Engine trouble, Dies at idle Options

[trojanhorsepower]

All,
I have been enjoying my car but have a recurring issue.
Starts great
Runs fine for maybe 20 min
Starts to once in a while act like it turned off for just a 1/2 sec then comes back on - causing the car to lurch and the shifter to jump
After about 30 or 40 min the car dies if stopped and allowed to idle. It just drops off spools down to nothing,
It restarts if you hold the gas peddle all the way down. Sometime when it restarts it is weak, then it goes fine.
As long as the car is in gear and moving it does not die.
It will continue to do this until I get home. If I am coordinated enough I can shift into neutral, work the brake with my left foot and keep the RPMs up a bit with my left and it seems fine (no stumbling or trying to die at higher RPMs) but if I come to a light, stop and let it idle it will just idle down to nothing.
Sometimes when I get home it will idle fine until I turn it off. Other times it just dies.


Seems to pull great all through the range
Always restarts

Any ideas where to start?

Thanks

Peter

[emerygt350]

Now that I have a moment to type...
Was this orgianlly a 2.0 or a 1.7? Can you send a picture of your sparkplug location? What is the block number on your engine? It should be up behind the oil/pcv bowl on the front of the engine.


Some next steps:
1) Check to see if your MPS holds vacuum. If that isn't the case, you need to address that before anything else.
2) after 1, get those resistance readings from the CHT sensor. Either in car or pull it and check on the bench (best) and that way you will know what kind you have in there.

History: The 1973 MPS and ECU were basically cobbled from the 1.7 for the first year of the 2.0. They basically took the 1.7 MPS and put a spacer in it and tuned it for the 2.0. If the epoxy plug and the rivets are still in it, likely that has not been messed with. However, that means you have an old diaphragm in there and chances are that might be part of your problem. A crack will lead to a rich condition. The worse the crack the worse the condition. A leak down will tell you right away if that is the problem. It should hold 17mmhg for at least 5 minutes. If all is in perfect order (seals, no cracks), forever.

As far as I can figure from the sources I have read the 037 ECU was simply a rebadged 1.7 ECU for 1973. I am not super confident in that because I believe there were some changes due to the TPS but for the most part as far as AFR circuits, I believe the strategy was just tune the MPS and cheat the CHT to make up for the displacement changes.

The other 1973 mod was the inclusion of a ballast resistor inline with the CHT sensor. This richens the 73 to compensate for the displacement (along with the MPS tuning). I am a little surprised they couldn't compensate entirely with the MPS but the resistor is simple and easy. Check to see if there is a resistor inline with your CHT. That could be creating problems with the 1974 044 ECU.

Now, if your car has the resistor, a 73 CHT, and a functioning 73 MPS, you are actually in likely the cheapest troubleshooting position. ECU's can be had for cheap (e.g. I have a known good extra 037 I picked up just in case). To replace your MPS with an 044 to mactch your ECU is likely the most expensive option, but I have not priced out options on 044s. They might be easier to come by.


Now, this is just to get to a point where you can confidently troubleshoot. It is quite likely the mismatch or a faulty MPS is your problem, but it may not be.

Some things I would install for the future:
1) A CHT sensor on #3 plug. Dakota Digital sells a good one.
2) An Air Fuel Ratio gauge and wide band O2 sensor.
3) The Tangerine racing MPS tuning kit. The diaphragms are currently gone but Chris is working on getting a replacement for those. All you need to have is the awesome screw driver tool and the full throttle stop screw. If your diaphragm is good, you wouldn't open the MPS, just remove the epoxy, the full throttle stock stop screw, and replace with the new one for tuning. Ask for help before you do that (if you do) since it is easy but you will need to ensure the depth of the stop screw is correct.

You need those things to make a 2056 run correctly without melting down due to lean conditions.