So i recently acquired a 2001 XJ. It drove fine for the 30 mile drive home. The next morning it wouldn't start. Bad battery. I replaced the battery and then started getting a P0302 code. Sometimes the cel would flash but then it would stay solid. it would usually flash after about 15-20min of highway driving when exiting and slowing to a stop. And occasionally it would throw a P0305 and P0300, but not always. I have replaced the plugs with Champion Coppers. it still comes back. I ran sea foam through the intake thinking that maybe it had some carbon build up. The engine runs a little smoother now but still throws the P0302 code. Today i replaced the #2 injector, thinking that maybe it was a leaky injector. I also replaced the valve cover gasket and while i was in there made sure that all the valves moved. after all this it ran fine until i got stopped at the gas station and filled up. maybe a two mile drive. after the fill up i pulled out of the gas station and the cel popped back on. P0302.

I am currently at a loss. this is my second xj but the first one i didn't own for long and the biggest issue i had with that was the p/s pump went out. I'm not sure where to go next here. coil rail? not sure how to test to see if that is bad.

the oil is clean and its not comsuming coolant. it has a small exhaust leak. its currently has a 3 or 4" lift running 33x12.50r15.

i have searched for that last few days but not really sure where to go next.

Please help.

 

Need to start ruling a few things in or out.

I'd personally start with a fuel pressure test (49 plus or minus 5 is your spec.) and a compression test (120-150 with no more than a 30 psi variation between cylinders; run dry test, then wet test if any cylinders are suspect).

Good luck and keep us posted.

 

Thanks for the quick response. Ill go do those tests later today.

 

With all the random misfires you're getting, I'd check your coil.

 

His Jeep has coil packs.

 

Also your Jeep calls for different plugs. Look under your hood and check the sticker. I am pretty sure it calls for NGK.

 

So I ran a compression test and #5 came up with 50psi. So I did a leak down test on #5 and air was coming out of the throttle body. So I think I have a valve sticking. Or at least some nasty carbon build up. I ran some seafoam through the engine this morning but it still idles rough. No cel yet since the smoke cleared, but I haven't really had a good chance to test drive it. Correct plugs according to the sticker under the hood.

Thoughts? Ideas? If I do need to pull the head what else should I be replacing maintainence wise?

 

50 PSI is really low. Check the valve and go from there.

 

If you have a 301 head, they are prone to cracking issues.

 

How can I tell if I have a 301 head?

 

Oops! My bad. It is 0331 head. I am pretty sure you have it.

 

Where do they usually crack? And if it was cracked wouldn't it show up else where on a leak down test? Or burn oil or coolant?

 

The 2000 and up to 2006(I think) 4.0 have the head. The number is on the driver side middle of the head.

 

Yeah, I would say you would be loosing coolant.

 

I am not too sure where they crack. Sorry.