MPS, Rebuilding the MPS Options

[Ron914]

I made the tool needed to remove my CHT and I noticed it had some tape on the connecting wire ,once removed I saw that the air e had been cut a bit so I installed there new sensor expecting the problem might be solved but it was not ,in fact I think the car is back to running rough again with the new sensor . Missed out on a great buy last night for a D-Jet testing box that goes between the car and the ECU that probably would have diagnosed my problem. I guess I am going to need a new wiring harness and posibly another ECU but this is getting expensive .
I checked my IR thermometer against the water boiling pot I have and when the water is boiling (212 F) the gauge only is reading 196F
Tested the old sensor
Cold@81.5 F = 1.149kohms
Hot @ 212 F 220 ohms but starts rising fast as it cools ,went to 244 F in ~ 1 minute .
Currently the new sensor is in the car . I was hoping the new sensor was going to be the fix . Not sure which direction to go at this point .

[Ron914]

I decided to verify the condition of the CHT wire #23 @ the ECU plug and it looks fine .

I think I am going to look into purchasing a new meter as I have had the one I am using for many years now , maybe the leads are bad but my readings are not what I expected .
Maybe I might need a new ECU . I tried the sniff test but it just smells like old 50 year electronics to me can't really say if it has a burned smell or not .

[Superhawk996]

Flukes rarely go bad

New leads are much cheaper than a meter.

Keep digging - there has to be a reason old CHT is checking OK on bench but was measuring 50 ohms when in car and hot.

So issue could be either in car, in your leads / meter, or how & where you’re measuring chassis ground from.

I was just doing some work the other day and a test lead went bad. Annoying . . . you always have to be aware of and checking your test equipment when things stop making sense.

Keep powering on!

Is the car still stalling when it gets hot? What is the new CHT measuring when it stalls?

[ctc911ctc]

Flukes rarely go bad

^^^^^^^^^^^^^^^^

(IMG:style_emoticons/default/agree.gif) (IMG:style_emoticons/default/agree.gif) (IMG:style_emoticons/default/agree.gif)

TRUE RMS - Great meter!



New leads are much cheaper than a meter.

Keep digging - there has to be a reason old CHT is checking OK on bench but was measuring 50 ohms when in car and hot.

So issue could be either in car, in your leads / meter, or how & where you’re measuring chassis ground from.

I was just doing some work the other day and a test lead went bad. Annoying . . . you always have to be aware of and checking your test equipment when things stop making sense.

Keep powering on!

Is the car still stalling when it gets hot? What is the new CHT measuring when it stalls?

[Ron914]

Yes the car is still stalling after 5-10 minutes of running .
Car starts right up , goes to 1400 rpm as it should with AAR open .
I am definitely bothered by the temperature readings , something not quite correct . I boiled water in one of those instant heat tea pots and when boiling the IR just is off by ~ 16+ degrees .
I take the head temp readings at the intake bolts on the head that are exposed and the oil temperature at the oil sender(taco plate ) fins bottom of motor.
Here's a photo of my oil temp gauge vs the IR thermometer( which might be close to -16 degrees off) . My oil temp sender has 200C stamped on it .

[emerygt350]

Your not at a higher altitude are you?

16 isnt enough to really hurt things. I think you should try the pot at this point. If you can keep it running by just turning the pot down you know it's something in that circuit pre ECU. If you can't then you know the problem lies elsewhere.

I do have a known good ECU you can borrow any time. You would just have to add the 270. It should still run your car. I think.

[Ron914]

Your not at a higher altitude are you?

16 isnt enough to really hurt things. I think you should try the pot at this point. If you can keep it running by just turning the pot down you know it's something in that circuit pre ECU. If you can't then you know the problem lies elsewhere.

I do have a known good ECU you can borrow any time. You would just have to add the 270. It should still run your car. I think.

Thanks for the offer. Yes ,I am at sea level .
I have just made a deal to purchase NineFour Tronics D-Jet tester , this should help me get to the bottom of things . although a bit pricey I am sure it's worth every penny and maybe I can use it to help others that are having issues with their D-Jet systems . I have that resistor still I purchased from AA .

[emerygt350]

At the least you can resell it. Just remember, those things don't really tell you what's wrong. They just tell you what is outside of parameters. I am very familiar with that from my obd1 mustang. You can end up replacing every sensor in the engine just to find out you had a bad ground.

[cgnj]

I'm curious where these diaphragms are being sourced from. Tangerine Racing as them as out of stock. I have two in my djet parts container. I hsve never used them because I am a notorious carb fan boy.

I have the parts to build a 2056 and was thinking or refurbing all of my djet stuff. I decided to do a stealth after reading Gregs Amy's Microsquirt conversion blog. It just doesn't make economic sense to me to pour all the time, money, & effort into an analog, fifty year old FI system with a boat load of NLA parts and no engine build flexibility.

