Had a customer bring in a 1989 Chevy Van G20, 5.7L with a stumble issue and intermittent stall. The check engine light was on .The check engine light codes can be Extracted without a scan tool. The code that was extracted was Code 42 : Electronic spark timing (EST) circuit fault.
A quick read of a great article on Code 42 that covers the specific components involved : The EST system consists of the ignition module, computer (ECM/PCM), and the connecting wiring.
Used a Multi-meter to test and check the wiring and found no issues, but what was noticed is the fuel injectors would click several times by themselves with the key off. This was a bit strange, but lead me to believe there had to be a short somewhere causing this and sure enough there was an internal short in the ECM. Purchased an ECM for the local parts house for just under $100.00 and replaced it. The engine no longer has the stumble and it no longer puffs smoke when you start it up (originally thought to be valve seals gone bad).
Customer happy!
Side note* I did try a new EST first as it was easy to get to and a quick test. It is located under the drivers seat along with the ECM.
