Hi folks, I just recently bought a 99 2 door sport, 172K, and the 4.0L is giving me fits. I've given it a complete tune up, new ignition coil, fogged it with seafoam, injector cleaners, and it is still acting funny. I'm replacing the TPS tonight, but I don't really expect that to fix it. At idle the entire jeep shudders (it's worse in gear), check engine light is on. I had it scanned, intermittent misfire on cylinders 1 and 2. Fuel injector was unplugged, slight change. Plugs are firing. So we did a compression test and cylinder 2 (the only one we tested), is showing around 80 PSI. Sad face.


So now, my question is, what are my most likely culprits? I know it could have a valve not sealing, or possibly a broken valve spring. The oil and water are both steady and not contaminated, so I think the head is ok. It had a new head installed shortly before I bought it (the original one overheated and cracked). I'm hoping the head gasket wasn't torqued in sequence, and that could cause my low compression? I probably need to compression test the other cylinders. How do I know that it isn't a stuck/broken piston ring? It runs great above 1500 rpm.


Does anyone have any advice? What should my next course of action be?

 

Toss a tablespoon of engine oil in the sparkplug hole and check it again. If compression comes up substantially it's probably a ring issue.
Then check the other 5 for comparison.
Do you see any gas bubbles in the radiator if you run it with the cap off?

 

UPDATE. Cylinders 1 and 2 are both under 80 PSI. The remaining cylinders are 120, 120, 120, 135. The oil test did not change the readings. A leakdown test is suggesting the intake valves may not be sealing.


The head is off, the head itself looks new, block and pistons all look fine, the head gasket was fine. BUT, we did the ol' pour diesel fuel in the valve runners on the head trick, and bingo, the front 2 intake valves are weeping pretty bad. Going to try hand-lapping them tonight, hopefully that will seal them up.