Can a Bad Coil kill the ICM? - Chevy Impala SS Forum
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post #1 of 20 (permalink) Old 07-15-2019, 06:44 AM Thread Starter
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Can a Bad Coil kill the ICM?

I have an annoying problem that is re-occurring on my 95 LT1. Recently had a ICM go bad based on a "No Start" issue that came up and troubleshooting chart directed me to replace the ICM. I have also been running the MSD 8226 Coil for probably 5+ years without issue til this "no start" happened. Before buying a new ICM, I have a spare (stock) Coil/ICM assembly from another setup that I was able to bolt on and the car and it fired right up. So it sure seemed like the diagnosis was right, a bad ICM.

I purchased a new Delco ICM and installed it (with HS paste) on the same bracket with the MSD coil. The car started right up and ran for about a week or 2 til one morning went to start....and she just cranked and would not fire....DAMN!! Same issue as before and just took a few minutes to bolt on the spare coil/ICM and she started right up again. I suspect I have another bad ICM but these things aren't cheap ($90 on Amazon).

I started to wonder if the Coil itself could be taking out the ICM and found some info out there that suggests this is possible. What do YOU think in this scenario....could the Coil cause the ICM to get fried? Just on a hunch, I decided to replace the coil with another MSD 8226 but looking at this 1 review and the pictures of what this guy found when cutting open, the MSD Coil sure does not give me a "warm and fuzzy" feeling. So instead, I just ordered a new AC Delco Professional coil for about $39 and think this is the better way to go. So again, assuming here that the MSD coil took out a brand new ICM.....does this sound possible and do you think it's best to just stay away from the MSD part?? But check out this review on the Amazon Site for the MSD #8226 Coil and let me know your thoughts. Look at the 1 Star Review from "DYI Man" and the pictures he included. This review is what drove me to get the AC Delco part over another MSD.

https://www.amazon.com/MSD-8226-Blas...ustomerReviews

I also have a Under Load, under power miss that I suspect is a bad wire and will be replaceing the wires with some from taylor that I just got. It almost feels like it's running on 7 Cylinders and just seems sluggish in upper RPM's. Hope to get her running well again soon.

================================================== =============


'95 Caprice SS conversion - Bonny Buckets - 96 Column, Shifter and Console - 3.73 Gear and Herter tune - Z/28 Cluster - Blazer OH Console - Green/Pink bushings - Chromed Impala Wheels - Eibach Springs and Bilstein Shocks - Corvette Engine Dress - the list goes on and still more to do...it never ends.

Last edited by 4DoorSS; 07-15-2019 at 06:47 AM.
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post #2 of 20 (permalink) Old 07-15-2019, 09:28 AM
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V.Good write-up. I've read more than once on here to replace IC and ICM as a set. Call it scientifical, or just urban legend/old wive's tale, but cost v. confidence tilts me to replacing together. And another ENTIRELY subjective insight = car mags since the '70's have been hawking brightly colored and way more attractive aftermarket ignition parts compared to their oem counterparts. But I collected repeat cases where neighborhood friend's running problems got traced to their aftermarket distributors and ignition coils. While I always weighed in at least a small potential for improper installation or fitment, the excess cost over stock steered me just make sure of good maint. of stock stuff in those areas. What's interesting is for the past near-20 years on this forum I've picked up on numerous cases of the same thing for elec. gremlins, - especially regarding your brand in question and the other popular one. Sure, ACD and Delphi and other 'used-to-be-trusted' reps keep sliding, but for the revs most of us run I've never felt ignition is the weak link on a sbc.



