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Discussion Starter · #1 ·
Hey all, I have a few questions I hope the great minds on this forum can help with. 2008 Grand Prix, all stock, well maintained 166,000 miles, engine was running great until about three weeks ago. Started up and ran down my driveway fine as always, but suddenly lugged and sputtered horribly when pulling out onto the road. I just backed it up to the house and started troubleshooting. P0300 code was set, only had a simple reader at that time, so no live data. Long story short, an LED test light found that the ICM was dead on the 1-4 terminals. Bought a new ICM (don't know what brand, was bulk packaged from eBay, looks like an SMP LX364T) and installed it, motor ran much better, P0300 didn't come back after clearing, but it was still missing some.

I found it hard to believe something else was wrong, as I had already checked many things before determining it was the ICM in the first place (~55 psi on schrader while cranking, ~5K resistance on each coil secondary, pulled and cleaned MAF, Delco iridium plugs and wires changed about 6 months ago - original plugs had looked almost new!). Everything checked out fine! I bought a bluetooth scan tool to help, and everything on there seemed fine, too. O2 sensors' voltages vary from 0.1v to 0.8v, MAF reads ~7 g/sec at idle, ~10 at ~1000, ~15 at ~1500 and ~21 at ~2700, fuel trims seem fine, etc., but I don't really know much about what these data should look like, outside of a couple of days of googling. Misfire data shows 25 to 100 misfires on all 6 cylinders (most on 6) after about 10 minutes of testing.

Out of desperation I decided to put the OE ICM back in, and misfire data after several minutes shows the expected 1600 on cylinders 1 and 4, but 0 (that's ZERO) on the other 4! Does this tell me I got a bum ICM from eBay, and there's nothing else wrong? I decided to take both ICMs to AutoZone for their test, and OE failed (of course, said power circuit or something like that) but the eBay one passed! The employee repeated the test 6 or 8 times to heat it up, and it passed every one. How accurate is their tester, i.e. can it detect a small misfire rate like 10 per minute?

I grabbed some screenshots of live tests that I would also like help on. I started each at idle, increased RPMs to about 2500 and held for about 10 seconds, then let return to idle. They are each looking at the manifold absolute pressure, timing advance, and short term fuel trim, respectively, all with the eBay ICM installed. I think they are all as they should be, but I just don't have enough experience diagnosing to know for sure. Especially the way MAP rises as RPMs rise, returns to a baseline as RPMs hold, then drops as RPMs fall, and again returns to a baseline at idle.

On the ICM, I wonder if the eBay seller has seconds or rejects, since they are in bulk, not retail, packaging. They have sold over 700 of them, with no negative feedbacks (but less than 90% recommend as good value/quality) from these particular ICMs, but sell them at $54 free shipping. It did pass the AutoZone tester, but again I'm not sure of the sensitivity of the test. Comparing my OE unit with pictures of ICMs on rockauto, it looks exactly like their Delphi unit, down to the font style and location of the cylinder markings, at twice the cost I paid. AutoZone has their Duralast brand (which is Wells?) with a limited lifetime warranty for three times what I paid, but available at a local B&M. Is an ICM one of those components that you just have to buy a trusted brand, or even OEM, from a trusted retailer to know you are getting a good unit? TIA for any help.
 

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When it comes to sensitive electronics, you need TOP SHELVE PARTS or perhaps a GOOD USED ONE(but that's iffy at best). I would also suggest trying DORMAN PRODUCTS. They make/sell oem duplicate parts and over the years I've used their products their products are as good and perhaps BETTER than the oem. BRAND X OR USED IS NOT A GOOD IDEA.

On another note, did you try moving the coils from one position to another to see if the misfire changes to a different cylinder? If the miss fire doesn't move with the coil swap, your ICM may be bad. By the way, are you sure the plugs and plug wires are good? You may want to test the plug wires for problems also. Try some of this and see how it goes............ Jake

One last thing, test the plug wires for resistance...... or use a spark tester to confirm all the cylinders are getting ignition spark........
 

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Discussion Starter · #3 ·
Hey Jake, thanks for your reply. Yes, swapping coils around was one of the first things I tried, and the missing didn't follow. I then performed an LED test on the ICM and indeed the first terminals (cyls 1-4) were not triggering, and the other two were.

I got the scan tool after this test, and it confirmed massive misses on cyls 1 and 4, with zero misfires on the other 4. With the replacement ICM, it still runs rough, and the scan tool reports 25 to 100 misses on EVERY cylinder. After swapping back in the OE unit, it's back to only misfiring on 1 and 4 with zero on the other cylinders. Nothing else seems amiss (pun intended :) )

I'm just wondering if: 1) this is telling me the ICM is the only problem (zero misses on non affected cylinders with the OE ICM), 2) you can have an ICM that passes an AutoZone test and still be flaky.

I'm threatening on getting the Duralast with the limited lifetime warranty. I'm just not sure if I get a replacement from the eBay seller it will perform any better. I was looking at an excellent review of a Delphi unit on Amazon, and his first one went out after about 5k miles, second after about 8k miles. Bought a Duralast and made it 50k miles and 2 years before it gave out. At least he was then able to get another replacement under warranty!

And I don't think Dorman makes ICMs...
 

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Discussion Starter · #4 ·
Just to update, I purchased a used ICM from a junkyard for $20 and it works perfectly with no misses. I'm returning the apparently defective unit to the ebay seller.

Now the AIR BAG indicator is illuminated in the IPC! :icon_sad:
 
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