Engine Error code P0302

[OzRick25]

40,000 km is not a lot (I've got 150,000 km on my factory plugs, what plugs did you use?
There have been a few dramas with premium plugs not being right for the coil. If you've still got old factory plugs I'd give them a go.

Also why did you decide to change them in the first place? And what does cylinder 2 plug look like compared to some of the others?

Does it sound like it is running well despite the code?

[pete 56]

Hey OzRick25, yes I thought these kind of plugs were supposed to last a real long time. I changed mine cause I didn't know the history of the jeep (bought from a yard) & was going for a drive to Uluru, so it thought it a good idea. NKG Platinum? Sound possible.
Not running well when idling, running rough. Once it gets moving seems ok unless the revs aren't high enough for the gear it's in. Still driving it to work, about 15 mins on the hwy at 80k, all good (I hope).
Haven't actually pulled the plug out (quite awkward from memory) will do so as soon as I get a chance (working lots at the moment) & see how it looks.
I was thinking if there is spark then it must be the plug or is it wrong to assume that?
Thanks for your input...


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[OzRick25]

That's a fair enough reason, was just trying to eliminate the possibility of covering up a different issue earlier.

I think MightyMouse has been running the NGK single electrode platinum plugs without issue but that doesn't mean they won't cause problems for others. The problem was with multi-electrode plugs particularly Bosch but possibly others.

Inspect the plug and it should give you some clues as to what's going on. There are quite a few you tube videos about diagnosing faults off spark plugs so have a look. Try and pull at least another one to compare with.

There are quite a few things a miss could be from (valve not seating, scored cylinder, badly worn rings, injector failing and under or over fueling) but hopefully it's just the plug, lead or coil.

[pete 56]

Thanks again Rick, will try and pull a plug out this arvo between shifts (busy day) & have a look at YouTube see I can come up with something,
all the best...


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[Banshee]

I have spare leads if you want to try a different one, as I swapped mine out a couple of months ago when I had to replace an injector.

I think I have some spare plugs (old ones), as well.

[NTRubicon]

In the 3.6 I recently had this same error. After doing the diagnostic workup to figure out what it might be, from spark plug, coil, lead and up, I came down to a faulty coil, and off to the dealer it went. Turns out the PCM had been damaged as well as the coil, and it required replacement of the two parts. I purchased a spare coil to carry in my 'just in case' pack as it was a major inconvenience having my only car off the road for a week waiting for parts (remote areas are not always awesome places to be)

Good luck getting to the bottom of the problem, and get yourself out to the Rock. I'm heading there next week for xmas with the family.

[OzRick25]

Just because you are seeing the lead earth out it doesn't mean it's not the lead or coil because the coil/lead might be providing some but not enough energy and also leads can break down and work intermittently in different positions. If it wasn't earthing you could say it's definitely either the lead or coil. Sometimes damaged leads will work bent or strait but if you move them they wont. If you've got an automotive multimeter you can test the resistance on the leads in different positions, and also for primary and secondary resistance on the coil.

I personally would try and avoid driving it as much as possible until I'd pulled the plug and checked it and got it sorted. Unfortunately there have been a few people that have had coil issues concurrently with pcm issues and it's difficult to say which leads to the other.

If the plug looks the same as the others your probably looking at a new lead and/or coil (rockauto). If it looks different from the others run a compression test (prudent to do this even it looks the same). If your compression test comes back >140psi you've got it down to injector fault or still possibly plug lead or coil so you either test them or just replace them.

Hooking up with Banshee could be the go to check that lead.

Hope that helps some. best of luck.