I get it that money is in originality. This is something that I'm struggling to wrap my head around.

I just bought a MY 73 1.7 with ICT 34s. Going to use it as my test mule for my djet stash so can be confident that everything still works after sitting in boxes for 25 years.

[emerygt350]

Go for it! I love a carb too but this is like a crossword puzzle that you get to drive. I love the troubleshooting. Ala the failed distributor I just dealt with. These early fuel injection systems are so interesting because they had to approach the problem of air fuel ratio without an O2 sensor. I find it fascinating. And when you get it to work, it works better than a carb, which is a nice return on learning.

[Superhawk996]

Yes the car is still stalling after 5-10 minutes of running .
Car starts right up , goes to 1400 rpm as it should with AAR open .
I am definitely bothered by the temperature readings , something not quite correct . I boiled water in one of those instant heat tea pots and when boiling the IR just is off by ~ 16+ degrees .
I take the head temp readings at the intake bolts on the head that are exposed and the oil temperature at the oil sender(taco plate ) fins bottom of motor.
Here's a photo of my oil temp gauge vs the IR thermometer( which might be close to -16 degrees off) . My oil temp sender has 200C stamped on it .

IR temp sensors are sensitive to what the emissivity is set at.

Silver surfaces are usually a little low. So not surprised by the 16 degree variance. Emissivity of Aluminum is all over the map. Better if you could get a reading off the black steel taco plate where the oil temp sensor lives.

Remind me. . . Did you ever check under your tin for mouse houses? Borescope works great but can also be done wire small inspection mirror through spark plug holes

Also remind me - did you have cooling flap position verified?

What is the new CHT measuring when the engine stalls? Is that the 0.3 ohm reading?

[Ron914]

Yes the car is still stalling after 5-10 minutes of running .
Car starts right up , goes to 1400 rpm as it should with AAR open .
I am definitely bothered by the temperature readings , something not quite correct . I boiled water in one of those instant heat tea pots and when boiling the IR just is off by ~ 16+ degrees .
I take the head temp readings at the intake bolts on the head that are exposed and the oil temperature at the oil sender(taco plate ) fins bottom of motor.
Here's a photo of my oil temp gauge vs the IR thermometer( which might be close to -16 degrees off) . My oil temp sender has 200C stamped on it .

IR temp sensors are sensitive to what the emissivity is set at.

Silver surfaces are usually a little low. So not surprised by the 16 degree variance. Emissivity of Aluminum is all over the map. Better if you could get a reading off the black steel taco plate where the oil temp sensor lives.

Remind me. . . Did you ever check under your tin for mouse houses? Borescope works great but can also be done wire small inspection mirror through spark plug holes

Also remind me - did you have cooling flap position verified?

Motor was rebuilt so no mouse issues.Flap position is open but the thermostat that operates it is not working so flap is kept open all the time .

What is the new CHT measuring when the engine stalls? Is that the 0.3 ohm reading?

the 00.3 ohm is the resistance of the wire from the CHT connector to the ECU pin 23, I wanted to make sure I had a good wire going t o the sensor . The car is so all over the board , I went out to start it up for a test so I could give you those values but now the motor does not want to run again ( very rough idle and stalls )

[Superhawk996]

Ah - OK so you have a good wire from sensor to ECU.

Here’s the thing - walk away when you get too frustrated.

The no start right now is an interesting symptom that may eventually lead somewhere.

When you get a situation like that I’d start a note / log to keep track of data.

For example: record the current Temp and CHT measurement and any other known data (like how it it does or doesn’t idle, whether or not you smell fuel, whether or not you have spark) etc.

I’d probably just let it sit overnight and try again in the morning when it’s stone cold but would measure CHT before I even crank it. Then see what happens. If it does the usual and runs for a bit then stalls, record the CHT and measured temps (gauge + IR).

Keep track of what you’ve done and what happens. Make sure in the process of disconnecting ECU connector that you haven’t disturbed something else or just didn’t fully seat ECU connector. Likewise these engines use simple spade wiring connectors and it’s just way too easy to bump a connector or ground loose and then chase created problems.

Hang in there!

Slow and methodical wins every time vs shotgunning parts

[emerygt350]

I always do a visual before hand as well. Mps vacuum and connector for example. Connections on the coil. Stuff that can easily be jostled while poking around in there.

[Puebloswatcop]

Where can I obtain a MPS re-build kit with a new diaphragm?

[FlacaProductions]

Unless someone is going to sell you from their stash, they are currently not available. Chris at Tangerine said that he's hopeful to have a new run before the end of 2025.