Sorry, just a long way of adding support to your diagnosis and suspicions. And I know you know about the dozens of documented "off-idle miss" issues that just may be contributing to your under power problems.
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\'96SS SOB: SSRI, Herter Tune, Tri-Y II, , 3000 Edge, F/HO bars, METCO extendeds with CV MMC, Bilsteins, currently Vredestein Ultrac Sessanta (315/35 rear). Finally, wait for it... LT-4 knock module!
\'96FWB BUW-Butt Ugly White: PCMPerformance tune, HDFA w/ swissed filter, 1/2 SLP s.s. catback with H- and Flow Super 50s, oem opti rebuilt 3 times, SS Bars, METCO LCA, Airlift 1000, Monroe SS, PowerTrax No-Slip, CTS wheels with +1 rubber. Finally, yes again... LT-4 knock module!
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post #3 of 20 (permalink) Old 07-15-2019, 09:35 AM
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Since it only took 2 weeks to fry it, i think using the $39 coil is a good throw parts at it test. You will know soon if your replaced coil was the issue.

-ALF out...
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post #4 of 20 (permalink) Old 07-15-2019, 09:38 AM
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IMHO ICM can effect coil and vise versa. The coil may test fine cold (ohms) but that won't show a broken wire inside the wrap

Also take a GOOD look at the wires & ground terminal on DS head at ICM/coil

I tried ordering the AC Delco ICM from Amazon...they won't ship to CA (customer service did not know why). Got it at RA
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post #5 of 20 (permalink) Old 07-15-2019, 10:01 AM
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In the old days with points I expect mechanics would be able to see a coil going by how bad and how quick the points contacts burnt out.


With the variables of heat and speed diagnostics would be hard. You could patch a current meter into the ICM power line and see if a suspect coil was drawing more current than a new one.(@set RPM and temperature) A logging oscilloscope might show more. But economically a new coil and ICM and a inspection and cleaning of contacts and wires is probably the best way to go.


I have two old Honda twin motorcycles with factory capacitive discharge ignitions. The process is about the same. Replace the coil if the CDI module fails. Ford moved the ICM off the fender and into the PCM while Chevy (same time 1990s) put it on the engine. These parts should be OK with engine bay heat but reality seems like there is a problem.


One mod I never get around to is running a ground wire from the ICM/coil ground to the main ground on the other side of the block.I see many old cars with added ground wires to main components like voltage regulators windshield wiper motors, and ignition modules.

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post #6 of 20 (permalink) Old 07-15-2019, 08:05 PM Thread Starter
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Thanks for the input guys and really hoping it's just the Coil that went and not the new ICM too. Mad at myself for not replacing the Coil with the ICM.
Once I get the new Coil, I'll try to swap out the MSD coil and use the New-ish ICM and cross my fingers. Hate to think I got to buy another ICM but I wont trust my 25 YO Spare setup for the street but it's nice to have a diagnostic spare on the shelf.

I'll let you know what happens and will most likely look at my Plugs and replace all the wires. I've noid checked all 8 injectors and they are all pulsing. I need to get a stethoscope and listen to each injector too but they are fairly new Accell replacements, could be 1 is not working. I also checked for arcing near the plugs and under the car in a dark garage and didnt see anything. So I dunno, could just be a dead plug or wire?

Background/symptoms - Car was running like a top after the new injectors and then the car wouldn't start about 8 months ago. Lots of family, jobs and other stuff and I finally get her fired up with new ICM. Take it on a test drive and notice the lack of power and something must have went bad just from sitting for 8 months I guess. I would best describe it as under power thru all RPM's, but when she upshifts and I keep the throttle steady "under load" I really feel power drop off and car starts to shake slightly until I give it more throttle to compensate. The shaking stops but she is still under power. I just think there is a cylinder down for some reason and a plug read may reveal a lot. MSD Wires have been on the car for many years and were moved over from my old L99 so it's time for new wires anyway.

BTW - Someone mentioned the 4 Ground Rings on the Coil Assembly Bolt. I did check these and cleaned them up again and they're fine. had to re-crimp a terminal on 1 of those wires a while ago that the original ring had broke off.

