Years ago, I started to get this intermittent miss when I would roll into the throttle. Like all 8 cylinders would just "drop out" for a split second. I looked and looked but never could track it down, and it started at about the same time that I put in the 383 with HSR and C950 ECU. After about a year of going through all my ecu settings (ie acceleration enrichment) along with other things.. I couldn't come up with a fix and finally stopped worrying about it since it didn't cause much of a problem. Then recently, started having a no start issue. Couldn't exactly ignore that obviously, so I assumed it was the ignition module, so I picked up a new ICM and pickup coil for good measure, and decided to completely remove the dist. and tear it down. As I was cleaning up the pickup magnets with some scotchbrite, I noticed that some of the "stubs" on it started breaking off, (you can see them in the pic). So not wanting to put it back together while not right, I bit the bullet and tracked down an A/C delco magnetic pole piece assembly. It includes the whole shaft that goes down to the dist. Anyway, it never occoured to me that this could have been the problem, but after changing the pole assembly and pickup coil, I noticed that it wasn't missing anymore. So I guess I got a 2 fer. Fixed the no start prob and miss problem at the same time.

 

I had a similar, but different issue. once I dropped in a 350 block that I found for $75,I ran into acceleration issues. The IROC idled fine until I would give it some throttle. It would hesitate like crazy. I twouldnt go over 1,000 rpms because it would begin to backfire like crazy. So over and over me and my uncle switched ECM's, checked the timing, diagnosed the fuel system and nothing. I was ticked off to the max. So I decided to replace the whole ignition system, mainly the dizzy. I pulled it out and dissected it down to the core. Now once I removed 3 little bolts that hold in a little circular magnet (pic. below), it literaley fell into pieces. The magnet was broken into 4 pieces. So I replaced that and the pick up coil and VVVVVRRRRRROOOOOMMMMM. She was good to go!!!!!

 

I have seen and diagnosed so many faulty distributors. Many, many years ago when I was still using a large cap HEI in my car, I went to the auto wreckers to pick up an assortment of weights and cams to play with the timing curve. When I pulled the cap off on a second gen, the weight pins were completely worn out. All I could think was the last owner probably thought the car was a POS because it never ran right and all he needed was a new distributor.

I've also found many crack or broken wires to the pickup coil. Engine runs fine and accelerates fine but a slow acceleration with a part throttle always gives a hesitation miss. The cam plate is rotating with the vaccum advance and opening the cracked pickup wires causing a lack of spark. When the rpms drop, the pickup plate drops back and spark is resumed. Under hard acceleration, the vaccum advance plate doesn't rotate. That was a fun one to diagnose.

Those 30+ year old distributors need to be thrown out. They don't last forever.

 

Glad to hear you got it fixed. Look at the mag pickup as well while you're in there- they can get cracks in them too. And make sure you have the pickup properly centered around the center tooth wheel before you put it back together. Rotate the shaft by had and make sure none of the teeth are clunking against eachother at any point in the rotation. That can be a touchy adjustment.

Agreed with AlkyIROC. I keep a spare known-good small cap computer controlled HEI in my garage (actually, I've got one of just about everything). If I'm getting weird behavior that I can't track down quickly with the usual cap/rotor/plugs/wires fix I stab in my spare to see if it makes any difference. Many times it does. I gave up fixing old distributors one piece at a time long ago, mostly becuase pulling the shaft out of a high mile distributor is very difficult in most cases (oil gunk builds up on the shaft and makes it near-impossible to pull it up through the top bushing).

 

Small cap HEI? My 86 uses the large in cap coil. Is there a large cap hei/remote coil and adapter wiring for the large 4 pin harness?