jcollege

Well dropped my XJ off to get an emission done, and as luck would have it she throws a CEL while the guy is driving it from one shop to another (since his emissions machine went down). I pick her up and pulled the code P0300, she is driving fine no stumbling, so time to begin the search of what it could be. I have read many threads that it could be the CPS, any other quick checks I could do?

tacklebox

I recently had that code after doing a complete tune up. It was the dizzy.

Waynerd

What year? Could it have been heat soak?

jcollege

2001, I was thinking the same thing about the heat soak as well, I know mine doesnt have any heat shields along the injectors...fingers crossed it is that easy

jake92

01? Check Compression on the cylinders

If compression is fine:
Check for spark. Is it blue or yellow? Is it even present?
When was the last plug change?
Check fuel pressure
Check for vacuum leaks

jcollege

I replaced the head about 2-3k miles ago, at that time I did all new plugs, so thinking it is not the plugs, but in the top 5 of the things im going to check first.

tjwalker

P0300 is a code for "random / multiple cylinder misfire". Because a particular cylinder isn't noted in the code, the first thing I check for this code are things that are "common" to all the cylinders.

And that starts with fuel pressure. Easy to do and has to be ruled in or out early in the process. The fuel pressure for the 2001 is 49 psi, plus or minus 5 psi.

Good luck and keep us updated!

EatonXJ

Here is a good read on heat soak http://www.naxja.org/forum/showthread.php?t=1065004

Mine a 2001 throws that code when it happens. Seams like it gets worse every year. It's already happened once this year. I agree with the guys in that thread. Those 2 extra cats cause alot of heat. I'd bet more heat each year as they get older and more clogged up.

Waynerd

Mine has the heat shield around injector 3. Still happens. Did it the other day when it was in the 50's. I was discussing with someone in a different thread recently about the '00 & '01 running warmer altogether. Hopefully that's all it was.