, then dies, but not immediately. Sprk continues, and it kind of sputters out. If spark is fairly retarded, it will sputter on for maybe 20 seconds before dying, which indicates spark is not an issue. And indeed, spark from a pulled wire stays strong to the very end.
However, it doesn't really respond any differently if starter fluid is sprayed into the intake manifold. This makes me think air mix might be an issue, but increasing air bleed seems to make it less eager to run rather than more. Additionally, The fuel pump is running, and the main injectors are most definitely firing, as the engine fires up every time, and the cold-start injector has been unplugged throughout my troubleshooting. The ECU has power on both pins 16 and 24.
2 other things do lead me to suspect some kind of fuel delivery issue, though: 1) The engine will run and stay running (BADLY and SMOKILY) with the CHT unplugged and open, and the spark VERY advanced. 2) When I move the throttle with the ignition on and engine off, I neither hear nor feel the injectors pulse.
Buuut, on the other hand, working the pedal while attempting to start the car normally will generally keep it alive longer, up to maybe 30 seconds, and pushing the car with ignition on, in gear gets a kick immediately upon spark, without running the starter circuit.
I intend to test the injectors by unplugging them and actuating the throttle to verify pulsing.
Does anyone have any advice on further tests to perform or ideas on failure modes this might be indicative of? Any sort of advice will be very, very appreciated.
This has been stumping myself, my grandpa, and every mechanic I've spoken with or had look at it for years, but I intend to figure it out.
QUOTE(BeatNavy @ Jul 1 2023, 05:01 PM)
Wow, a lot of info. Ok, here's the obligatory link for obligatory reading: https://members.rennlist.com/pbanders/ (assuming you haven't already seen that).
It does sound like a fuel mixture issue. My first thought was bad CHT or break in CHT wire, but it's strange that the car will run AT ALL with CHT unplugged. The components that have the biggest impact on fuel mixture and can enrichen it to the point of flooding are the CHT (again, unplugged, bad sensor, break in wire, etc.), the MPS (blown diaphragm, unplugged connector), and cold start valve (leaking). Focus on troubleshooting those components and their continuity back to the ECU. Somewhere in that link above is a pinout of the ECU so you can test continuity on the wiring harness to all the critical components.
Once the car starts and runs (briefly), will it do it again or do you have to wait for a while? Or is there any other evidence that you're flooding the engine (e.g., wet plugs, smell)? What's your fuel pressure reading?
You're not going to hear the injectors "pulse" or click with the ignition on and moving the throttle. They are triggered by, well, the trigger points connected to the back of the dizzy. What you should hear are clicks from the throttle position sensor as you move the throttle, but that's not critical. The car will run with the TPS, just not as well.
I'm sure the collective wisdom here will help you figure this out.Thanks! I'm intimately familiar with Brad's awesome write-up.
I agree that it seems like mixture related, and the CHT situation is strange. I just went out and re-verified as it's been a while since I did it that the car will run with the CHT unplugged. Not only does it run, but it runs pretty well, if rich enough to send some visible brown fumes out. Very little responsiveness to throttle in that state, though, just sputtering when I try to rev it.
The ECU harness has been very thoroughly checked, but I think I'll be reevaluating the MPS. Failing that, I'm a bit untrusting of the injectors.
The car will start and die as many times as I ask it to. The plugs look hot, but wet, and pretty normal for how this car's plugs have always looked after use. It doesn't smell too fuel-y. Fuel pressure is 28psi on the dot, but I've taken it as high as 40psi trying to test if it would respond to more fuel and the behavior didn't change.
Good to know on the injector/TPS front - I think I'd been mislead in my understanding of some old posts here.
QUOTE(ctc911ctc @ Jul 1 2023, 05:18 PM)
".......as soon as it is off the starter........"
Do you mean it starts and THEN when you release the KEY out of the STARTER-ENGAGE position it dies?
If so, in 1974 I had a 1970 1.7 that had this problem - ignition wire in the ignition switch was the culprit.
Yes, but not so immediately, and spark does continue. I did think this could be the case for a while, but I've tested all the wires in the key/ignition circuit, and replaced the ignition switch with a brand new one with no change. While I was troubleshooting this, I also verified that the seatbelt relay bypass was still solid and not the source of my problems.
QUOTE(Cessnaporsche01 @ Jul 1 2023, 05:51 PM)
Good to know on the injector/TPS front - I think I'd been mislead in my understanding of some old posts here.
My mistake, been too long on Microsquirt. That IS the sound of the injector clicking. You were correct.
Were the injectors new when you purchased them? Have you flow tested them or checked for leaks? Wet plugs sounds like way too rich.
Distributor is 180* out, been there done that, several times.
Key in run position, does fuel pump run for 1.5 seconds?
Key in run position, is there 12 vdc at the positive terminal of the coil?
If yes, yes, run a jumper wire from battery to coil, positive side.
Will car now stay running?
Have you checked and validated the relay board? Those get bad.
Key in run position, is there 12 vdc at the positive terminal of the coil?
If yes, yes, run a jumper wire from battery to coil, positive side.
Will car now stay running?
Have you checked and validated the relay board? Those get bad.
QUOTE(mgphoto @ Jul 1 2023, 06:56 PM)
Distributor is 180* out, been there done that, several times.
