Thread: Car died and then devloped misfire

Just had to tow my 00 GT back home. I'm heading back out to my parents house where I was supposed to be for dinner so I may not be back on till later, but looking for ideas.

Driving normally down the highway and all of the sudden I notice that I have no throttle repsonse. The tach still was reading nomal engine speed for 65mph, and there were no CEL's on, what not overheating, and all my Pro-Comp gauges all indicated normal. Oil was still at 50+ psi. Battery light came on but that was after I noticed that apparently the engine shut down.

Got it on the shoulder and popped the hood. Now since I had a critter chew up the injector harness for cylinder 4 last week I thought maybe it had come loose. It's good. Oil is good (full, not milky, etc...). No external signs of a leak anywhere. All plug wires tight on plugs and coils. Nothing seems out of place. It fired back up on the shoulder but has a miss. The flashing CEL didn't start right away and it seems to smooth out w/ an increase of RPMs. Idle will show a miss and a vibration (obviously). There are no noises that I can here. No clicking, tapping, knocking. Just a misfire.

Can anyone suggest where to start looking for the issue? Usually when something like this happens I have notice. This one literally came out of nowhere. It's been running fine since the motor went back in.

I'm going to pull all the plugs and see what shows there. If nothing is seen there then I have to find a scanner I can borrow to figure out what cylinder is missing. Can't drive it to have it scanned unfortunately.

Happy new year to me, lol.... First my Bonne eats the fuel pump (which is taking my last garage bay now), and now this one goes down

Ignition control module (ICM)

Battery cables tight and clean. I'll be pulling the plugs for sure tomorrow. Hopefully none of them are broken.

I was actually thinking ICM for some reason. Since my tach didn't drop to 0 I ruled out the CKPS, especially since it still runs. Is there a way to test the ICM? I have the one from my original motor laying in the garage that I can swap it with and see if that clears it up if the plugs come back ok.

approx 253K on the car, but only roughly 130K on the motor.

I just finished pulling all the plugs one by one and each of them showed NO signs of damage or fouling. They were all a light gray. The only issue was that the back 3 were a bit overgapped, so I dressed each plug and set the gap.

I did also notice that my coil pack for cylinders 1/4 had 2 cracks in it, one on each side running from the top edge all the way down to the bolt hole where it mounts to the ICM. I replaced it w/ a known good pack and fired it up. It does still feel like it has a miss, but running smoother. The CEL is still on solid and this time I noticed the smell of unburnt gas coming from the exhaust and I only had it running for a total of maybe 20 seconds. I still hear no noises and the oil pressure seems to be good. I thought I smelled that yesteday but on the side of a highway w/ 30mph winds all day as well its kinda hard to track down smells.

Any ideas before I replace the ICM? I really need to get my hands on a scanner and see what the CEL is pointing to. Need this done today as I have to work tomorrow.

Alright, I rented the scanner from Oreillys and here's what I have:

Only code is a P0300- Random Misfire Detected

Freeze Frame data is as follows. Not all of it makes sense to me but may help someone else id this issue...

Fuel System 1- CL
Fuel System 2- NA
Calc. Load- 2.3%
ECT- 183*
STFT- B1 (%)- 10.9
LTFT- B1 (%)- 16.4
MAP- 10.3Hg
Eng. RPM- 715
MAF (lb/min)- 0.613
TPS- 0%

I assume since my TPS is 0% and the RPM was 715 that this freeze frame was caught at idle. I cleared the code since checking the plugs and replacing the 1 coil pack and the P0300 came right back.

And before I forget, as far as I know the cat on there is original to the car. May have been done once but no way to prove it.

Would a clogged cat cause a random misfire code? Seems kinda odd but possible I guess. I'm out of ideas for now so off to replace the ICM and see what I get.

I went ahead and stuck my spare ICM on. Fired right up and no CELs. Let it relearn with a short drive then drove it to Oreillys to return the scanner and get my $445 back for it. By the time I got home it seems to be running fine. No symptoms, no cel. It even seems to drive better than before it died, lol... Probably from me re-gapping the plugs and changing that cracked coil pack.

We'll see what happens after driving to and from work tomorrow. If it won't die in that 100 mi. trip then I'll call it good.

I was kinda wondering if the coil may have fried the ICM somehow. It would explain why I had such a smell of fuel in the exhaust. Other than the $187.43 towing bill I got away for free since I had a spare ICM and 3 coils from my blown up motor. Gotta love spare parts. I have GOT to get my Bonneville running again. Messing w/ this all day out in the cold w/ the strong winds was a b*tch, even with insulated coveralls on.