RedLeader289

iTrader: (2)

So, finally getting around to driving my car again. Which brings me back to a gremlin I've been chasing for a long. . . .long time, with no luck.

I think something is eating my ICMs. I thought I had fixed it a while ago. The last one (an AC Delco) lasted longer than all the rest but still failed about a month ago. It did last almost 3 years though, but I could tell it was going to go out when the random hesitation started to come back and lo and behold I was right!

Here's the symptoms: rough idle, hesitation on acceleration, exhaust has a more "gassy" smell than usual

Here's the info that I know:
- The carb is tuned and working correctly.
- The Coil tests within spec.
- The Pickup Coil tests within spec.
- Timing is correct.
- Alternator voltage is 14.6-14.8 when running and still stays above 14 when you turn on the headlights, radio, etc. No voltage spikes.
- Spark plugs are basically new (less than 100 miles on them).
- ICM is new but is NOT an AC Delco (I plan to purchase a couple AC Delco units soon and put one in).
- No signs of arching inside the cap or from any of the wires.

My spark plug wires are physically in good shape, no cracks/melts/burned spots, but are also pushing at least 10 years old. Before I 'parked' the car I tested them with my multimeter and they seemed to be ok. Yesterday I pulled the #1 and #2 wire and tested them and found that the #2 wire has almost twice as much resistance as the #1 wire. . . .even though they're the same length. I think that the cores are starting to breakdown so while I'm looking for NOS AC Delco ICM's at the swap meet this weekend I also hope to pick up a decent set of new plug wires.

Would bad plug wires have fried the ICM by making it work too hard or something?
I know that parts store ICMs are garbage, which is why I plan to put on an AC Delco once I get one but I'd like to figure out why the last one failed.

Looking for any input or ideas on things I can test/check this evening. Thanks!

Tootie Pang

iTrader: (2)

Have you checked the vacuum?

RedLeader289

iTrader: (2)

Oh yeah, forgot to add that to the list - new vacuum advance, no leaks in the system.

OrangeBird

iTrader: (1)

When mounting your new ICMs , if your not going to a computer supply store and buying the good thermal paste that serious computer builders use , that right there could be why your car is eating ICMs . The little capsule of useless pus that comes with a new ICM is just that , pus , trash , and not at all suited for properly transferring the heat away from your ICM .

PS , your ignition coil can pass the ohm meter test and still have partially shorted primary windings , which would increase ICM current (and thus heat) . If the windings are shorted to the coil's frame that is easily found with the ohm meter , but if there are a few sets of windings shorted to each other only , and not to the coil's frame , the small difference in Ohm readings is almost impossible to detect since the primary's resistance is already quite low ....

RedLeader289

iTrader: (2)

I totally agree, I have my own tube of thermal paste. I actually had an argument with the manager at my local NAPA store years ago because they were literally putting dielectric grease in with their ICMs. Didn't know that about the partial shorts though, and tips on checking that?

zed-028

Ill probably be shot down for this but here goes anyway - Even using arctic silver and a myriad of different thermal paste i was chewing through these ICM's like a fat kid eating candy, i chased and replaced wiring and genuine parts forever.

I ended up buying one of these generic ebay distributors https://www.ebay.com.au/itm/CHEVROLE...6acda4b&_uhb=1

2 years of daily driving later and the thing is still as solid as ever. no wear on the rotor, never misses a beat. I also put one on my friends HQ (holden) with a 350 in it, has never failed. I know many of the people on this board hate buying anything Non US, but ill take a working solution over parts pedigree any day of the week..

RedLeader289

iTrader: (2)

Thanks man, I'll keep that in mind. Heck, even ACDelco stuff isn't made in america anymore.

This weekend I cleaned all my grounds, installed new spark plug wires, and still had the same issue. Then (after a tip from my Dad) I did even MORE research and found out that I need to be running a matching ICM with my coil. Apparently the since the MSD coils throw a stronger jolt the ICM needs to be of the same caliber to be able to handle it. Stock units (AC Delco) will eventually burn out and parts-store pieces will basically fail immediately (as I have found out so many times). I found a couple random testimonies of folks being like "I've ran it with the stock ICM and a blah blah aftermarket coil for 20 years in the snow barefoot and never had any issues. . . ." but for the most part the consensus was that they need to match. It's similar to how on the old points distributors you had to put in a resistor after a Blaster Coil to keep from burning up the points.

So I ordered an MSD ICM, should be in in a couple days.

I also am going to put a ground strap from the block to the subframe. Right now I have one from the battery to the subframe and from a valve cover bolt to the firewall.

GeneralDisorder

iTrader: (1)

Yes - if you are running an MSD coil it is *capable* of higher voltage. The voltage it actually generates though will be dictated by the spark plug gap. So unless you are running larger than stock plug gap, the MSD coil is going to output exactly the same voltage as the stock coil. What a performance coil allows is a larger plug gap. Assuming the ICM and other components will handle this of course.

GD