I’m pretty sure if the distributor drive gear is installed correctly, it’s impossible to install the distributor off 180 degrees because the keyway is offset from center to prevent this on a type4
Another test I would do to rule out ignition (spark)
Jumper to coil, positive side.
Hand held starter button, so I can do it while reaching in the engine bay
Starter fluid ether.
While key is on.
Jumper on coil
You are now fuel…continuos spray into throttle body the starting fluid
Short test, keep it running with no starter.
If that works….you are onto the fuel system.
Jumper to coil, positive side.
Hand held starter button, so I can do it while reaching in the engine bay
Starter fluid ether.
While key is on.
Jumper on coil
You are now fuel…continuos spray into throttle body the starting fluid
Short test, keep it running with no starter.
If that works….you are onto the fuel system.
Fuel injector test
Get 4 small baby food glass jars (because they fit for this test)
Remove the 10mm nut on each injector
Pull the injectors out as a pair, place the ends into baby food jars so the jars will hold fuel (takes a little positioning, but it works fine)
Remove center wire on coil (remove from car, we don’t want a chance of a spark)
Turn over engine for 30-45 seconds
Go inspect each jar to observe the exact same amount of fuel
Get 4 small baby food glass jars (because they fit for this test)
Remove the 10mm nut on each injector
Pull the injectors out as a pair, place the ends into baby food jars so the jars will hold fuel (takes a little positioning, but it works fine)
Remove center wire on coil (remove from car, we don’t want a chance of a spark)
Turn over engine for 30-45 seconds
Go inspect each jar to observe the exact same amount of fuel
QUOTE(r_towle @ Jul 2 2023, 12:45 PM)
Fuel injector test
Get 4 small baby food glass jars (because they fit for this test)
Remove the 10mm nut on each injector
Pull the injectors out as a pair, place the ends into baby food jars so the jars will hold fuel (takes a little positioning, but it works fine)
Remove center wire on coil (remove from car, we don’t want a chance of a spark)
Turn over engine for 30-45 seconds
Go inspect each jar to observe the exact same amount of fuel
Excellent advise,certainly starved for fuel .
You’ve been through so much and apparently either overlooked something or it is intermittent. I would start from zero, trust no previous assumptions and be methodical. I have a couple djet test procedure lists on my Classics webpage, Tech Notebook tab, specifically the Kjell Nelin document. Go through that and you should find the issue.
I would check ignition timing. And even if it is correct bump it to 5 degrees more advance, just to see what happens. The distributor on one of my cars is worn and when it dropped back to full retard it would barely run. I had to adjust the stop (actually bend it) to keep enough advance at idle that it would run well.
Just a thought.
Just a thought.
A very easy, no work first test could be whether the mps holds vacuum.
QUOTE(r_towle @ Jul 1 2023, 04:37 PM)
QUOTE(mgphoto @ Jul 1 2023, 06:56 PM)
Distributor is 180* out, been there done that, several times.
I’m pretty sure if the distributor drive gear is installed correctly, it’s impossible to install the distributor off 180 degrees because the keyway is offset from center to prevent this on a type4
Haha
QUOTE
The MPS was replaced with a rebuilt unit correct for the car from a reputable community member.
If air fuel mixture is off- too rich or too lean to keep the car running, the MPS might the culprit.
I’m not perfectly sure, but when I searched for a vacuum leak one time I removed every hose from the plenum and the car runs and idles fine.
Not sure if you need the MPs for idle….or start
Not sure if you need the MPs for idle….or start
Lot of responses, so I'll make my way down the list.
Distributor is 180* out, been there done that, several times.
I’m pretty sure if the distributor drive gear is installed correctly, it’s impossible to install the distributor off 180 degrees because the keyway is offset from center to prevent this on a type4
Yeah, I've double and triple checked the timing and made sure the timing gear was aligned correctly, as that was my first assumption based on the weird behavior.
Key in run position, does fuel pump run for 1.5 seconds?
Key in run position, is there 12 vdc at the positive terminal of the coil?
If yes, yes, run a jumper wire from battery to coil, positive side.
Will car now stay running?
Have you checked and validated the relay board? Those get bad.
Fuel pump does prime, and there is 12V at the coil when the ignition is on. I did still try running a jumper wire, but no effect on the engine behavior, so I'm still thinking it's not spark.
I did just go through the relay board last week - full rebuild and 100% check (as mentioned in the OP).
Another test I would do to rule out ignition (spark)
Jumper to coil, positive side.
Hand held starter button, so I can do it while reaching in the engine bay
Starter fluid ether.
While key is on.
Jumper on coil
You are now fuel…continuos spray into throttle body the starting fluid
Short test, keep it running with no starter.
If that works….you are onto the fuel system.
This does work. So reinforcing almost certainly fuel delivery is the issue.
Fuel injector test
Get 4 small baby food glass jars (because they fit for this test)
Remove the 10mm nut on each injector
Pull the injectors out as a pair, place the ends into baby food jars so the jars will hold fuel (takes a little positioning, but it works fine)
Remove center wire on coil (remove from car, we don’t want a chance of a spark)
Turn over engine for 30-45 seconds
Go inspect each jar to observe the exact same amount of fuel
Excellent advise,certainly starved for fuel .
Working on this one. Will update when I've got results.
You’ve been through so much and apparently either overlooked something or it is intermittent. I would start from zero, trust no previous assumptions and be methodical. I have a couple djet test procedure lists on my Classics webpage, Tech Notebook tab, specifically the Kjell Nelin document. Go through that and you should find the issue.
