In this 89 tpi 350 gta we are fighting an intermittent no-spark issue.

Right now there is none. We have power coming out of the coil to the cap but nothing at the plug. It appears to be a new coil.

Coil, distributor, icm, are the main components, the ecm controls the icm.. the icm is in the distributor, yes?

Thinking about swapping out the icm or possibly the whole distributor. It's definitely old. I hate throwing parts at an issue, but we are trying to get this bitch fresh and time is valuable.

We where told when we got it that it would run, get hot, and shut off. After a new starter and a tune up it was running well yesterday. We never saw the no start issue. Today, no Spark. Every now and again it may fire off a cylinder or two while cranking, then back to nothing.

Advice appreciated.
Thanks y'all,
6

 

you should swap the distributor with another one and see how it runs.IMO, the small cap HEIs are crap-I have two of the things in vehicle fleet...for some reason,GM made these with excess gap between the rotor tip and the cap contacts-causing lots of ozone buildup that attracts moisture and causes rust on the reluctor and sometimes the reluctor magnet will disintergrate-sending weak signal to the ICM...The ECM does not trigger the ICM ,It only controls spark advance. If you have strong spark at the coil,the fault lies with a faulty rotor,cap,or wires.

 

I can second what 8t2 said. Mine has done exactly that in the past. Fine one day and then nothing, rolls over with the occasional fire, spark to the distributor but not at the plug. Chase your tail forever and ultimately it's the ICM or the pickup coil. At that point it's easier to put a new distributor in and eliminate the individual components. Oh and keep a spare new ICM around, it won't be the last time ...

 

Spark will always find the easiest path. Now this might not be exactly related to your problem but on my 95 GMC Sierra truck (305 TBI), over the years I have found the factory stock coil wire corroded at the cap coil connection, and most recently with a completely new replacement dist, cap, & rotor the spark arcs through the rotor to the center post on the distributor and grounds the spark out. Almost impossible to see. You have spark at the coil wire, so spark goes into the cap, but never comes out. Now I carry a spare rotor.
Do you use dielectric grease?