02 Boneville Mis-fire (fixed)
 

Was hoping to get some ideas on what my current issue is with my 2002 Boneville SLE. The car was running fine when all of the sudden it loses power and throws an SES light. I was able to get the car home where I threw it on the scanner and got a P0300 code which is "multiple cylinder misfire". Not much help.

I checked all the wires and plugs which seem to be fine. I just changed them all about 3k miles ago. I'm thinking that this might be an ignition problem of some sort. Is it possible that one of the coild went bad. Anyone else encounter a similar problem? :nm

Thanks in advance.

sense it is multiple misfire and each coil is responsible for 2 cylinders it is very possible that a coil may have let go.or even the ICM

Thanks for the quick response.

When would the ICM be located?

It is directly under the coil packs..In fact the coils mount to it and set on it.You can either take the entire bracket off if that were the issue or just unbolt the icm and coils together from the bracket IIRC it is three 10mm bolts n the bottom..But i suggest testing before removal

Pull off the coils and the ICM, then clean up the surface the ICM is mounted to. Also make sure the tabs that plug in to the coils is clean.

Ok thanks. I have read before to stay away from Bosch plugs. Something about them not working well with the waste-spark ignition system the 3800 Series II has. I replaced the plugs with Bosch plugs before I knew this. Is it possible that this could be my problem?

It could be. I use autolite copper in mine and they work great.

I'm going to pick up some new plugs tomorrow and swap out the Bosch plugs when i check the coild and ICM. Is there a way I can check the coils to see if one went bad?

Here you go. https://www.gmforum.com/trouble-shooting-test-procedures-141/testing-coils-spark-plug-wires-278818/

Thanks! :)

Update:

Okay...so I checked all the coils using the write up posted in the link above. They all checked out fine and were well within the range they were suppose to be as specified in the write up. I also changed all the plugs just to make sure that wasn't the problem either. Still no change and the car is running just as bad as it was before. I feels like it only running on 3 or 4 cylinders and could barley pull itself up my driveway.

Ideas?

Is it posssible that my ICM is bad? I figured if the ICM was the culprit then the motor wouldn't even crank over.

When you pulled the plugs, did any of them look different?

They all looked pretty much the same except one was darker and looked wet from fuel.

Here are a couple pictures:

http://i479.photobucket.com/albums/r...A/102_0086.jpg
http://i479.photobucket.com/albums/r...A/102_0087.jpg

And what cylinder come from, because that's your problem. It's not firing right. Check that plug wire.

It came from #3. I did check all the plug wires and they looked fine. I just replaced them less than 5k miles ago. The car is definately missing on more than one cylinder. It can barley keep itself running especially when you put it in gear. :confused:

You should be able to pull a code and tell which cylinders are misfring. When you figure that out, try swapping two of the coil packs and see if the problem follows the coil pack. You can also test the coil packs, Dan has a writeup on how to do this.

I am a fan of Iridium spark plugs, they cost a little more, but last much longer. Won't work in the SC'd cars, but hold up just find in an SLE. IIRC, your car may even call for Iridium plugs.

While you are at it, check your wires and see if any look damaged. I think I just bought my second set of Bosch wires with a lifetime warranty. I figure for $25 they are worth it, especially if your wires have never been changed and are starting to look worn.

Second on the plugs. It's not that Bosch plugs are terrible, they just weren't built to withstand a waste-spark engine, sort of like hammering a nail with your toolbox.

Check that spark wire, too. #3 on my last set of wires got oiled, burned, and whacked by the fan before it finally started misfiring. There was a flat white spot on it. (Still not quite sure how that all happened.)

Final Update:

So after testing the coils, checking the wires and swapping the Bosch plugs for NGK's and still having the misfire problem...I decided to pull the ICM and take it down to have it tested at Auto Zone. The ICM tested bad so I bought a new one for $136.

After installing the new ICM the misfire was completely gone and the car started and ran smoother than it ever had before. I cleard the SES light with my scanner and it never returned.

I thought that it was unusual thet the ICM would cause such a misfire because everything I read said that the car normally wouldn't start (or run) with a faulty ICM. This of course was not the case in my situation.

Anyway, thanks to those who posted up trying to diagnose my problem over the internet. I really appreciate it! There was a lot of helpful info that led me in the right direction.

Billy

Generally a bad ICM will cause other problems. However, if you have bad terminals that will cause problems with that coil, and it looks like that was the case here. Good deal. I'll mark this thread as fixed.