P0305 or P0300

[SlugSlinger]

Compression test it, then leak down test it. That's some nasty looking crud in there though. Might be valve stem seals leaking too. If it's a coil pack motor, swap a coil with a known good cylinder and see if the misfire moves.

I replaced the single coil pack, plugs and wires first thing. It was no doubt in need of those refreshed. I’ve also ran some cleaner through it to get rid of the carbon build up I suspect is coating the valves.

It has not used any oil since I changed it 1200 miles ago.

 

[SlugSlinger]

I am going to try this to see if there’s hydrocarbons in the coolant.



And O'Reilly has the test kit they loan for free.

https://www.oreillyauto.com/detail/...00290/2008/jeep/wrangler?q=Block+tester&pos=0

 

[SlugSlinger]

Well, I ran the test.



And, unfortunately, it appears to have hydrocarbons in the coolant.

 

[swampratt]

Late to the game I was going to say that is moisture from water or coolant as it is beaded up. fuel with water makes water bead up. But water beads up on it's own.
Fuel will evaporate or lay very thin and droplets of water will remain standing tall.

Water will also clean the top of a piston to shiny clean aluminum as will E85 but conventional gasoline fuel will turn it yellow or black.

 

[SlugSlinger]

The heads are at the machine shop that my buddy owns. He said the layered head gaskets used on many manufacturers engines are bad about leaking after temperature changes. He said they will leak between the layers. Mine seemed to leak after the motor cooled. They seemed to seal when running and warmed up.

Anyway, the shop is going through the heads checking everything, hopefully no cracks, and probably doing a multi angle valve job and cleaning up the ports, not sure to what extent, but heads are one of his specialties. Also installing all new valve seals.

 

[SlugSlinger]

Both heads failed a leak test and had visible cracks.

This is an image of a crack that went under the valve seat.

We found 2 cores that were pressure checked and that the machine shop cleaned up. He did a multi-angle valve job and that looks great.

He surfaced the mounting surfaces and blasted everything and ran it all through the jet washer.

The machine shop did a great job and these are ready to go back on, hopefully tomorrow.

 

[Snattlerake]

Well now you know what it was. Add a cam and rip it.