Turbo X_J

We are both talking about bringing a cylinder to TDC, using compressed air, then a differential gauge to determine leak down, right?
If the leak is:
past the rings you can hear air escaping out through the oil fill,
past the intake valve, through the intake manifold,
past an exhaust valve, through the tail pipe, etc.

Whereas "fast leakdown" of a compression gauge, sounds like a bad gauge assembly.

superbyrd

as stated earlier, already pulled compression and leak-down tested all cylinders, i don't have a cracked head or any head gasket issues.......

macgyver35

Since it seems you have already replaced half the sensors, etc. and con formed that you don't have an exhaust blockage, I'm leaning toward a couple of things:

1) Have you replaced the CPS with an original Mopar unit? I don't recall seeing that in the thread, but I may have missed it.

2) Since changing none of the electrical thingamabobs has given an improvement, couldn't it be a wiring issue related to the ignition system or one of the Hall sensors (crankshaft position sensor / camshaft position sensor)? Have you checked for short, melted wires, corrosion, etc?

My '02 Wrangler had a failing camshaft position sensor and it had similar symptoms to what you describe.

Also, I've seen it fairly common where a failing CPS (Crankshaft) will cause a 4.0 to idle like crap, but give it some throttle and it will smooth out.

XJ4LIFE52

Had the same issue with my 2001 xj. Mine had really hard starting though. Kept throwing parts at it with no result (same thing your doing). Compression good, exhaust flowing properly, etc. Finally took it to a 4.0 specialty shop here in Atlanta & turned out the electronic timing was way off. They re-flashed my ECU and all was good. Also checked the fuel system pressure while off and running and installed new injectors.

ckysodkorn_xj

not quiet sure on the whole reflashing thing, never seen anyone do it.. but i would definatly hook it to an engine scope or a good diag computer like a snapon modis or something and look at things while its running. will let you find out whats no communicating with the computer, or you may possible find that the computer's not commuicating with the parts.. wich is what im leaning twards. so in english i think its your ECU fuel map could be off or anything of that nature. try it and see, if it doesnt work you can all ways take it back.

superbyrd

well, tried the old trick of spraying stating fluid around where the intake manifold/exhaust bolts to the head,........found an intake/vacuum leak. #6 cylinder. when i spray the ether at the intake, it actually bogs the engine and tries to kill it, with a hard dieseling sound. still throwing the PO301 code, cylinder 1 misfire, so, i will replace the intake/exhaust gasket and go from there.....