1990 C4, first a little history. Had a no spark condition, eventually found the pickup coil was bad. Had no resistance. I had purchased a new module, thinking that was the problem, but have no way to test it. Pickup coil was an easy find. Replaced both parts, got it back togethor, and it did not run right. Engine would not advance, or accelerate. Even had the headers/pipes get hot and turn red!! Kinda scared me, so I figure I had the timing off. I struggled quite a bit trying to get the base timing back down to 6 deg. I had it too far advanced or retarded. Kinda embarrassed to talk about it. Regardless, spent 2 hrs on it this afternoon, and I have it running on bypass, and was able to nail it down to 6deg timing. Engine kind of idled fairly decent. But when trying to rev it up, kinda stumbled, and back fired, did not accelerate again. Now for the punchline. Hooked the bypass connector back, up, and reset the computer. Engine now wont run!!! Try's to run, pukes, I give it a little throttle, but eventually dies.

Could the engine computer be bad now? WTF, I dont need this! Car has been off the road for over a month now, I need to drive it! Anyone have an engine controller do this? It is NOT the original ECM, and I certainly dont have a spare. I do program my own PROMs, and yes i swapped that out with the same results.

I am thinking, that I put this all togethor correctly, the first time, but now I have a new problem! Any ideas?
Mike

 

Yikes. Getting pipes red hot equals retard timing. Did you pull the EST connector. Aka Adv timing. This step is a must setting the base timing.
You mention your ECU / prom. What happened to the OE. ECU. We will assume you have the OE prom.
Ps. What is the fuel pressure.

 

Ya, I'm sure I had the timing off, when i first got it back running. And yes, I pulled the set timing connector to set the base. Original ECM was changed by previous owner. And yes, I do have the original PROM, but did not try it. Just went back 1 chip rev, to see if that version had the same problem, and it did. Fuel pressure was checked, when I first had the no-start condition, and it was fine. After that, found that I had no spark.
The only good thing I can say, is that this whole problem, started with my car sitting in my garage!! So, no tow-job was needed to get it home!
Last night, spent some time with my FSM, reading about the timing. May have found something to look at. I should be able to check it out today. Stay tuned!

 

Well, no luck. After reading my FSM, got to looking at the ground wire, that comes into the dist via a 4-wire connector. This ground is needed, as a reference for the ECM, to make adjustments to the signals going thru the ignition system. The wire goes thru a little terminal block, and attaches to the base of the dist, via a metal screw/tab. It was all good, but still cleaned things up a bit.
Engine still won't run with the ECM connected. Pulled the timing connector, and it will idle fairly decent, hunting around a little, but I think it was like that before. Checked base timing, and it was right on 6deg BTC. I need to phone a friend on this one!
I'm really not looking forward to replacing the ECM!