[Ron914]

Getting back to my D-Jet issue , walking away is what I do when things get a bit frustrating , coming up with another plan .
Well I purchased this test device for D-Jet from a member here . Although I have tested with my DVM these connections /values it really made it easier to take the readings .
I noticed when I checked my fuel pressure after 5 minutes I had a loss of 2 psi , not sure if this indicates a leak somewhere but I do still have a gassy smell inside my car . I have replaced the old plastic lines with SS ones and all fuel hose has been replaced with Cohline braided hose from the bird . The fuel tank was also removed and checked but I did not do a pressure test on it , the gasket inside the fuel cap was also replaced .( this is a separate issue and doubt it is the reason for my engine cutting out at 212F) .
I also figured out why my Dakota digital was reading so low ( it was in Celsius mode ) so when I said the motor quits running at 100 that really is 212F . I had to call their customer service and have them send out a new plug as one of the sensor leads has come out of the factory plug .I have videos of motor start up and bad running but I don't think I will use YouTube to post as this makes all videos public . My coil seemed hot but I figured this was probably due to leaving my ignition on too long during voltage checks .I currently have the decel valve disconnected and bypassed , vacuum line disconnected from distributor . I can send a email or text the video to @Superhawk996 or @emerygt350 if you would like.




My test results

[rjames]

I'm confused (happens often).
On August 19th you posted:

Car was idling good and I drove it 10-15 miles before removing the MPS to rebuild it . I rebuilt my MPS because it leaked and would not hold vacuum for very long and was told I might as well replace the diaphragm with Chris's rebuild kit since I will need to properly tune my MPS because of the 2056 motor upgrade

I don't see any follow up posts stating that the MPS is not leaking anymore and that you tried tuning before moving on to suspecting the CHT.
If it was running ok before the MPS rebuilt, I'd go back to the MPS.
If it doesn't hold vacuum or is out of tune (usually the case after a rebuild) then it's still suspect as at least a partial cause for your issues.

If I've followed along correctly, when cold, the car starts, the AAR opens, and engine runs at 1400 rpm as expected. After the car warms up and the AAR closes, the idle drops to ~1000 rpms as expected, but stalls soon after and you notice a fuel smell like it's overly rich.

If the MPS is out of tune, or won't hold vacuum, that could be the cause of your overly rich mixture. And it would make sense that with the AAR open it wouldn't stall despite being overly rich because the AAR is adding enough air to compensate. When the AAR closes though, the car is too rich to keep running and stalls.

What am I missing?

An easy way to check the above would be to turn just the inner screw of the MPS clockwise ~1/2 a turn or so to lean it out and see if allows the engine to keep running after the AAR closes. This assumes that your MPS holds vacuum.

[emerygt350]

A 2 psi drop would lean the mix quite a bit.

That cannot be excluded as a problem. Maybe not 'the' problem but I wonder about it.

Is this very, very repeatable? 212ish every time? Sputters and dies the same way?

Anybody remember the minimum pressure for these injectors? I seem to remember something about not even being able to fire if the psi fall to a particular level.

[Ron914]

I'm confused (happens often).
On August 19th you posted:

Car was idling good and I drove it 10-15 miles before removing the MPS to rebuild it . I rebuilt my MPS because it leaked and would not hold vacuum for very long and was told I might as well replace the diaphragm with Chris's rebuild kit since I will need to properly tune my MPS because of the 2056 motor upgrade

I don't see any follow up posts stating that the MPS is not leaking anymore and that you tried tuning before moving on to suspecting the CHT.
If it was running ok before the MPS rebuilt, I'd go back to the MPS.
If it doesn't hold vacuum or is out of tune (usually the case after a rebuild) then it's still suspect as at least a partial cause for your issues.

If I've followed along correctly, when cold, the car starts, the AAR opens, and engine runs at 1400 rpm as expected. After the car warms up and the AAR closes, the idle drops to ~1000 rpms as expected, but stalls soon after and you notice a fuel smell like it's overly rich.

If the MPS is out of tune, or won't hold vacuum, that could be the cause of your overly rich mixture. And it would make sense that with the AAR open it wouldn't stall despite being overly rich because the AAR is adding enough air to compensate. When the AAR closes though, the car is too rich to keep running and stalls.

What am I missing?

An easy way to check the above would be to turn just the inner screw of the MPS clockwise ~1/2 a turn or so to lean it out and see if allows the engine to keep running after the AAR closes. This assumes that your MPS holds vacuum.

My MPS follow up was in page 3 of this long post maybe I should start a new one . I was able to locate a square edged ring and tried replacing to see if it helped my MPS leak down any better but it has not .It stills leaks down from 15inhg to 3 in about 30 minutes . My concern is I have messed with the inner screw settings enough I no longer trust the position it is at .Basically I am still baffled as to why the car doesn't run well after the MPS rebuild ,I suspect the MPS is no longer functioning correctly . I will try your suggestion of turning the inner screw 1/2 turn CW .