================================================== =============


'95 Caprice SS conversion - Bonny Buckets - 96 Column, Shifter and Console - 3.73 Gear and Herter tune - Z/28 Cluster - Blazer OH Console - Green/Pink bushings - Chromed Impala Wheels - Eibach Springs and Bilstein Shocks - Corvette Engine Dress - the list goes on and still more to do...it never ends.

Last edited by 4DoorSS; 07-15-2019 at 08:10 PM.
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post #7 of 20 (permalink) Old 07-16-2019, 09:52 AM
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4Door...when I had a plug arc (stumble under load) I also looked and could not see the arc.....until by chance I was under the car with engine running and could hear it and finally found it. #6 plug wire had the stock heat shield over boot and arc was between boot & shield making it VERY hard to see

I have Magnacore plug wires. Very nice but not the cheapest wire set. Got them from Lingenfelter

\'96 BBB 383/T-56
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post #8 of 20 (permalink) Old 07-16-2019, 12:19 PM Thread Starter
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I heard those little Metal shields can be problematic. I have a set of Taylor Thunder-Volt wires to install and will ditch the metal shields and instead use Cloth Heat covers on the ends of all 8 wires that slide over the plug boot.

Is there a way to check for a bad Spark Plug on the work Bench? I will vissual them but wonder if they go bad, do they break internally and I could just check them with a meter.

================================================== =============


'95 Caprice SS conversion - Bonny Buckets - 96 Column, Shifter and Console - 3.73 Gear and Herter tune - Z/28 Cluster - Blazer OH Console - Green/Pink bushings - Chromed Impala Wheels - Eibach Springs and Bilstein Shocks - Corvette Engine Dress - the list goes on and still more to do...it never ends.
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post #9 of 20 (permalink) Old 07-16-2019, 03:28 PM
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RE: wires and the metal insulators. I've put in Taylor on 3 B/D's at slightly larger than oem (I think I get 7.5 or 8mm?), whatever size they still fit the keepers. I reuse the metal isolators at all original locations. No issues with fit on the boot or clearance to manifold, not even with closer bends of headers.

\'96SS SOB: SSRI, Herter Tune, Tri-Y II, , 3000 Edge, F/HO bars, METCO extendeds with CV MMC, Bilsteins, currently Vredestein Ultrac Sessanta (315/35 rear). Finally, wait for it... LT-4 knock module!
\'96FWB BUW-Butt Ugly White: PCMPerformance tune, HDFA w/ swissed filter, 1/2 SLP s.s. catback with H- and Flow Super 50s, oem opti rebuilt 3 times, SS Bars, METCO LCA, Airlift 1000, Monroe SS, PowerTrax No-Slip, CTS wheels with +1 rubber. Finally, yes again... LT-4 knock module!
96 Black is online now  
post #10 of 20 (permalink) Old 07-16-2019, 06:44 PM
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Quote:
I also have a Under Load, under power miss that I suspect is a bad wire and will be replaceing the wires with some from taylor that I just got. It almost feels like it's running on 7 Cylinders and just seems sluggish in upper RPM's. Hope to get her running well again soon.
Have you tried a timing light on all the spark plug wires? You might get lucky and see a miss at idle. I have some clear inline adapters that light when the plug fires. There is also a inline tester that lets you set a spark gap and watch it.


Quote:
Is there a way to check for a bad Spark Plug on the work Bench? I will vissual them but wonder if they go bad, do they break internally and I could just check them with a meter.
Not with a normal multimeter unless they are a dead short. You could connect each plug to the coil and crank the engine. Connect each plug to a roto-tiller or lawn mower and watch as someone else pulls the cord. A little messing around and you could test the plug wires too.



You are sounding like you want to go back to pre 1950s where things were checked out instead of thrown out. I have seen coil checkers, spark plug checkers, spark plug cleaners, and distributor testers. Some would be not hard to make.


Quote:
really hoping it's just the Coil that went and not the new ICM too.
You might be able to see it work with a 12V LED and crank the motor. You could compare it to a known good one by checking and comparing it's voltage out. Again a oscilloscope might show the issue better.

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