about to bite down on some bullets. things point towards PCM.
94 s-10 blazer W 240K miles 4x4 quit after short while other day.
would intermittent run, but never got far. maybe 5 to 10 min running before quit.
sometimes (usually) would eventually restart. initially suspected CPI.
but noid light suggested pulses were clean and bright when running and got weak when it quit.
Hearing rumors that PCM sends CPI pulses only if it gets good spark signals, I put the noid on the ignition wire into PCM. those pulses seemed weak when it wouldn't run, too (just like injector pulses).
So, I checked the ignition module--tested OK at autoparts store. checked twice since my trouble is intermittent. Bought pickup coil but didn't install (have to remove distro). New coil tests almsost exactly like the one in car...around 800 ohms. passes wire wiggle test...steady 800 ohms.

I think I am going to reassemble distro (old coil, old module and return to testing.
I suspect I should buck-up for a PCM (it is about one hundo).

I got the module hanging from harness under glove box so I can get probes onto wires. I may put a scope on it and watch traces as things fail to operate.

anyone got ideas before I do that and/or buy a PCM?

Thanks!
forum has saved me multiple times!

 

well...
reassembled. only change is cleaned inside of distro (wasn't dirty) and reinstalled old module with heat sink compound. when removed there was only a little clear silicone stuff. now it has white paste, thin layer.

ran without issues for a long time. maybe that was it. I even ventured downhill (was staying uphill so I could coast home!). I even ventured out of the neighborhood and made it back.

module was not loose or anything.

maybe disconnecting and reconnecting the wires did something.

I never unplugged the PCM connectors, but I did wiggle them trying to make engine quit running...

will post more if it quits again. now need to find time to stuff module back up behind glove box.