Thank, Jeff. That's more or less what I'm in the process of at the moment. I'll definitely read through the Nelin PDF.
I would check ignition timing. And even if it is correct bump it to 5 degrees more advance, just to see what happens. The distributor on one of my cars is worn and when it dropped back to full retard it would barely run. I had to adjust the stop (actually bend it) to keep enough advance at idle that it would run well.
Just a thought.
I've played with this quite a lot, and timing does improve the run time, but nowhere in the entire ~70 degree sweep I can access does it keep the car running, which is a stark contrast to how easily it will run at most any timing under ordinary circumstances.
If air fuel mixture is off- too rich or too lean to keep the car running, the MPS might the culprit.
I'm starting to lean strongly in this direction. I'm definitely going to try to test the MPS next - make sure it holds vacuum and if I can get readings on it. The car had run twice with all the current parts, before starting this behavior, but I wonder if the MPS could have failed.
QUOTE(r_towle @ Jul 1 2023, 07:37 PM)
QUOTE(mgphoto @ Jul 1 2023, 06:56 PM)
Distributor is 180* out, been there done that, several times.
I’m pretty sure if the distributor drive gear is installed correctly, it’s impossible to install the distributor off 180 degrees because the keyway is offset from center to prevent this on a type4
Yeah, I've double and triple checked the timing and made sure the timing gear was aligned correctly, as that was my first assumption based on the weird behavior.
QUOTE(r_towle @ Jul 1 2023, 07:35 PM)
Key in run position, does fuel pump run for 1.5 seconds?
Key in run position, is there 12 vdc at the positive terminal of the coil?
If yes, yes, run a jumper wire from battery to coil, positive side.
Will car now stay running?
Have you checked and validated the relay board? Those get bad.
Fuel pump does prime, and there is 12V at the coil when the ignition is on. I did still try running a jumper wire, but no effect on the engine behavior, so I'm still thinking it's not spark.
I did just go through the relay board last week - full rebuild and 100% check (as mentioned in the OP).
QUOTE(r_towle @ Jul 1 2023, 07:41 PM)
Another test I would do to rule out ignition (spark)
Jumper to coil, positive side.
Hand held starter button, so I can do it while reaching in the engine bay
Starter fluid ether.
While key is on.
Jumper on coil
You are now fuel…continuos spray into throttle body the starting fluid
Short test, keep it running with no starter.
If that works….you are onto the fuel system.
This does work. So reinforcing almost certainly fuel delivery is the issue.
QUOTE(porschetub @ Jul 1 2023, 07:56 PM)
QUOTE(r_towle @ Jul 2 2023, 12:45 PM)
Fuel injector test
Get 4 small baby food glass jars (because they fit for this test)
Remove the 10mm nut on each injector
Pull the injectors out as a pair, place the ends into baby food jars so the jars will hold fuel (takes a little positioning, but it works fine)
Remove center wire on coil (remove from car, we don’t want a chance of a spark)
Turn over engine for 30-45 seconds
Go inspect each jar to observe the exact same amount of fuel
Excellent advise,certainly starved for fuel .
Working on this one. Will update when I've got results.
QUOTE(JeffBowlsby @ Jul 1 2023, 09:06 PM)
You’ve been through so much and apparently either overlooked something or it is intermittent. I would start from zero, trust no previous assumptions and be methodical. I have a couple djet test procedure lists on my Classics webpage, Tech Notebook tab, specifically the Kjell Nelin document. Go through that and you should find the issue.
Thank, Jeff. That's more or less what I'm in the process of at the moment. I'll definitely read through the Nelin PDF.
QUOTE(bobboinski @ Jul 1 2023, 09:34 PM)
I would check ignition timing. And even if it is correct bump it to 5 degrees more advance, just to see what happens. The distributor on one of my cars is worn and when it dropped back to full retard it would barely run. I had to adjust the stop (actually bend it) to keep enough advance at idle that it would run well.
Just a thought.
I've played with this quite a lot, and timing does improve the run time, but nowhere in the entire ~70 degree sweep I can access does it keep the car running, which is a stark contrast to how easily it will run at most any timing under ordinary circumstances.
QUOTE(rjames @ Jul 2 2023, 02:18 AM)
QUOTE
The MPS was replaced with a rebuilt unit correct for the car from a reputable community member.
If air fuel mixture is off- too rich or too lean to keep the car running, the MPS might the culprit.
I'm starting to lean strongly in this direction. I'm definitely going to try to test the MPS next - make sure it holds vacuum and if I can get readings on it. The car had run twice with all the current parts, before starting this behavior, but I wonder if the MPS could have failed.
MPs, FI trigger points, CHT, tps
They all determine when and how much fuel.
First test is to make sure all injectors fire ( baby food jars)
That eliminate FI trigger points and wiring
CHT is easy, use a meter
TPS is also a meter and visual.
MPs, initial test is remove hose, suck on end, will it stick to your tongue
If you must use a tool , very little vacuum or you will break the MPs
If you want, I will ship you the inline djet tester to help you sort it out….but a volt/ohm meter will get you there too
They all determine when and how much fuel.
First test is to make sure all injectors fire ( baby food jars)
That eliminate FI trigger points and wiring
CHT is easy, use a meter
TPS is also a meter and visual.
