Jobxj

Bought my 00 xj sport a month ago with 212000 on it and cant shake the cyl 1 misfire code. Just did a compression test on cylinder 1 and got 0 psi. The rest were about 95psi( this was my first comp test) but gauge worked with all but cyl 1!? Ive done all the basics like plugs, coil rail, cps, swap injectors, sea foam etc. flusterated please help

belvedere

Time for a leakdown test to see why there's no compression in that cyl.

Jobxj

Ok but whats the worst case scenario price wise for a fix on this? I can barely afford the diy thing. And also im learning as i go so im sure ill have some more stupid questions lol

Nicks90xj

yeah do a leak down test. you might have a burnt valve. and 95 psi is very low did you test when engine was warm? if you have a burnt valve you have to pull the head and do a valve job. but with compression that low ur rings might be bad also. time for a rebuild or new/used engine. or mabe bent lifter.

Jobxj

The cyl 1 plug looked the same as the other plugs. No oil but a little black(carbon?)build up around the top of the thread.

Jobxj

It was driven about 2 hrs prior to the test

mdnov

Did you do your compression test on a warm engine? What did the electrode look like on #1 plug? You can also try to put a little in all of your cylinders to see if your compression goes up.

mdnov

Oops, a little oil in your cylinders.

car5car

wet compression test

Radi

Can you post a few details on how you did the test? Used a screw-in gauge? Pulled all the plugs first? Cranked each cylinder a fixed number of times or for peak reading?
How's it run? Does it run as if it were firing on 5 cylinders? It would be noticeably rough if you really had 0 PSI on #1..

tjwalker

Good questions; more detail would be helpful.

Whenever you have low oil pressure on one cylinder, I always add a tablespoon of oil to that cylinder and then run the compression test again.

If compression comes up with the addition of oil, the problem is likely the piston rings. If compression stays the same, the problem is likely in the cylinder head. It's just a quick and dirty test that gives you an additional data point.