Last summer all of a sudden my car wouldn’t stay running. If I could get it started the idle would hunt and the car would die unless I kept on the gas. Lack of power at times. All somewhat erratic.
Found that the MPS wouldn’t hold vacuum.
Replaced the bad mps with a known good one. Car idles high when cold (higher than I think it should ~1600 rpm) so AAR is good, then when it warms up idle hunts from ~900rpm to the point where it almost dies unless I open the throttle body bleed screw quite a bit and turn the ECU knob just a few clicks away from full clockwise.
So I did the following hoping to fix the issue:
Replaced all vac hoses including intake runner to plenum hoses.
New intakecrunner gaskets
Verified plenum isn’t leaking
New throttle body gasket
Installed NOS throttle body
Rebuilt the distributor
Rebuilt injectors and flow tested
New fuel lines
Fuel pump is less than 2 years old
Set timing and dwell with advance disconnected
New CHT (resistance reads 1.7 w/engine off @70 degrees in the garage)
Calibrated the TPS, even unplugged it to take it out of the equation, didn’t change anything.
ECU matches the MPS (both correct part #s for a ‘75 2.0)
Tried a known good ECU from a ‘74, no change.
Feels like the MPS needs to be calibrated...but then again, these are all the same symptoms I had with the old bad mps. Replacement mps is from a Jeff B and was tested, but I haven’t retested it to see if it’s holding vacuum.
(Don’t have the necessary tool, but maybe that’s the next step)
Help! What am I missing?
Just a note on "known good MPS"...I was having terrible driveability problems with my '74 2L, similar to yours, and tried pretty much everything. Tested the MPS and it held a vacuum. I was stumped.
I was lamenting my probs when the guys at Tangerine said, "rebuild the MPS". "It's holding a vacuum" I replied. "Rebuild the MPS". So I gave them the MPS to rebuild.
It transformed the car. Car drives great now.
Turns out the diaphragm was cracked (Chris showed it to me) but somehow it was holding a vacuum anyway. Oh well.
Based on hunting idle it sounds like you're running too lean. That would be first suspect, but you should try to identify the broad root cause and then narrow down from there. What can you do to test if it's fuel delivery (too lean or too rich) and not something else like ignition, charging system, or vacuum? I assume you don't have a wideband O2 sensor. Have you tried unplugging the T1 (ambient air) sensor to see if that has an effect?
You've done a lot, but I would also recommend:
1. Verifying fuel pressure.
2. Inspecting/cleaning PCV valve.
3. Inspecting wiring harness for cracks, shorts, cleaning grounds, etc
I can loan RichD my wideband to check the AFR on your car. I agree with checking the wiring harness.
I also have a Janbo Djet tester I can loan RichD to test your system.
I just installed a wideband sensor on my car but haven’t looked at the readings yet since keeping it running at all has been a challenge and knowing that the air fuel mixture was likely way off because trying to keep it running requires openening air bleed screw on the throttle body quite a bit.
I will check the readings though.
Post a pic of your engine compartment.
Are you running a decel valve?
So your d jet setup is for a 74 2.0?
I'm using the decal valve.
75 2.0 with smog removed.
Using '75 ECU, MPS and appropriate CHT sensor.
I just rebuilt the distributor and installed new trigger points- didn't change anything.
Fuel pump is new, but that doesn't mean it's working correctly or the pressure is set correctly. That said, if it runs at ~1600 rpm when cold for a few minutes, it seems unlikely there's a fuel pump/pressure related issue. no?
I'll try disconnecting the T1/ambient air sensor to see if that changes anything.
Measuring fuel pressure is on the list too now.
How do I tell if the distributer is working correctly?
It still feels MPS related to me...
If you disconnect the T1 sensor I just want to see if things get incrementally better. If so, that might suggest a lean condition (also possibly suggested by the hunting idle). From there you could look to the actual root cause. But without a wideband sensor or other info it's hard to tell what the actual situation is (too lean, too rich, neither), and so to some extent you're chasing your tail.
Normal MPS failure is toward a rich situation. Why do you think it's MPS related? MPS's are pretty easy to test.
When you installed the new trigger points, did you calibrate them at all?
Its frequently the case when the MPS is going bad...that the system has been adjusted to compensate for a failing MPS. Then when the new good MPS is installed...the system itself is not in adjustment and seems wrong. Fuel pressure is changed, the air bleed screw is changed, the ECU idle mixture knob is changed and who knows what else.
For example, it was not mentioned above that the fuel pressure was checked. Its basic and important so use a gauge and check it. Then balance idle sped with the air bleed screw when warm.
Is the cold start valve leaking? Test it or take it out of the system.
Are there any vacuum leaks...gaskets, fuel injector tip seals, the air plenum etc.?
All these can affect idle and mixture.
food for thought
Ok, more testing = more results.