MPs, initial test is remove hose, suck on end, will it stick to your tongue
If you must use a tool , very little vacuum or you will break the MPs
If you want, I will ship you the inline djet tester to help you sort it out….but a volt/ohm meter will get you there too
If you are certain that ignition is not the issue then it has to be fuel delivery. You need to determine if it's fuel starvation or flooding, and then go from there. It can be surprisingly difficult to do that, I get it, but the suspects are different depending on the situation. Without a broad idea of what's going on you can't focus on likeliest of causes.
I'd consider doing the injectors-in-jars test to see if you're getting fuel delivery reliably and roughly equally at each injector. EDIT: Rich beat me to it.
I'd consider doing the injectors-in-jars test to see if you're getting fuel delivery reliably and roughly equally at each injector. EDIT: Rich beat me to it.
Ooo, flooding.
I did have one of my cold start injectors die wide open
Took a while to figure that one out.
Route around it with a brass fitting will take it out of play fir diagnostics.
Not sure if those are available now, they were not back when I had issues.
I did have one of my cold start injectors die wide open
Took a while to figure that one out.
Route around it with a brass fitting will take it out of play fir diagnostics.
Not sure if those are available now, they were not back when I had issues.
Okay, did the baby-food-jar-test. All injectors are firing and equal. got about a tablespoon of fuel from 30s of cranking in each jar.
CHT tests at about 3.1kΩ at what should be ~85°F which seems appropriate.
TPS engages all circuits correctly, as far as I can tell, and like I said, the board is a shiny new 914rubber one.
MPS holds a vacuum in the suck test, but that's all I know so far.
I'm pretty sure that the engine is in a fuel-starved state, since it runs okayish with the CHT unplugged. And I've been doing all testing with the cold-start-valve unplugged and the hose to it clamped off, just in case (although that valve is brand new too).
CHT tests at about 3.1kΩ at what should be ~85°F which seems appropriate.
TPS engages all circuits correctly, as far as I can tell, and like I said, the board is a shiny new 914rubber one.
MPS holds a vacuum in the suck test, but that's all I know so far.
I'm pretty sure that the engine is in a fuel-starved state, since it runs okayish with the CHT unplugged. And I've been doing all testing with the cold-start-valve unplugged and the hose to it clamped off, just in case (although that valve is brand new too).
Test the MPS: https://members.rennlist.com/pbanders/manif...S%20Diagnostics
You're somewhat convinced that it's fuel starved. I'm not sure I am, but you're standing in front of it. That resistance value on the CHT seems high. Based on Anders' numbers he has the 0 280 130 012 CHT (correct for '74) at around 2.5 k at 68 degrees.
Here's another reference point on the 012 CHT: http://www.914world.com/bbs2/index.php?showtopic=351065
The curve is not linear.
You're somewhat convinced that it's fuel starved. I'm not sure I am, but you're standing in front of it. That resistance value on the CHT seems high. Based on Anders' numbers he has the 0 280 130 012 CHT (correct for '74) at around 2.5 k at 68 degrees.
Here's another reference point on the 012 CHT: http://www.914world.com/bbs2/index.php?showtopic=351065
The curve is not linear.
What is your dwell?
Post a picture from above with your distributor in clear focus
Post a picture from above with your distributor in clear focus
And beat navy is on a good thread
OP states car run longer but crappy when CHT is unplugged
CHT might be junk
OP states car run longer but crappy when CHT is unplugged
CHT might be junk
You could be right, BeatNavy. I may order another CHT sensor since they're cheap. I'll pull mine and test it directly from tail to sensor body to be sure first. I'm going to try and find a vacuum pump to test the MPS too.
And here you go, r_towle:
And one correction on your last post - it doesn't "run longer" with no CHT, it runs indefinitely. It needs a lot of advance, since obviously it's on the edge of flooding at maximum pulse width, and it doesn't like throttle movement, but it will sit and run until I shut it off. I'd actually taken it for a short, stuttering drive in this state last year to move it.
And here you go, r_towle:
And one correction on your last post - it doesn't "run longer" with no CHT, it runs indefinitely. It needs a lot of advance, since obviously it's on the edge of flooding at maximum pulse width, and it doesn't like throttle movement, but it will sit and run until I shut it off. I'd actually taken it for a short, stuttering drive in this state last year to move it.
Sorry that image is huge - I don't know how to resize image previews in BBS - oops
QUOTE(Cessnaporsche01 @ Jul 2 2023, 04:03 PM)
You could be right, BeatNavy. I may order another CHT sensor since they're cheap. I'll pull mine and test it directly from tail to sensor body to be sure first. I'm going to try and find a vacuum pump to test the MPS too.
And here you go, r_towle:
And one correction on your last post - it doesn't "run longer" with no CHT, it runs indefinitely. It needs a lot of advance, since obviously it's on the edge of flooding at maximum pulse width, and it doesn't like throttle movement, but it will sit and run until I shut it off. I'd actually taken it for a short, stuttering drive in this state last year to move it.
You can use a variable potentiometer in place of the CHT sender. If that cures it install the new CHT sensor. If it doesn't run quite as well with the new sensor re-install the potentiometer, dial it in where the engine runs the best then remove it and check the ohm value across the potentiometer. Then install an in line resistor of that value.
Put the cap back on.
