2005 P0304 code questions

Anyone have an opinion on the second plug pic I posted? Does that look like a coolant fouled plug or a defective plug? I know the right answer is to run a compression and leakdown test, but until I manage to find time to do that I'm searching for clues (or maybe peace of mind).

 

It does not look coolant fouled to me, though that plug does show signs of being the wrong heat range. The 1GRs I've dealt with that had the telltale blown headgasket issue creeping up had more of a glazed look on the spark plug electrode & ceramic in the affected cylinder(s). Those engines also had the cold-start coolant gurgle noise and cold-start misfires on #6 primarily. Once the head gasket fully lets-loose, you won't need to read plugs or do a compression test to figure it out.

I'd start by putting in some fresh copper plugs, move the coil from #4 to another cylinder and go from there. If you're not having to top up your coolant regularly, at this point I'd suspect it's not a head gasket. Don't let the spewers of misinformation here scare you. These guys live for the opportunity to hoist the head gasket flag on 4.0L owners like a mindless mob anytime someone shows up with a misfire concern. The early design head gaskets do have a higher failure rate, yes, but there's no sense in freaking out about it until it's properly diagnosed as such. Even then? It's just a gasket. You replace it, and move on with life.

 

I agree with @blu92in99

The plug doesn’t look coolant contaminated. I’d throw in Denso plugs and switch the coils to a different cylinder. It’s mostly like a plug or coil.

I would not worry too much until you start loosing coolant. Then I’d run a compression check. Worry about the big stuff only when you need too.

 

Just a quick update; after switching the plugs and coils around the code went away and never came back. I've driven it daily and have gone through several tanks of gas. New Denso copper's are on order but haven't arrived yet. Hopefully it was just a loose connection or something goofy like that.

Thank you guys for your help! It was appreciated.

 

Sounds like you're getting it figured out..

In my opinion one of the best indicators of a head gasket leak is a slow loss of coolant. If the coolant level is not dropping over time then the head gaskets are likely fine

Autolite plugs are trash, get them out of there. I've chased intermittent misfires on a few different vehicles that ended up being caused by Autolite plugs

 

X2.I had a friend with a Honda civic who put in autolite coppers and spent a day trying to figure out a misfire and overall poor running. Switched to ngk copper and the issues vanished. Ive also seen fords and chryslers have ngks put and run like garbage. So cars just work better with certain brand spark plugs. They can be weird that way.