Engine trouble, Dies at idle Options

[emerygt350]

Ahh... That is what I feared. You have a 73 mps and a 74 computer. This may not be terrible but it will make troubleshooting difficult. The next issue is going to be figuring out which cht sensor you have.

[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.

[BillC]

Hopefully this is just a silly question, but what cam is in your engine? Since it's a 2056, it's been rebuilt (obviously), so they could have changed the cam.

Your symptoms sound a lot like what I was chasing on my car when I was first trying to get it running again -- it would run fairly well at higher RPMS, but it would just wind down and die at idle. In my case, the rebuilder put a too-aggressive cam in the engine that isn't really compatible with D-Jet.

Do you have a vacuum gauge? Have you checked your vacuum levels at idle? If so, what do you see when it's running and also when it run downs and dies? If you see fairly low vacuum at idle, like 8-12", and that vacuum goes toward 0 before the engine dies, it might be your cam.

I was finally able to get my engine to idle fairly reliably on D-Jet, but I had to set the idle to 1600 RPM to make that happen.

[emerygt350]

If you are running the timing retard currently, removing that would help if it is a cam issue.

[trojanhorsepower]

OK, Thanks all,
No idea what the cam is. IT came with the car years ago, but the previous owner had done some research to build a 2056. I think if it was the cam it would be bad all the time, not just when hot, no?
The timing is set a 27 deg advance at 3500 rpm, but I have had this issue over several different timing settings, but maybe worse now? Timing was set a 27 deg at 2700 rpm last I think, but this time I couldn't remember and looked it up in one of my books and that is what was spec. I have not tested the vacuum.
There is no resistor in the engine bay on the CHT wire. Could it be somehwhere else?

Thanks

[trojanhorsepower]

Forgot: The MPS was tested when we put the engine in, but could be bad now though. The computer was purchased separately, but I have the original. No reason to think it's bad. I could swap it out.
It was an original 2L. Ill continue to test post here.

Thanks

[emerygt350]

Do you have a mighty vac? Easy to test the mps to see if the diaphragm is cracked. What is the number on the original ECU? And the only spot for the resistor is in line at the junction by #3.

Is you dizzy a dual port (retard and advance?) and are the hoses hooked up and to where?

[trojanhorsepower]

Yes, I will test the MPS.
Dizzy is a correct 2l I think it has to ports on the vacuum can.
The port off the lower back is to the green hose off the plenum, the other is a black hose off the throttle body.

[trojanhorsepower]

No numbers left on the other computer

[emerygt350]

Hmm. No way to know what that ECU is from without taking it apart probably.

The vacuum port on the can that points away from the dizzy should be connected to ported vacuum on the throttle body. This is the port that points kinda towards the distributor. The port on the dizzy vacuum can that points toward the dizzy itself needs to go to the throttle body port facing towards the rear of the vehicle. Neither line should be connected directly to plenum vacuum.

Some later 74s would have the advance port line simply laying on the engine, not connected to the port and the advance port on the tb is gone on those motors. Only the retard was used (the rearward pointing port).

Does your throttle body have one or two ports?