Back up
Take a pic of the top of the engine so we can see the position of the distributor in relation to the engine and fan etc
Back up
Take a pic of the top of the engine so we can see the position of the distributor in relation to the engine and fan etc
And yes, a potentiometer (radio shack is no more, so sad) which is a volume knob/switch, inline with your CHT.
Tune and turn…once perfect you can measure the resistance across the potentiometer then buy and install a resistor in its place.
I did this with a “larger than stock” engine running djet.
It required an 02 sensor , driving and turning the knob until I got it perfect.
While yo u might need it, you may also just need a new one.
Djet tends to run pretty darn rich.
Tune and turn…once perfect you can measure the resistance across the potentiometer then buy and install a resistor in its place.
I did this with a “larger than stock” engine running djet.
It required an 02 sensor , driving and turning the knob until I got it perfect.
While yo u might need it, you may also just need a new one.
Djet tends to run pretty darn rich.
Here's the installed distributor, loosely in the correct orientation.
I was able to test vacuum and coil resistance of my MPS, and both seem good, but I don't currently have an inductance meter. Are failed cells likely to cause my symptoms?
And the '043 MPS matches the '044 ECU, right? I think I'm reading Brad's chart correctly.
I was also able to test variable resistance on the CHT. There were no potentiometers readily available (RIP Radio Shack) but I was able to get a bunch of 1kΩ resistors from Micro Center. I unplugged the CHT and soldered together a daisy chain of resistors and clipped them to the battery ground. I then patched the CHT connector from the engine wiring harness to the daisy chain with an alligator clip and wire to create a rudimentary potentiometer.
The engine would not stay started until I hit 6kΩ of resistance, and was making a lot of dark smoke like it does with the CHT unplugged. Moving the cable to 5, then 4kΩ kept it running and changed its demeanor pretty substantially. RPMs picked up fast, and it began backfiring into the intake, so i pulled some timing out. After a minute or so, I was able to bring it down to 3, then 2, then 1kΩ and keep it running (at no point in this entire process thus far did the throttle leave the idle position). It was still smoking heavily at 1kΩ, and even with as much retarding as it would take, would backfire maybe once every 5 seconds or so, and was sitting at what sounded to my ear like 2-3k rpm. I tested throttle response, which was very slow (>1s) and extreme (engine screamed at a light blip of the throttle).
I may have to test with smaller resistors below 1kΩ, as it's clearly still extremely rich at that point. And I think spark is too far advanced, although it dies outright if I pull it any further back. Dizzy weights are actuating freely.
sounds too rich.
Not sure why, but I would start at the beginning, check the fuel system, and check why the sensors are telling the ECU to send more fuel, or longer duration of fuel.
When I had this type of issue, my first one was CHT, my second was a bad MPS (thing barely starts) and my third was the Cold Start injector was dead, yet in the wide open position.
Vacuum leaks will also ruin any troubleshooting you are doing.
the hidden ones are
plenum cracks and leaks under the bottom in the metal.
Plenum to Intake runner hoses are finally toast and no longer seal
Intake manifold gasket to head is toast.
Fuel injector little rubber seals at the tip
AAR corroded internally, now leaking
I disconnect all vacuum lines from the plenum to test...
you need to hunt the three
Air (measured air only allowed...so no leaks)
Spark (is the distributor working as designed...might be having internal issues)
Fuel...too much...and why
Not sure why, but I would start at the beginning, check the fuel system, and check why the sensors are telling the ECU to send more fuel, or longer duration of fuel.
When I had this type of issue, my first one was CHT, my second was a bad MPS (thing barely starts) and my third was the Cold Start injector was dead, yet in the wide open position.
Vacuum leaks will also ruin any troubleshooting you are doing.
the hidden ones are
plenum cracks and leaks under the bottom in the metal.
Plenum to Intake runner hoses are finally toast and no longer seal
Intake manifold gasket to head is toast.
Fuel injector little rubber seals at the tip
AAR corroded internally, now leaking
I disconnect all vacuum lines from the plenum to test...
you need to hunt the three
Air (measured air only allowed...so no leaks)
Spark (is the distributor working as designed...might be having internal issues)
Fuel...too much...and why
I definitely agree on the richness. And good point of potential vacuum leaks. All the hoses and seals are fresh, so it should be pretty buttoned up, but it's certainly worth checking for anything that isn't.
I can definitely rule out AAR and CSV since both are clamped off, and while I suspect the CHT is only exacerbating the symptoms of the real issue, I do have a new one to install that seems more in-spec than the current one. I think I'll check MPS inductance too, to be totally sure since, if I understand correctly, that's what the ECU is reading.
I can definitely rule out AAR and CSV since both are clamped off, and while I suspect the CHT is only exacerbating the symptoms of the real issue, I do have a new one to install that seems more in-spec than the current one. I think I'll check MPS inductance too, to be totally sure since, if I understand correctly, that's what the ECU is reading.
Finding vacuum leaks is always a good idea, although unless it's related to vacuum directly to or on the MPS I don't think that's your root cause.
Yes, I believe your MPS/ECU combo is "approved" (I agree, I've always found that table layout confusing). An inductance meter is required to check that the aneroid cells have not failed and/or check the values sent to the ECU. You have a repaired MPS, correct? I suppose it's possible that the tune it totally out of whack or maybe it was never verified after repair.
