Well long of the short I got a 2001 xj (sold my 95) and the vehicle needed a head gasket. The Jeep would start and idle smooth , just the temp gauge would go up and the orginal owner said he had low compression in two adjacent cylinders. So what I had done

-Head Was checked, resurfaced and valve job with new seals

-New plugs , changed oil/ and coolant

So going to start it up the vehicle would not start, but crank. Found out the battery only had 11.7 volts so I changed that out and boom, Jeep started.

Have a miss in cylinder 1 and 5. Had fuel/spark so I checked compression. 60 psi in both, the rest are at 140ish.. Added oil to the cylinder and they shot up to 180. Put plugs back in and started up and enjoyed the smoke show. Vehicle started to idle like crap again. At a loss as to what it could be? Thing idled perfect before I took it apart, currently took it up to my work to have the leak down test done tomorrow to make sure its not a valve (doubt it is with the oil/compression going up).

Any ideas? I don't see how I could of toasted pistons rings just changing the gasket out. Should I have let the oil sit longer to help a stuck ring? Any advice would be awesome. When driving the vehicle drives smooth and has No CEL for a misfire.

with the psi going up with oil that would be the rings for sure. is it 4x4?
u should be able to take the oil pan off and pull the rings from the top.
it would be easier with 2wd but could be done with 4wd.
u buy rings in a full set so just do them all and make sure to hone the cylinders (deglaze) before putting in the pistons with the new rings.run for 500 miles then change the oil. make sure not to sure full synthetic and no better then a blend.

Hmmmm. 2001 model with an 0331 head?

Probably should have replaced the head outright with an aftermarket new one.

Any coolant loss yet?

None that I can see/nothing burning out the tail either. I was going to get a new head but when the machine shop stated no cracks I did not question it.Hell he was amazed it wasn't

As far as the rings I put more than a tsp of oil in which I read can fluxuate the numbers. Just confused how the car was fine then the rings are toast within a day? Could two get stuck that quick? If the leak down test does verify rings then I thought about trying the Marvel Mystery Oil in the cylinder over night to free up the rings.

did you verify that the original owner was right, and checked the compression on the engine before you removed the head and sent it out? Which two "adjacent" cylinders did he say were low?

And, just because it's a 2001 , that doesn't mean that it has the 0331 head on it, may have been replaced already.

it doesnt matter how much or little oil u put in. if the readings change, especially that much then your rings are bad.

On a 4.0 with 126k? I'm just curious if I knocked some debris down in the rings. I guess I'll see once we get the leak down. When I first put a oz in the compression only went up 10lbs, added more as I thought maybe I did not add enough. I know that little could be valves, but we will see.

Just figured Ibwould post to see if anyone else had this happen to them. Thing idled/ran beautifully before it was apart.

That's what I was wondering. It's a strange situation, indeed. Keep us posted!

my 99 im working on right now
had these readings before:
#1 = 35
#2 = 30
#3 = 35
#4 = 68
#5 = 135
#6 = 160

and it ran like a top .
i had no idea that a motor could run so well with that bad psi but it did.
my prob was the head had a huge crack from the old owner.
when i put oil in it only went up very little so i knew it wasnt the rings

That's nuts. Thought a engine had to have about 80 psi to combust. I'm leaning towards something on the valve job as that was the only major change, and with the first tbsp of oil it hardly went up, jumped huge when I added a few more which from my understanding can mislead numbers. Leak down gets done Tuesday

will u do the valves your self?
they are easy but tidies.
if u need a valve spring compressor
i have a cheap way that i made one that works great.

Either the gauge is faulty or you have one of those XJs with supernatural powers running like a top. But seriously, with compression numbers like those I would at least expect noticeably lower torque.

****UPDATE****

Well finally got the time at work to due the leak down test.

Cylinder one with 100 psi had 20 psi at max at TDC with valve train on, air coming out the tail pipe

WITH the valve train removed - No change in pressure or air out the exhaust, we stopped there and did not go to cylinder 5.

Waiting for the Machine Shop to see about a refund so I can get a new loaded head through work for 315. Keep you updated

Update

Got the new cylinder head. Had 150 compression all the way across the board. Idled perfectly for 45 mins. Took her down the road and after about a mile and half I heard a pop. Car started to chug, temp gauge went up and oil pressure went down. Figured my luck threw a rod. Get out and see no damage.

Drove her home and have 0 compression in cylinder 3, all the others have 150. Took valve cover off and watched the rockers move up and down, no bent rods. Added oil to the cylinder and it made no difference in compression. Soooo now I am at a loss. Taking head back off tonight to see if there is lower end damage. If so I just plan on buying a stroker 4.6 kit from Titan and rebuilding her.

Any chance that the headgasket may have been faulty and blew causing 0 compression? No coolant in cylinder, no oil in coolant vice versa. No smoke coming out tail pipe.

Sound like a valve issue. Check to make sure one of the springs broke. If not, then I am afraid the head will have to come back off to diagnose.