GregB58

My son purchased a 96 xj, 4wd (country trim), 4.0, with @ 220k on it, about a month ago. So far we have had the transmission changed (not unexpected), and we have changed the cam & crank sensors (with Mopar parts), changed all the spark plugs (the old ones were almost completely gone) changed the ignition wires, distributor cab & rotor. This was all mostly maintenance since we had no idea what had been done to it historically.

The Jeep had previously just randomly stopped running but changing the cam/crank position sensors seems to have corrected that. Right now it is throwing a P0300 & 301 error code. We really cant feel any misfire and it seems to run fine. A tad rough at idle but otherwise good. The error will stay off for about a day if cleared, but will come back.

We have done an intake air leak test with carb spray (not sure if this is the best way to test) with no change in idle at all. Last evening we did compression tests on the cylinders. Results:

1 - 150 wet 185
2 - 175
3 - 150
4 - 180
5 - 175
6 - 150

We only did a wet test on #1 because we simply ran out of light. I'm definitely no expert but is the difference in the psi for #1 great enough to cause a misfire? Also, if it is, then why doesn't it throw a P0303 & P0306 since those have the same value? Ahhh ... questions from my non-mechanic brain. If the above values shouldn't cause the error then I am leaning towards a possible fouled fuel injector. We really have no idea how long this jeep was sitting and since it is now being driven I am wondering if some crud has gotten into the injector on #1. I hope to find some 703s this weekend and rebuild them but who knows if we'll find any available.

Am I missing anything here? What steps would you more experienced folks take next. I plan on doing a fuel pressure test this evening and maybe switching the injector from #1 to another cylinder and see what error code pops up.

Unfortunately my son is in kind of a time crunch since he has to get this to pass an emissions check here in GA so he can get a new tag by September 1.