I have 3 people working on this problem. One is a Mech with 25 years exp, another is an avid ECM Programmer, and myself.
First off, DON'T TELL ME TO REPLACE THE PICKUP COIL. Please. I've done this on this car and other cars. Usually the distributor will fail all together, as it did on this one.
Its an 86 GT 2.8 5 sp. Symptom is erratic spark when not bypassed. Car runs rough, stalls, especially bad at cold start. After keeping it running for 1-3 minutes, SES light will come on, and car will run perfectly besides the light. If from a cold start the EST is bypassed, it will idle smoothly and not stall, and properly reduce idle as engine warms up.
First thought was PU Coil, replaced and no longer ran. New distributor, runs, but has symptoms. Swapped ECM, ditto, 3 ecms later exact repeatable problem. Checked Dist module at ECM connector for proper switching of EST and Bypass, all ok, so wiring seems to be fine. New factory chip BCC APN, same problem, same problem in all 3 ECMs. Tried another distributor, same problem.
Mech. thinks it still has a bum distributor, Programmer thinks it might have a bad ground somewhere. My only other thought is a faulty reference wire, but it doesn't explain why it runs so well in bypass, since it needs the reference signal to fire the injectors.
Any thoughts? Trying to ready car for sale, and its excellent otherwise.
Chris