Another misfire thread

[Mooseman]

Well, today I was tackling a loss of 2mpg, which coincidentally happened at the same time I put in my tuned PCM. After two tanks, I went from 17mpg avg. to 15mpg avg. Hooked up the Tech 2 to check things out. I did a code check and got a p0300 (random misfire) but it didn't set the CEL. Hmmm. So I swapped the other stock PCM back in and still getting the misfires. Went to misfire counts and I was getting the odd few misfire on cyl. 4. Not a lot, maybe one every 5 cycles or so.

So figured I'd start with the usual diagnostic step of swapping the coils. (4<>2). Misfires stayed at no.4. Swapped the tuned PCM back. Same deal.

Engine was hot so I didn't want to chance pulling the plugs and tonight I'm working. Figured I'd just throw in some new plugs anyway so I ordered a set from eBay (great deal). When I swap them out, I'll probably do a compression test at the same time.

So just to recap:
- PCM not at fault
- coil not at fault

Next steps will be:
- do compression test
- replace spark plugs (ACDelco 41-103)

 

[Reprise]

Didn't see reference to swapping the plug wire on #4. If you have some dielectric, try applying that to the wire / plug connection. Long shot for a permanent fix, but may help track down the issue or fix it temporarily.

 

[Mooseman]

No wires. This is on the 4.2 so it was a coil swap. Could also be done on a V8 too I guess to eliminate that.

And an update, on my way to work, no misfires. And the plug well was bone dry. Anyway, unless something else happens, next update will be when I change the plugs.

 

[JimInRadfordVA]

This post is relevant to my interests!

I've had an intermittent misfire at all RPMs with no CEL for about two weeks. CEL finally popped two days ago. Had it read and it shows a P0306 - Misfire on #6 cylinder.

Until I can dig my scan tool our of my garage (still haven't recovered from a recent move) swapping the coil pack will require going to the local O'Reilley's to have it read. I'll start a separate post and keep you all up-to-date on what's up. Might be a good time to send my PCM off to NC!

 

[Mooseman]

I have a slight update. Monitoring the misfires and it seems to be more prevalent only on warm restart and idling in P or N. Once fully at operating temp or in D, they drop to almost nothing. On cold start, nothing. Again, still just on cyl.4. Engine running smoothly and not enough to trip the CEL or a hard code.

Still waiting on plugs. They're in KY now, shipped from OR. Go south to go north.

 

[JimInRadfordVA]

Where did you order from?

 

[Mooseman]

Posted above great deal

 

[linneje]

I am pretty sure you are looking at $150 or more getting these (6 of them) in Canada from a supplier or GM dealer.

 

[Mooseman]

Yup, which is why this was a great deal, even with shipping.

 

[littleblazer]

Flakey injector causing it to randomly be slightly rich on 4?

 

[JimInRadfordVA]

Posted above great deal

Excellent. Just ordered a set. Thanks for the heads-up!

 

[Mooseman]

Flakey injector causing it to randomly be slightly rich on 4?

Quite possible it's having trouble regulating fuel flow at the lowest output.

 

[littleblazer]

Quite possible it's having trouble regulating fuel flow at the lowest output.

I've been dealing with lots of injectors lately, so for now that's where my head goes.

 

[JimInRadfordVA]

Standing by for an update.

 

[Mooseman]

Received all the stuff. Just haven't had the time. Work and things to deal with. It still has the odd misfire that can't be felt but seen only in Torque.