Tom454

The Factory Service Manual p.8A-20-8 shows two modules:
1) "Electronic Spark Control Module ESC (in fender)
2) "HEI Module" in distributor

also- "Electronic Spark Timing (EST) Distributor" which refers to the distributor plus the HEI Module.

However, when you try to order these parts, the aftermarket switches and confuses the names. You have to go by their pictures. I ordered the "ICM" from one vendor which is in fact the ESC.

Anyways.... I suspect the entity inside the distributor... the HEI Module or as we all affectionately call it the ICM.

I should have ordered the ICM instead of the ICM. Pun intended.

Tom454

Oops... it's a 87.

Tom454

Yes.... but my Digital Dash need new horse shoes. It spazzes.

Matatk

The ESC in the fender well area is what monitors the knock sensors in the block and transmits that to the ECM to retard timing when there is detonation.

Tom454

Yes.... also... there is about a 15 distributor degree range where the engine will run... outside that, it stalls. It has a sweet spot that I am now a master at finding. LOL I left the hold down loose and set it by ear as well.

I think it's the HEI Module.

Matatk

If you read the link, it will give you instructions along with pictures. You will read the CEL in the center dash light cluster, not the digi-dash

Tom454

Yes... and according to the schematic, it only interfaces with the ECM, has no direct physical connection to the distributor. 4 wires:
1) Ground
2) +12 Volts
3) Knock sensor
4) ECM

Tom454

DOA I believe.

I even tried mouth to dash.

Matatk

Are you saying you have no cel that comes on when you turn the key on in the ignition (self test)?

Matatk

Aside from that...Don't become fixated on one piece that may or may not be the issue.

I'd still like to know the following:

1) Specific fuel pressure values key on and running
2) Coolant temperature sensor resistance value and air temp
3) If TDC was mechanically verified and if distributor was set correctly based on that. One tooth off can cause running problems.

Tom454

Just went out and tried it all again...

No codes

Turned off ignition, installed OBD1 reader with switch set to ECM A-B position ... no codes.

Matatk

You don't have a code 12? That means the circuit is functioning. If there is no light, the bulb is burnt out, circuit is bad, or you have a bad ecm.

Tom454

Distributor is out right now so I can't do a running test. When it was running, it was steady 43. Just went out and did a key on test, shot right up to 43, held for a bit, then slowly decreased. With the leaky OEM injectors key on went to 43 but then dropped almost instantly to 0.

TDC was verified at the gears and at the distributor with a valve cover off.

It runs great 1100-1900. If the mechanics were off, this would not happen.

I just pulled this from my notes (spreadsheet): "ECU fan switch 2500 +/- ohms @ 74 deg F measured"

The measured data point falls squarely between expected:
3400 ohms at 70F, and 1800 ohms at 100F

Tom454

No codes.

"the bulb is burnt out, circuit is bad, or you have a bad ecm"

Once I get it running and inspected, I can fart around with that.

This car has been grossly abused. TLC will come after the bandages are off. LOL

It's very contrary to my normal approach, but I'm gonna just throw parts at it until it runs.

I even have a 1966 points distributor in the wings if I have to.


I'll dig up a new HEI module first.

Matatk

The values you posted look good.

Back to the codes - that's the first thing I'd be inspecting. Car doesn't need to run to test the circuit/values. There is a troubleshooting chart in the FSM.

If it were my car, I wouldn't do anything else until I verify the ECM is good.

Tom454

Bad ECM is a definite possibility.... the one that's in it is a reman.
This will be my last port in the storm.... it's a big ticket item. I have no way to test the one I have.

Just checked my orders... I have a new coil, a new ICM, and a new ICM ordered.

Ha Ha... the HEI Module and the ESC Module are BOTH listed as the "ICM" by the parts vendor.

Tom454

You are correct. It will not run without the OEM HEI module providing feedback to the ECM.

I rebuilt one of my old Accel HEI distributors with a new 2 wire HEI module, new cap, new rotor, and new coil. A duplicate of this distributor is in my carbureted 86 Silverado where the 4 wire connector to the ECM is just dangling in the engine compartment. I have been driving this truck like this since 2000. So, I thought maybe I could get away with it here.

No go. The renegade distributor functions perfectly and provides the correct spark. But.... the injectors won't fire. I tested this by removing the MAF tube and spraying starting fluid into the throttle body. The engine fired right up.

So to answer my original question.... no. You can't just drop in a "1 wire" HEI distributor to bypass the OEM electronics. You won't get any fuel from the injectors. Case closed.

New HEI module & ESC will arrive in a few days and I can start from scratch. If they don't fix it. I'll order a ECM. If that doesn't fix it, a new carburetor.

Bfenty

Had a similar issue, was the Ignition Control Module. It's a cheap part and easy to replace, they go bad from heat often, and a big sign that they're going out is the problems get worse when the engine is hot. (IE-won't start until the engine is cooled off)

Do you have a Factory Service Manual? If not I'd highly recommend one, lots of good diagnostic info in there. It'll keep you from throwing parts at it.

hemivett

I had a bad o2 sensor, that did the exact same thing. Wouldn't idle, and wouldn't get out of its own way. Just a thought. h

Tom454

Replaced that as well since the original post. Didn't help unfortunately.