Distributor canister won’t hold a vacuum. Only the retard side is hooked up, and that will effect idle, (if I understand how it works correctly), but if I disconnect the retard hose and plug it at Bothell the TB and the dizzy, issue is still there.
So after finding that issue...
With all hoses disconnected and capped my AFR tells me that ratio goes from 14 to full lean in synch with the fluctuating idle.
I don’t have a tool to measure fuel pressure (yet) but I did stick my ear down by the fuel pump and it gets louder/quieter as the idle surges up and down. Hmmm... May have just identified the main culprit.
Hopefully it’s just a clogged fuel filter, or it could be a bad pump (even though it’s a new Bosch unit(which would $uck). I cleaned the tank and installed new sock a few years ago so that should be ok.
Can I run the pump without fuel for any length of time without damaging it to test it?
Where can I get a good distributor canister? Are they rebuildable?
Good news is it sounds like you confirmed the condition (lean), and you are getting closer to the root cause (failing fuel pump or possible obstruction in the line somewhere). Fuel pressure gauge would confirm it's on that path. BTW, don't cap the ports at the canister. Those need to be able to move.
The stock pumps are somewhat cooled by fuel running through them, so running without would burn them out (at some point). Not sure about the newer Bosch units. I figured those are pretty reliable (I have been running one about a year now), but who knows?
I'm not sure about the canister. Either WTB for canister or bite the bullet and get a 1-2-3? It's pricey, but works like a champ. I'd work to get the fuel delivery situation resolved and then reassess the distributor.
Found this series of D-Jet Articles online.
You are running lean at idle. Try truning the ECU knob to the full clockwise position.
I don't know if it's the ethenol in the fuel or what, but my 914 idle hunts the least with mixture knob set to full right (clockwise).
I don't think this will fix your problem, but may improve it.
A lean condition may also be corrected by increasing the fuel pressure a psi or two, by eliminating vacuum leaks, unplugging TS2 sensor.
The idle hunt isn’t a slight hunt. It’s from 1000 rpm to almost 0. The ecu and throttle body screw are adjusted to allow it to run that good.
Thinking about this more as I wait for a new fuel filter to be delivered, I’m starting to question fuel being an issue since when the engine is cold it idles high for a good couple of minutes. Then I remember that the fuel pump gets quieter when the idle drops.
I’m still going to replace the filter and check the pump while I’m at it and then we’ll see where I am at. If it’s not one of those, then I think it’s the MPS.
Okay, problem remains after replacing the fuel filter and verifying the fuel pump is doing its job.
Some new info though that I can’t believe I didn’t notice before:
I verified the timing (again). It was slightly off. Vacuum line was disconnected and plugged. After setting timing and with the vacuum line still plugged, it idled steady at ~1800 rpm. No fluctuations in idle. As soon as I plug the vacuum line back into the distributor vacuum canister, the idle drops to 1000 and fluctuated between 1000 and almost dying. Remove and plug the vac line and it’s back up to a steady 1800 or so.
No amount of adjusting the throttle body screw will bring it down to 1000 with the vac line connected. I can get the idle higher, but not lower. The ecu knob is effective at only keeping the rpm stable at idle (as it should).
AFR reading reads a steady 13.4 when I the vac line is disconnected and plugged.
Does this mean it’s my distributor that’s the prob? I know the canister leaks, but shouldn’t it still idle around 1000 even with the dist vacuum line off and plugged? Does that point to an mps that is bad or needs adjusting?
No effect during adjusting the air screw points to a vacuum leak.
If the air screw is fully closed, the engine should shut down because it would have no air for the combustion process. When air is still getting into the intake from somewhere, it keeps the engine running when the air bleed screw is closed. This is 'free air' or uncontrolled air - air that should not be getting into the intake. A vacuum leak.
I think you may also want to verify your vacuum lines are hooked up correctly.
AAR is good.
Eschewing vacuum leaks for a second…
Questions about the distributor operation under current conditions. Bare with me…
My distributor vacuum canister is bad- but will hold vacuum for a second.
So the advance plates move with retard line connected (retards timing/slows idle) but because the canister leaks, the advance plates return to their resting position quickly even though vacuum is still applied.
This would explain why the RPMs drop to the correct RPM when the line is hooked up (retard is applied) and why the idle doesn’t hold steady (canister can’t hold vacuum; timing doesn’t stay retarded), but not why the idle drops to almost 0 RPM, vs going up when the timing is no longer being retarded.
Shouldn’t the idle go up well past 1000 RPM when the canister stops holding vacuum? (retard not applied anymore, timing is advanced), especially if there was a vacuum leak? If there was a vacuum leak, why would it even drop to the correct idle speed when I first hook up the vacuum line? Wouldn’t it always remain higher than ‘normal’? My AFR reads full lean when the idle drops to almost 0, and the idle drops when the distributor canister can’t hold (retard) vacuum. The engine almost dies, and then retard vacuum is available again (canister diaphragm is 'reset' and holds vacuum for a second) , RPMs go up, and then the dance repeats itself.
