joemomma22

Hey everyone. A buddy of mine just picked up a '99 xj 4.0 aw4 with 200k miles. he bought it with a misfire on cylinders 2 and 3. He's done a full tuneup (plugs, wires, rotor cap, oil coolant etc), new headgasket and it was still misfiring. he took it back apart, had the head planed (the machinist said it was warped really bad between 2 and 3 and required a couple passes to correct). new gaskets (again) slapped it back together and bam! still misfiring. but very rarely and no where near as bad/violent. still though it does continue to misfire every now and again especially while cold.

It's worth mentioning that prior to milling the head, plugs 2 and 3 were a little oily, and after cleaning and milling the head the plugs no longer get any oil on them.

Cylinder 2 (while hot) is currently only getting 60 lbs on a compression test.he thinks he might have a stuck lifter or something but he has no clue.

Any suggestions? At this point we're considering changing the block but obviously we'd like to avoid that if at all possible.

skife

If cylinder 2 has 60lbs of compressuin, there is your problem. When the head was off, did a valve job happen to be done? If not, with the engine running, unhook the pcv from the air box, does it seem to have quite a big of air coming from the pcv?

joemomma22

yes I am aware that that was the issue I just wanted to give the backround as to how we got there so someone didnt say do headgasket or mill the head or some crap....

i dont think the valves have been touched at all. currently the truck is put together and running, intermittently missing... its very random now not consistent.

Also there is no check engine light for the misfire anymore even after running for upwards of an hour. the only code that the reader pulls from the ecm is P0138 which is for the 02 sensor circuit.

joemomma22

He says it is sucking, not blowing.

s346k

leakdown test will tell you exactly where it’s losing compression.

joemomma22

After a wet/dry compression test, cylinders 2 and 3 fail on both... so its valves right?

Waynerd

A leakdown will tell you where the leak is as s346k stated. Just listen for the air. In exhaust would be exhaust valve, through throttle body would be intake valve and through the dipstick tube or valve cover would be piston rings. Also when pulling the head the first time for any reason it would be good practice to lap the valves or at least inspect them closely. It's totally worth a little extra time and effort especially if the head is already off.

tech

Did he have the valves check when the head was off ? or it could be the valve springs are weak . just a couple more things to look at .