So, engine light came on a week ago, threw it on the scanner and it came up with 3 & 4 missfire. I figured id do plugs and coil rail. No help. did the compression test yesterday and cyl. 3&4 are only giving me 20 psi. A long way off from the 120-150 the book says it should be at. Anyway I've heard everything from check the valve springs to buy a new motor. Just a devastated jeeper Looking for solutions or guidance here guys. Thanks.

 

Did you do a leakdown test? Start there and it should help indicate where the problem lies. Do it before you take anything apart. Could be as simple as a bad head gasket if you're lucky.

 

I would do a wet and dry compression test, If you don't have a leak down gauge set.

Dry test is just in its natural state ,most likely how you already did it, pull plugs and test.
Wet test you drop 5-6 drops of oil into the cylinder ,threw spark plug holes and retest comparing to the dry test results.

If it gets better with a wet test then its a ring issue(lower end), if it stays the same its a head/head-gasket/valve issue(upper end). But with 20 psi I would guess its a head gasket or head. A leak down test is a good test tells you for sure where its coming from.

I am not one to throw this around lightly or at EVERY thread on newer XJ's, But since you mentioned a coil rail, yours is a 2000, or 2001, which has the 0331 head code. A Cylinder head that is known for cracking between cylinders 3 and 4.... If you take the oil cap off and shine a flashlight straight down into the fill hole, you could see a green line from the coolant seeping threw the crack(if its cracked). The oil will also look milky.

Depending on the miles yours currently has it may be worth getting a new motor, Or it may just need a head/head gasket and be good to go! If the oil is milky I would highly recommend a new engine, or at least a full overhaul with a new head if its cracked.

Good luck!

 

My friends truck threw the same code it was a cracked head and his was a 2000

 

I have an 01 and am currently seeking a new head as I blew a hose and before I could pull over it overheated and cracked the head. Quick tip don't just think looking through the oil fill hole will let you see the crack, if you can't see the crack that way then go ahead and pull the valve cover, takes like 10 minutes, and you'll know for sure if its cracked. BTW that head gasket repair stop leak stuff is a poor solution, sure it solved the leak in the head, but it also clogged up my heater core and has pretty well gummed up everything in my cooling system.

 

yeah addatives for "stop leak" are not a good idea. fixing the problem at hand is the only real way to fix it. but it can help to get you buy for a little while....

Definatly pull the valve cover to really check. I come across 3 with cracked heads, and all of them i could see threw the oil cap hole. But i didn't mean to make it sound as if you can't see it its not cracked, because it still can be.

 

Yep it is a 2000 and yes did the leak down and it was pretty inconclusive except for the last time we did it my buddy said he heard air out of the top end. Thanks for all the help guys.