Could the distributor be directly or indirectly responsible for the drop in idle when it can’t hold vacuum for retard? Is there a way I can rule the distributor out of the equation besides installing a new one?
Sounds like the source of your vacuum leak is the bad distributor advance/retard can. Put another one on the dizzy that will hold a vacuum on both the advance and retard ports, and your problem should be solved. Djets are extremely sensitive to fantom vacuum leaks.
Playing with it again, now it only idles high when cold. After idling high (AAR is working), it warmed up, dropped idle to 1200 rpm and held there for a minute or so. Then it did it’s usual go from 1000 rpm then drop to almost 0 unless I opened the throttle body bleed screw quit a bit. This time it didn’t matter if the hose to the vacuum canister on the distributor was connected or not.
Now it runs for a few seconds with the idle fluctuation and dies after a few cyclyes.
If there was a vacuum leak it would idle high, right?
Could this all be sign of a bad distributor? (BTW, I verified the MPS holds vacuum).
In my experience a vacuum leak causes the idle to hunt as the mps tries to adjust for it, resulting in your symptoms.
I'd say not dizzy. The thing about the dizzy that affects idle timing is the vacuum ports / advance plates. You've been through that. Or have you? The gunk between the advance plates can cause intermittent sticking. Might need to take it all apart, clean, relube, and try try again. (I've been through that and can share pics and tips if you go there.)
Seriously at this point, just get a 123 dizzy. Even if it doesn't solve your problem, it's an upgrade you'll be happy with. You won't regret that expense even if it only rules out problems.
Any chance this is a compression issue?
Updates and new info:
Installed new coil and 123 ignition distributor. Install was cake thanks to posts by others here.
Homemade smoke machine revealed 2 vacuum leaks which have been taken care of.
Current situation: I am able to get the car to idle at a steady 1200/1300 rpms. AFR is ~13.
The only way I can get the idle lower is if I move the TPS counter clockwise, but as soon as I do that, the idle drops to almost 0 and maybe comes back up a bit once or twice and then the engine dies as the rpms drop again. Calibrating the TPS puts the idle at 1200/1300.
The ECU knob will change the enrichment when the tps is adjusted to iallow a steady idle at 1200rpm.
When it’s at 1200 rpm the throttle body idle screw won’t bring the rpms down any further.
No vacuum leaks under the butterfly. If I take the air cleaner off and cap all lines, I can easily get the car to die by closing the bleed screw, indicating no vacuum leaks.
So could my TPS be bad? Is there a condition by which it could not allow a correct idle? Was thinking maybe I tweaked one of the contact arms when I cleaned the board. Looks ok though and the board is in good shape.
Or am I in MPS adjustment territory now?
Just to be clear, I believe there's only one setting (not adjustment) for TPS - it's either calibrated correctly or it is not. It is easiest to do it by removing it, but I have done it while still mounted on TB/plenum. I don't think that's your issue.
What curve are you using for the 1-2-3, and are you using advance or retard on the port?
FWIW, once I installed the 1-2-3 I noticed that the idle speed was very sensitive to fuel mixture compared to the other dizzy that came with this engine (which was not correct, it turns out). With the 1-2-3 it does idle rock steady, but no matter what I do I really can't get idle below 1000 even with bypass screw all the way in. I try to run idle A/F around 13.5 to 14.5 to keep it steady around 1000. If I go richer than that I get idle closer to 1100/1200, IIRC. Much leaner and it will start to hunt. I also chased vacuum leaks for a long time, to the point of swapping out plenums and trying to spray carb cleaner everywhere, but I never found anything.
I can't recall, is this stock 2.0 or 2056? If stock, and the MPS holds a pretty steady vacuum and is correct for your ECU, then that shouldn't be the issue.
Stock 2.0 liter with correct/matching FI parts. MPS holds vacuum.
113 dizzy is set to ‘B’ to retard the timing at idle (like my stock setup).
If vacuum leaks are gone, seems like that only leaves adjusting the MPS? Before my old MPS went bad, the car idled at 900 rpms.
Beyond frustrated now.
Started again from the beginning- timing.
My fan only has a single mark- a red one, notched at 7.5 degrees from TDC. I can’t find any other evidence of another fan like mine.
I guess maybe I’ve been tuning it from the wrong mark for the last 10 years (?!) as back then I used pelican’s template to find the 27 advance mark off of the 7.5 mark.
Verified where TDC and 27 BTDC actually was. Car now starts and idles high when cold (too high) and then when it warms up it dies and won’t start again.
WTF? Before I could get it to idle, albeit high, now it won’t run after it warms up.
Setting the timing to where it was doesn’t change anything. I feel like it’s flooding when trying to restart. Engine seems hot- distributor gets too hot to touch after several attempts to restart it. Fuch this thing. Getting ready to push the car off a cliff.
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