So if the jury thinks "rich it is" (including Rich
) then (copying from Anders):
Manifold pressure sensor - vacuum leak in sensor (cracked diaphragm), failed aneroid cell, vacuum hose to plenum leaky or detatched
Fuel pressure - too high, clogged fuel return line
Injectors - wrong injector for application, stuck open or leaky injector
Cold start valve - stuck open or leaky
Low manifold vacuum - due to either engine wear or non-stock cam, overly-tight valve adjustment
Intake Air Temperature Sensor - missing or open sensor
Cylinder Head Temperature Sensor - open in either the sensor or in the wiring harness or connector, failed sensor (stuck at high resistance value), wrong sensor for application
Trigger Contacts - worn/bouncing contacts causing additional injection pulses
ECU - component failure in ECU
I've crossed out the ones you have definitively ruled out. it's also not likely to be intake air temp sensor as that has a relatively low impact on mixture.
I have a spare 043 MPS (I believe) that should be functional for testing purposes. I believe I have a spare 044 ECU as well. You can borrow both for testing purposes if that helps. I'd need a day or two to find and ship.
Yes, I believe your MPS/ECU combo is "approved" (I agree, I've always found that table layout confusing). An inductance meter is required to check that the aneroid cells have not failed and/or check the values sent to the ECU. You have a repaired MPS, correct? I suppose it's possible that the tune it totally out of whack or maybe it was never verified after repair.
So if the jury thinks "rich it is" (including Rich
) then (copying from Anders):Manifold pressure sensor - vacuum leak in sensor (cracked diaphragm), failed aneroid cell, vacuum hose to plenum leaky or detatched
Injectors - wrong injector for application, stuck open or leaky injector
Low manifold vacuum - due to either engine wear or non-stock cam, overly-tight valve adjustment
Intake Air Temperature Sensor - missing or open sensor
Cylinder Head Temperature Sensor - open in either the sensor or in the wiring harness or connector, failed sensor (stuck at high resistance value), wrong sensor for application
Trigger Contacts - worn/bouncing contacts causing additional injection pulses
ECU - component failure in ECU
I've crossed out the ones you have definitively ruled out. it's also not likely to be intake air temp sensor as that has a relatively low impact on mixture.
I have a spare 043 MPS (I believe) that should be functional for testing purposes. I believe I have a spare 044 ECU as well. You can borrow both for testing purposes if that helps. I'd need a day or two to find and ship.
Who rebuilt the MPs?
What diaphragm was used?
The diaphragm needs tuning to get it right, and it’s most likely a different material than the original metal, so the original setting will be wrong.
What diaphragm was used?
The diaphragm needs tuning to get it right, and it’s most likely a different material than the original metal, so the original setting will be wrong.
The MPS I have came from Rich Bontempi's High Performance House. Don't know what diaphragm was used, but I assume it was one matched to the original spec. It is not the MPS from my car, as that one became fully encased in melted plastic from the battery/hoses during our fire, and wasn't salvageable.
As for the remaining, I'll start with manifold vacuum, since that should be a good start to determining if there are any leaks (or other complications as noted). Should be, like, 15-20 inHg with the throttle closed, yes?
I may take you up on the offer of that spare MPS/ECU for testing, BeatNavy - that'd be much appreciated, but I'll hold off for the moment until I've got the new CHT in, and checked through potential vacuum issues.
As for the remaining, I'll start with manifold vacuum, since that should be a good start to determining if there are any leaks (or other complications as noted). Should be, like, 15-20 inHg with the throttle closed, yes?
I may take you up on the offer of that spare MPS/ECU for testing, BeatNavy - that'd be much appreciated, but I'll hold off for the moment until I've got the new CHT in, and checked through potential vacuum issues.
Does your mps have Chris Foley's adjustable screws in it?
My manifold vacuum at idle is 21-23.
The kit from Tangerine racing is excellent if you want to be able to tune your mps.
My manifold vacuum at idle is 21-23.
The kit from Tangerine racing is excellent if you want to be able to tune your mps.
QUOTE(Cessnaporsche01 @ Jul 7 2023, 10:31 AM)
The MPS I have came from Rich Bontempi's High Performance House. Don't know what diaphragm was used, but I assume it was one matched to the original spec. It is not the MPS from my car, as that one became fully encased in melted plastic from the battery/hoses during our fire, and wasn't salvageable.
As for the remaining, I'll start with manifold vacuum, since that should be a good start to determining if there are any leaks (or other complications as noted). Should be, like, 15-20 inHg with the throttle closed, yes?
I may take you up on the offer of that spare MPS/ECU for testing, BeatNavy - that'd be much appreciated, but I'll hold off for the moment until I've got the new CHT in, and checked through potential vacuum issues.
So, unless it is a tested used MPS...it has a different diaphragm.
This might be the last test I would do.
The diaphragm from the OEM MPS is made from Beryllium which is now outlawed....
the new diaphragms were made up in (at least what I can recall) two or three batches.
Foley had a setup, he tested it, and it was darn close to the same response.
Regardless.
If it holds vacuum....
If you can test your AF ratio with an 02 sensor.
I would suggest loosening the nut, allen etc...
I did this years ago...its not super hard, nor is it super accurate.
I think the ECU has something like 4-5 AF maps...that is all.
MPS tells it which one to use for a specific condition.
This is not modern EFI where you can tune it really accurately.
Nope...its "get it in the ballpark" and run it a bit rich to maintain a cool running engine.
