Time to get some other peoples input on this one...

88 GTA former TPI car converted to SD with the EBL P4.

Driving down the road at cruise speed, the car will suddenly stall out, intermittently. It will come back to life several times, and sometimes resume normal operation before it coasts to a stop.

While the problem is occurring, key on, engine off, the SES light will flash off momentarily. Sometimes it seems like its in a rhythm as if it was a circuit breaker tripping and resetting every couple of seconds. Voltage read through my laptop will be low and unstable. Fuel pump voltage also reads low. I can't recall if I get fuel pump prime while its occurring.

Things I know:
G118 (at the back of the pass. side head) is GOOD. the ECM tosses a couple of codes, so I assumed ground issue at first. If there's another ECM ground, I haven't found it in the schematics.

Battery voltage is good. It will crank forever, just won't fire. I haven't been able to reproduce the problem by wiggling any of the accessible wiring harnesses.

I'm working on getting the problem to happen again while I have my multimeter handy. Last time I had it happening, I discovered a bad alternator and concluded it was the combination of loose battery connections and a bad alternator, but turns out that's not it. Any ideas are good ones, I'm stumped on this one.

Thanks for reading.

 

While data logging, sensor readings are erratic, but on my DVOM, the sensor voltages seem to stay rock steady. That does not seem so be a good sign for the ECM... I'm also seeing injector pulse width being commanded while its key on, engine off. Otherwise the ECM seems to be acting normally, CTS temps getting false readings high enough will trigger fans and such...

 

In the harness, you will see a point near the HVAC box where the harness splits to run to the front of the car behind the pass side headlight. Within 3 inches or so of that point is a splice for the constant power circuit for the ECM and fuel pump. I had mine fall apart on me for absolutely no reason other than age. If that junction is starting to come apart, there will be a power loss to the ECM and fuel pump intermittently.

You would be looking for a mass of ORANGE wires.

 

I will have to check that splice. I know exactly the one you are talking about. There's also a ground wire splice in there that may be faulty

 

Don't forget that the splice is covered in what is essentially duct tape and it's really sticky and gooey. Which could be all that's holding the wiring together.