Here's a problem that I was faced with and (hopefully) solved a couple weeks ago:
My 1993 Chevy Lumina sedan (Eurosport, 3.1L MFI) started to play this "fun" game where it would start in the morning when it was cool, get me wherever I needed to go, but then would not re-start when it was at all warm (like not within 4-6 hours of being shut down). It would crank and turn over, but not catch. I had fuel pressure at the rail, so I was pretty sure it was a spark/ignition problem. Once cool, she would start right up.
I started testing things with my multi-meter and a test light. The spark plug wires were all original (the car at this point had 145k miles on it) and one of them tested out-of-range for resistance, especially when it was hot. It had been about 60k miles since I had the spark plugs replaced, so I figured I would learn how to replace my spark plugs and I'd change out the wires at the same time. Mechanics that I know talk about changing out plugs like it's the easiest thing in the world, but for me the job was rather difficult (but in a challenging kind of way - I'm not angry that I did it). After about 4-5 hours over two days in my garage, I managed to get all 6 plugs and wires replaced. It took rotating the engine forward and all kinds of crazy socket-extension combinations, but I felt good at the end. But it didn't solve my problem. Crap!
My wife has an uncle who is a very good mechanic, and he was nearly 100% sure that it was the Ignition Control Module, which is basically an integrated circuit board that the ignition coils plug into. The module "communicates" with the car's PCM (master computer), which gathers information from all the various sensors and tells the Ignition Module exactly how to time the firing of the spark plugs. The only problem is that this module, while very accessible on some vehicles, is buried "below" the exhaust manifold and bolted tightly to the block. Rotating the engine (like I did for the spark plugs) will move its relative location, but only to a less accessible place. It took me 2 hours to remove the ICM, 10 minutes to test it and verify that it was indeed junk, 10 more minutes to install new ignition coils (the old ones were also originals) onto the new ICM, and then another 3 hours to put the whole assembly back on (that's about 1 hour per bolt - they were that hard to reach and get started cleanly). And THEN when I was re-installing the electrical connections, I nearly (I think because of mental fatigue) bent one of the pins on the brand new ICM that I had just worked so ridiculously hard to install! Fortunately, I got everything connected correctly and it's been almost 2 weeks with no start-up problems at all.
I just thought I'd share my story, just in case anyone needed tips on how to work on your ignition system very slowly. Would I do it again? Maybe in a few months I'll have forgotten enough to say yes.
Saturday, January 12th, 2008 AT 8:40 PM