Z-28 Won't Start - Ignition Module

[pcitizen]

Evening....

I've posted here before and got precise remedies for my neighbor's Z-28. Thanks. Here's another related to my previous post.

My neighbors Z-28 with a crate engine would not start. You guys said replace the ignition module. Badda-bing... started right up. It was running great for about 15 minutes then... badda-bow... it stopped. I checked the iginition module. The new one was now bad. So I put in another new one in. Started right up... ran for a bit and bingo... burned it out too.

So I am at a loss. What could be causing the ignition modules to burn out. I checked the electrical system. I don't see any shorts or frayed wires. I also checked the wiring schematics. The schematics don't show that a ballast resistor is used. This good... since I can't find one. Is there supposed to be one though? The previous owner really gurred up the electrical system in this car so it's hard to tell what is what some times.

The owner has spliced the electric choke wire which is supposed to be 12V into the BAT terminal on the distributor cap. I don't believe this to be the problem. Not being a Chevy guy, I am not sure.

Advise please.

[wrightz28]

hmm,

You're coating the bottom of the ICMs with silicone to prevent over heating right? And they are AcDelco ICMs?

I would also find another 12v source for the choke.

[pcitizen]

Suspecting that the choke connection could be related, I had disconnected it from the system. I was using the silicone gel as recommened. I believe the parts we've been putting in there are Sorensen.

Seeing how this is the only thing that doesn't match your comments are you recommending that only AcDelco parts will stay working in this application?

PCitizen

[wrightz28]

Well, I'm not saying they are the only that work, but I have seen the wells/GP sorenson ones fail dramaticly quick, not 15 minutes quick tho.

[hazzzmattt]

you didnt mention a model yr but i'll assume this thing is an antique. i remember seeing this problem in the early 90s. the problem was caused by a bad ignition coil mounted in the hei distributor

[pcitizen]

Suspecting a short in the coil it was replaced soon off. The second ICM failed with the new coil. So... could be that the Sorensen part is cheesy or the new coil is truely the culpret... or both.

PCitizen

[hazzzmattt]

i still think youre in the right area. the only other time ive seen this problem on going module failure was on a chrysler product. it simply had an arcing plug wire. the problem is in the secondary ignition. go back over the cap, roter and definately the ignition wires. you dont always see a problem with these componants. its best to put this thing on an oscyloscope to find a jumping wire. that coil will generate how ever much voltage it needs to to find a ground and believe me, its enough to damage electrical parts.

[hvypdl]

• Are you sure it's actually frying them? Maybe it's one of those intermittent problems? How are you checking them?
• It only takes a few more than the specified 12VDC to fry automotive electronics. Check your alternator too. Make sure you aren't getting any AC (alternating current not air conditioning) voltage coming off of it. You may think I'm nuts, but it is called an alternator for a reason. It has to rectify (convert) back to DC and sometimes they go bad (though kinda rare) and fry electronics and batteries. "Dirty DC" as it is sometimes called is a killer for all DC electronics. About six months ago, I had a battery charger do exactly that and fried a brand new battery - and no, I didn't hook it up backwards. Luckily the ECM or any of the other high dollar electronics on that Cadillac didn't fry. I am thinking that's probably because the battery would have acted like a filter or maybe my gaurdian angel was working over-time. A battery is basically just a wet capacitor, right?. Anyway, the stupid thing popped both covers and spit boiling acid all over my engine compartment as I pulled into the parking lot at work. What a mess.
• What condition is the rest of the distributor in? I wonder if really bad spark scatter could cause that. On an old style HEI, the module sits under the rotor... Just to be safe, change the cap and rotor if it's even just a little bit old.
• Don't forget to check the plug itself. Sometimes the wires break inside the plastic and are hard to detect visually. If you have a good meter, check to make sure all wires have resistance when disconnected. Just the other day I discovered a bad plug on my '94 Z-28's module. You couldn't even see a break in the wire.
  Gotta go find some shrink tube and solder to fix that as a matter of fact.

-Good luck.

[pcitizen]

Thanks for all the tips. The ICM was replaced last evening. Once in the carb and timing were readjusted. It is running great.

About checking the parts: We had them tested at our local parts supplier. The original one tested bad after being hooked up for a couple minutes. The other two tested bad right away. The latter were Sorensen products.

[hvypdl]

COOL. I'll have to file that one. Never heard of that happening before. I am used to dealing with industrial PLC's which are electrically (optically) isolated. Glad you got it figured out.

[wrightz28]

Originally Posted by hvypdl

COOL. I'll have to file that one. Never heard of that happening before. I am used to dealing with industrial PLC's which are electrically (optically) isolated. Glad you got it figured out.

Definately file it, when it comes to the ignition system, don't cheap out, get AcDelco, it's worth the extro $.