P0302 Code Multiple times now

[d-wreck08]

Hello, I have another interesting issue I would like to get some input about.

A month or 2 ago, my envoy started to misfire horribly, only for a short while and only this once, the CEL was flashing at first but did not stay on. A week or 2 later the same thing again, but this time the CEL stayed on. Took it to Autozone to have them read the code for me and it came back with cyl 2 misfire . I read up on this and found swapping spark plugs was a good place to start, since I had no idea when they were replaced last. Pulled them out, and replaced them(Delco 41-103), while I was in there though I decided to switch the coils around to see if I could pinpoint that as a problem(if the code moved to cylinder 1 it would know what to replace next) Below are some pics I snapped while I was in there, seems to be some sort of little build up on the ignition coils that I thought looked suspicious. I do not believe my envoy has the extra weather stripping in it yet to prevent water getting down on cyl 5 I believe, that that coil does not seem to be the problem though, and actually visibly looked better then some of the others.

Another few weeks passed with no problems, and then it happened again...CEL stayed on, so I stopped in to see what was causing the problem this time, same thing P0302 cyl 2 misfire. I'm somewhat at a loss of what to try next and could use any input. I'm about to run some sea foam thorough every safe part I can but have not gotten to this yet.

In addition I have noticed this really only seems to become a problem after it has warmed all the way up and I turn it off for 30-45mins and get back in to go somewhere again. It has a terribly rough idle at low RPM's but speeding up smooths things out pretty quickly and then it is smooth sailing again. I also have had the dreaded hesitation all the time upon taking off from a stop, not sure if it could be related at all or not, after looking that problem up on here I have just decided to let that go for now until I have some real cash to throw at that problem.

 

[CaptainXL]

What Brand and octane fuel do you use? How many miles are on engine?

 

[d-wreck08]

I typically filled up at a Lassus Handy Dandy but recently moved and have been filling up at Marathon or United Dairy Farmers or Speedway a few times.

87 octane every time as per the owners manual if I recall correctly.
Currently just shy of 160k miles.

I've only had it for about 12-15k miles myself, when I got this last year though the carfax report was over 5 pages long, even with multiple owners it never really seemed very neglected, as all of the carfax stuff was usual maintenance, nothing to crazy anyway.

 

[RayVoy]

If you let a mis-fire go (and the CEL is flashing) without servicing the problem, you stand a real good chance of damaging the cat.

When I had an Envoy with the I6, I had the mis-fire problem a couple of times, I was always able to fix it by replacing the boot that covers the high voltage spring between the coil cap and the top of the plug. Under the right (read wrong) conditions, the spark will run down the inside of the boot to ground (actually, it runs from the ground to the coil, but that's a different story).
Take a look at the inside of the boot, look for a carbon path from end to end. A new boot is not very expensive.

BTW, you probably know this, but plug number one is the front plug.

 

[d-wreck08]

Thanks for the info RayVoy, I think that would be good place to start as well, restively cheap and not difficult. I do have a quick question about doing that though, would doing all 6 be unnecessary or a smart place to start?

 

[eman]

I've been having the p0302 issue for a year or two And would love to collaborate to get both solved. I've replaced the boot #2 and all plugs last year among other things and haven't been able to get it resolved. I've run injector cleaner every half year or so and same issue, haven't tried sea foam yet.
I keep a scanner in the tb and whenever the CEL comes on I check it and its always the p0302 so Clear it. seems like its about every week or every other week that it throws this code. The p0302 seems to throw the CEL more often at an idle in my TB, what about yours?
Very interesting about the grounding issue ray-voy mentioned. i know bad grounding in these trucks can cause major issues, had that before but the truck would stall. I've been wondering if there is bad wire going to the pigtail on boot #2 or a short in the pigtail which could be causing it to throw the code.

 

[d-wreck08]

eman

Mine only throws the code at low RPM, never just cruising the highway, in fact speeding up has always smoothed it out within seconds. Mine has also only just begun to do this, in total I think 3 or 4 times. You do bring up a few interesting points, though I almost think a compression test will be on the todo list for me since mine seems to be somewhat dependent on the temperature of the engine. This is only my best guess though.

 

[RayVoy]

would doing all 6 be unnecessary or a smart place to start?

I Don't think all 6 would be necessary, just the one throwing the code.

Very interesting about the grounding issue ray-voy mentioned. i know bad grounding in these trucks can cause major issues,

Sorry, I'm not talking about grounding issuses, I was talking about the high voltage finding a path to ground without going through the sparkplug. Every time a coil fires, current goes to ground. It should go through the sparkplug, but it will always take the path of least resistance (the gap in the plug is very high resistance). If there is a carbon burn on the inside of the boot, the current will folow that path to ground.

I almost think a compression test will be on the todo list for me

This would be my next suggestion if all appears good with the boots.