ICM Diagnosis/Misfire

[Finallyflying]

A couple weeks ago my 2001 LeSabre was idling for about 30 minutes on a very hot day (temps close to 100) although the coolant temperature didn't go over 215. It began running rough while idling (chugging/chuffing) and I noticed a soot stain on the pavement under the exhaust. I was able to drive it home (about 9 miles) but clearly it was not producing full power and idling very rough although it never quit running even at idle.

A scan revealed a P0300 code and substantial misfire on companion cylinders 1 and 4. I verified no spark from either coil tower with a spark tester, and then I swapped the 1/4 coil with the 2/5 coil and the misfire did NOT follow the coil...it stayed with 1/4 even with the 2/5 coil plugged into that spot.

Next, I ran through the ICM diagnostic procedure at the connector referenced in another post on this forum and verified the following per that procedure:

1. 11.9 volts present at the P-wire
2. 11.9 volts present between the K-wire ground and battery positive
3. 10.8 volts present at the N-wire to the CAM and CRANK sensors
4. At the G-wire, I rotated the crankshaft with a socket wrench on the crankshaft pulley bolt (after pulling the fuel pump fuse) by one complete revolution and counted exactly 18 6.3 volt pulses and finally,
5. At the H-wire, I counted exactly 3 5.7 volt pulses in one revolution.

Is there anything else I should check before ordering a new ICM, and while I'm at it, should I go ahead and replace the 3 coils? Just thinking that with 24 years and 125,000 miles heat and time are probably taking their toll on them as well.

Thanks!

 

[Finallyflying]

So I replaced the ICM and that did solve the 1/4 misfire problem. The learning point for me is that an ICM failure can look exactly like a coil failure if it affects companion cylinders. Swapping coils around can verify that the coil is good, and once you know that the ICM is getting voltage, ground, and a good crankshaft position signal, then the only thing left is the ICM.

Regarding whether to replace all the coils too or not I think is dependent on how the car is used. If it were mostly local trips fairly close to home, then I would probably run the coils to failure. However, most of my trips are interstate, and because of my work schedule frequently very late at night/early morning. A failed coil in that situation is more inconvenient, so I decided to replace all 3 coils along with the ICM. Original GM coils really weren't that expensive online compared to the aggravation of one failing far from home.

 

[Buick City Bert]

Had a bad experience with an after market ICM, after that I only by OEM ignition components, and sensors.

 

[Finallyflying]

Had a bad experience with an after market ICM, after that I only by OEM ignition components, and sensors.

Yes, same here. There’s so much cheap stuff on the market these days. Those $20 parts are tempting until it leaves you on the side of the road 3 months later 😂

 

[jotzgr]

The sad part nowadays is that it doesn’t matter if you spend two or three times as much for a name brand; you’re probably getting the same cheap Chinese s**t that’s $20 on Amazon. I have 14 vehicles and believe me, it really doesn’t matter what brand you buy or how much you spend, it’s all cheap China junk that doesn’t last. I usually compare closeup pictures side by side and they are usually identical in all the markings. Sad state of the world today . . . I try to look for Made in USA but that’s few and far between. I’ve bought older NOS stuff just because it said Made in USA or Made in Canada and had somewhat better luck with that.

 

[02LTD2.0]

I've had good luck with aftermarket coils but as far as an ICM I would always go with the OEM.

 

[gmtech 2019]

If you can’t find an oem part the next best would be a used one at the car junk yard. Look for a car that had collision or rust that caused the junking of it.