1987 R10 305 No-start

[KCHilite]

Hi folks!

Newb here...I spent about an hour scrubbing the forums but can't seem to hone in on exactly what I'm looking for, so apologies in advance if the answer was right in my face and I missed it.

Got an 87 R10 with the 305. Up until now, I'd drive her a couple times a month, and she's always started every time. Only issues were running a little rough, and at long red lights I'd have to put it in neutral or else it would stall out after sitting still in Drive for more than 45 seconds or so. The SES light would usually come on too in these instances, but would go out after a half mile or so of driving again.

As of a few weeks ago, it won't start. Had it idling in the driveway, it cut out, and now nothing. There's no spark at all from the coil. Researching online leads me to believe likely ICM issue, but it seems it could easily be distributor related too. I was going to go pick up a new ICM and try it, but before throwing parts at it, I wanted to see what the logical diagnosis path was, and/or if these symptoms point to a clear culprit. Thank you!

 

[1987 GMC Jimmy]

Pull the ICM and take it to Autozone to be tested. If it passes, ask them to test it three or four times if they don’t volunteer to do so. You need a Delco ICM. They cost an arm and a leg at Autozone compared to what you pay online. If for whatever reason it passes, there are tests for the pickup coil and ignition coil, but we’ll cross that bridge when we come to it.

 

[RoryH19]

ICM was my first thought as well.
As mentioned, have it tested multiple times especially since the problem was intermittent.

 

[KCHilite]

Appreciate the advice. I’m heading that way now. I’m afraid I’m going to need a new ICM anyway. The distributor looks newer, but when I removed it from the distributor, the two wires from the distributor to the icm were so corroded at the leads that both tangs came right off the icm with the wires.

I went ahead and pulled the ignition coil as well to get it tested because it looks original.

 

[1987 GMC Jimmy]

I don’t think they test ignition coils, at least not any old style ones. You’ll need to do that with your DVM.

 

[KCHilite]

Thanks for the advice guys, much appreciated. I changed both the ICM and the ignition coil, and she started right up and ran great. Little bit of a stumble/low idle at one point while it was idling in the driveway and it almost cut out---I suspect whatever is causing that may have caused a misfire and killed the ICM before--I'll need to chase that, but otherwise all's well. Thanks again.

 

[1987 GMC Jimmy]

Mine behaved similarly to that; it would stumble really bad when it was cold, and stutter/miss/buck as you got closer to WOT, and it was a bad pickup coil that tested fine on the DVM.