It will never be accurate...but it does get close.
Intentionally rich by design.
I got an 02 sensor (its an airline gauge) sold many places.
I wired it up to 10-15 feet of trailer wire.
02 sensor goes in tailpipe, hooked to a coat hanger...held in however you can make it work.
Wires over top of car, held with tape.
Gauge so I can see it while driving
Wrench and Allen wrench with me.
Takes about 45 minutes (drive, pull over, change MPS, drive) to learn which direction you need to go...then to tune it properly for your engine and elevation.
lets just say that Djet, properly tuned, can do 2.4 liters.
Its not a hack...but without a dyne...drive and tune works.
the more you do it, the more accurate you get (again...its not worth the extra effort of EGT sensors or a permanent O2....because its never accurate)
You want to get into the right base settings..and the system will toggle between all the hard coded AF maps it has, which is really not too many.
Fine tuning for race day is a potentiometer on the CHT...go to 11.
Depending upon how much you love math...
The (any) 02 sensor delivers a very small range....so its something hard to read unless you have a good gauge.
Otherwise...you can read it from a digital meter...and do math while driving and tuning (not my idea of fun)
I just got an analog gauge...I can see it.
Left turn makes gauge go this way..right turn goes this way.
All temporary because you will never change this setting ever again.
BUT...that may not be your problem...
so again...I would wait until the end, validate and test the rest of the list of things.
Its not super hard to test all the parts.
Again..I am more than happy to ship you the official Bosch Djet tester to get you through it...or...its all multimeter.
rich
Which tester do you have Rich?
QUOTE(r_towle @ Jul 6 2023, 07:08 PM)
sounds too rich.
Not sure why, but I would start at the beginning, check the fuel system, and check why the sensors are telling the ECU to send more fuel, or longer duration of fuel.
When I had this type of issue, my first one was CHT, my second was a bad MPS (thing barely starts) and my third was the Cold Start injector was dead, yet in the wide open position.
Vacuum leaks will also ruin any troubleshooting you are doing.
the hidden ones are
plenum cracks and leaks under the bottom in the metal.
Plenum to Intake runner hoses are finally toast and no longer seal
Intake manifold gasket to head is toast.
Fuel injector little rubber seals at the tip
AAR corroded internally, now leaking
I disconnect all vacuum lines from the plenum to test...
you need to hunt the three
Air (measured air only allowed...so no leaks)
Spark (is the distributor working as designed...might be having internal issues)
Fuel...too much...and why
If the Plenum is leaky, everything seems suspect. It is the foundation of the system. It must be able to hold a vacuum
Ask me how I know......
QUOTE(Cessnaporsche01 @ Jul 7 2023, 10:31 AM)
As for the remaining, I'll start with manifold vacuum, since that should be a good start to determining if there are any leaks (or other complications as noted). Should be, like, 15-20 inHg with the throttle closed, yes?
I believe that is roughly correct, although the decel valve (assuming it's present) will open anywhere from 18 to 21 inHg and relieve the vacuum. 15 inHg at idle is sufficient.
QUOTE(Cessnaporsche01 @ Jul 7 2023, 10:31 AM)
I may take you up on the offer of that spare MPS/ECU for testing, BeatNavy - that'd be much appreciated, but I'll hold off for the moment until I've got the new CHT in, and checked through potential vacuum issues.
Good plan
Leaks on djet just make it idle higher. Unless it's the mps diaphragm of course. Is your idle above 1k?
QUOTE(JeffBowlsby @ Jul 7 2023, 11:25 AM)
Which tester do you have Rich?
Ya know....after having read this thread a couple of times when you say that the engine runs with the CHT unplugged. What does that mean?
Does that mean that you unplug it and ground it?
On D-jet if you unplug that lead and it is not grounded....the engine should not run...period.
IF if it ungrounded and still runs...that points to something electrical like a shorted ECU...mistmatched ECU or faulty harness or connector somewhere in the circuit trace.
Does that mean that you unplug it and ground it?
On D-jet if you unplug that lead and it is not grounded....the engine should not run...period.
IF if it ungrounded and still runs...that points to something electrical like a shorted ECU...mistmatched ECU or faulty harness or connector somewhere in the circuit trace.
QUOTE(914_teener @ Jul 7 2023, 02:36 PM)
On D-jet if you unplug that lead and it is not grounded....the engine should not run...period.
That's been my experience as well, Rob, so I admit that did or does complicate it for me.
or...wiring harness is broken and it is indeed grounded
Im a fan of punt...get a new harness from Jeff.
its much faster, easier...and all the rubber boots are then present and in good shape.
having just moved one around...the boots can just fall apart in your fingers.
its much faster, easier...and all the rubber boots are then present and in good shape.
having just moved one around...the boots can just fall apart in your fingers.
QUOTE(Cessnaporsche01 @ Jul 2 2023, 12:20 PM)
Lot of responses, so I'll make my way down the list.
QUOTE(r_towle @ Jul 1 2023, 07:37 PM)
QUOTE(mgphoto @ Jul 1 2023, 06:56 PM)
Distributor is 180* out, been there done that, several times.
I’m pretty sure if the distributor drive gear is installed correctly, it’s impossible to install the distributor off 180 degrees because the keyway is offset from center to prevent this on a type4
Yeah, I've double and triple checked the timing and made sure the timing gear was aligned correctly, as that was my first assumption based on the weird behavior.
