Finally was able to work on it again this weekend.

Found that the yoke on the rear dif had stretched out. New driveshaft ujoint was flopping all around on it. Replaced that and solved that problem. Main vibration is still there and i'm convinced its from the engine. It has new motor mounts and transmission mount. The engine finally threw a code as well. Cylinder misfire on #4. Pulled the plugs and they were pretty corroded. Swapped plugs but the vibration is the same.

It threw the same code later that day. The distributor has a new cap and rotor but the unit is from 1999. I replaced that and it helped the idle smooth out some and seemed to pick up power. No more code. It still has the vibration. I'm determined to find this damn thing!!!

 

Edit: 1999 my bad.
Late in the game to ask, but, what year is your XJ?? I see your PCM calls out cylinder misfire, but that you have a distributor? so it isn't a coil pack. ..
So, did the 99s come with distributors, or coil packs?

 

99s had distributors. coils came in 2000. It's actually a 2001 engine in a 99. I had to pull the cam sensor and put a distributor back in

I found more stuff yesterday. The rear "PCV" hose that goes to the intake manifold was leaking and making a squeal. I fixed that and the squeal is gone. I did notice that after a day of driving with the new distributor the power is back. It's like I added a supercharger haha. Good to have it back to 100% power.

The vibration is not as bad now that the engine runs decent. Still idles a little rough, but better. I'm getting closer! I'm about to stick a gopro under there and drive around...

 

So, how does the pcm in your 2001 sense that there is a misfire and set the code you mentioned when there isnt any coil packs on the 99 engine?

"The engine finally threw a code as well. Cylinder misfire on #4. Pulled the plugs and they were pretty corroded. Swapped plugs but the vibration is the same."

 

PCM is from the 99. All the wiring is a 99. I just yanked the cam sensor and installed the distributor from the 99 and away i went. The cam sensor in the 01 is identical to the distributor, it just has a sensor on top instead of a rotor and cap.

 

I found the answer myself. On my 97 when I disconnected an injector while running, it sets that code as well, despite having a distributor. So I would pose that your code is from an open circuit to, or within, an injector. Time to break out the ohm meter and check resistances of injectors. After that, check each pinout from the pcm to the injectors, assuming they all have B+ to the other side. This is where a multi trace oscilloscope would come in really handy. You could check the pcm outputs for the injectors, something I would like right now to be able to do with mine.

 

Replacing my distributor stopped that code from popping. And i got a lot of power back that i had lost. Pretty sure that distributor was on its last leg.

 

Since you say you still have a “rough idle” and we know of the previous cylinder 4 code . I’d also be checking out cylinder 4 fuel injector wiring and compression checking it .

 

Add to that cylinder leak down , and cylinder balance test (compare rpm drops when unplugging injectors, look for one that doesn't drop much) These won't solve the problem but will point you in the right direction.