QUOTE(r_towle @ Jul 1 2023, 07:35 PM)
Key in run position, does fuel pump run for 1.5 seconds?
Key in run position, is there 12 vdc at the positive terminal of the coil?
If yes, yes, run a jumper wire from battery to coil, positive side.
Will car now stay running?
Have you checked and validated the relay board? Those get bad.
Fuel pump does prime, and there is 12V at the coil when the ignition is on. I did still try running a jumper wire, but no effect on the engine behavior, so I'm still thinking it's not spark.
I did just go through the relay board last week - full rebuild and 100% check (as mentioned in the OP).
QUOTE(r_towle @ Jul 1 2023, 07:41 PM)
Another test I would do to rule out ignition (spark)
Jumper to coil, positive side.
Hand held starter button, so I can do it while reaching in the engine bay
Starter fluid ether.
While key is on.
Jumper on coil
You are now fuel…continuos spray into throttle body the starting fluid
Short test, keep it running with no starter.
If that works….you are onto the fuel system.
This does work. So reinforcing almost certainly fuel delivery is the issue.
QUOTE(porschetub @ Jul 1 2023, 07:56 PM)
QUOTE(r_towle @ Jul 2 2023, 12:45 PM)
Fuel injector test
Get 4 small baby food glass jars (because they fit for this test)
Remove the 10mm nut on each injector
Pull the injectors out as a pair, place the ends into baby food jars so the jars will hold fuel (takes a little positioning, but it works fine)
Remove center wire on coil (remove from car, we don’t want a chance of a spark)
Turn over engine for 30-45 seconds
Go inspect each jar to observe the exact same amount of fuel
Excellent advise,certainly starved for fuel .
Working on this one. Will update when I've got results.
QUOTE(JeffBowlsby @ Jul 1 2023, 09:06 PM)
You’ve been through so much and apparently either overlooked something or it is intermittent. I would start from zero, trust no previous assumptions and be methodical. I have a couple djet test procedure lists on my Classics webpage, Tech Notebook tab, specifically the Kjell Nelin document. Go through that and you should find the issue.
Thank, Jeff. That's more or less what I'm in the process of at the moment. I'll definitely read through the Nelin PDF.
QUOTE(bobboinski @ Jul 1 2023, 09:34 PM)
I would check ignition timing. And even if it is correct bump it to 5 degrees more advance, just to see what happens. The distributor on one of my cars is worn and when it dropped back to full retard it would barely run. I had to adjust the stop (actually bend it) to keep enough advance at idle that it would run well.
Just a thought.
I've played with this quite a lot, and timing does improve the run time, but nowhere in the entire ~70 degree sweep I can access does it keep the car running, which is a stark contrast to how easily it will run at most any timing under ordinary circumstances.
QUOTE(rjames @ Jul 2 2023, 02:18 AM)
QUOTE
The MPS was replaced with a rebuilt unit correct for the car from a reputable community member.
If air fuel mixture is off- too rich or too lean to keep the car running, the MPS might the culprit.
I'm starting to lean strongly in this direction. I'm definitely going to try to test the MPS next - make sure it holds vacuum and if I can get readings on it. The car had run twice with all the current parts, before starting this behavior, but I wonder if the MPS could have failed.
If it holds vacuum that doesn’t mean you can omit the MPS as the culprit. As it’s been rebuilt it would be a miracle if it didn’t need calibrating for your engine. Doesn’t take more than a full turn of the inner screw either way to make it too rich or too lean. Get the adjustment tools from Tangerine.
Waiting on the LCR tester tool to test the MPS - didn't get the chance to check for vacuum leaks over the weekend so that's pending.
Just popping in to clarify since I hadn't considered the alternative interpretation around the CHT:
I am fully unplugging it - the CHT circuit on the engine harness is OPEN entirely; no shorts, no connection, infinite resistance. In this state, the engine is (as far as I understand) maximizing injector pulse-width. It is rich enough to blow a brown haze and require a bunch of ignition advance, but far from flooded.
This is why I worked my way down with resistors from 8kΩ, about double the maximum CHT value, and worked my way down until the engine died
**I should also note: The harness on this engine is a new one from Jeff as is. I tore it apart and rebuilt it from the ground up last year because I couldn't find a cause for this weird behavior and thought it might have an intermittent short or incorrect routing or something, but no change. However, as a result, I can verify with as much confidence as possible that the harness is good, correct, and in solid shape.
Just popping in to clarify since I hadn't considered the alternative interpretation around the CHT:
I am fully unplugging it - the CHT circuit on the engine harness is OPEN entirely; no shorts, no connection, infinite resistance. In this state, the engine is (as far as I understand) maximizing injector pulse-width. It is rich enough to blow a brown haze and require a bunch of ignition advance, but far from flooded.
This is why I worked my way down with resistors from 8kΩ, about double the maximum CHT value, and worked my way down until the engine died
**I should also note: The harness on this engine is a new one from Jeff as is. I tore it apart and rebuilt it from the ground up last year because I couldn't find a cause for this weird behavior and thought it might have an intermittent short or incorrect routing or something, but no change. However, as a result, I can verify with as much confidence as possible that the harness is good, correct, and in solid shape.
This is a "lo-fi" version of our main content. To view the full version with more information, formatting and images, please click here.