Outlaw40

Hey guys, I just picked up a 2001 XJ Sport with 135,000 miles for my girlfriend and I've been having alot of issues getting it to run right. I bought it with a misfire that had not been diagnosed, the previous owner had purchaced a 2010 durango and just wanted it gone. I bought it for the right price to cover my *** in case I had to dump it or do any major motor work, but it would really suck to have to get to that point. The truck throws three codes;

PO300-Multiple Misfire
PO302-Cylinder 2 Misfire
PO305-Cylinder 5 Misfire

The symptoms are as follows;

-After a few minutes of driving the truck will begin to throw a CEL after erased. (hard code, will not go away unless cleared) At ldle and under light acceleration you can feel the misfire, and the CEL will flash. Under heavy acceleration however, the truck will buck heavily and not want to accelerate unless you back off on the throttle and accelerate moderately.

I should point out that during the first minute or two of driving the truck, you can drive it however you want, run it to redline, stop and go, rev in neuteral, etc. and it will be just fine.

I've been doing alot of reading/ research on this, as my ol' girl (1998 XJ Sport) has distributorized Ignition and different injectors, so I've never messed with the COP system on the XJ's up until now.

Started by switching out the plugs (Copper Champion plugs gapped .40)
Coil rail looks newer, but I ohm tested it, from what I read it should read 0.6-0.9 at each coil, mine read 0.9-1.0 which to me is close enough for govornment work to carry on.

I then went on to test each injector individually, and came up with anywhere from 12.8-13.7 ohms on the injectors. I had two laying around, so I went ahead and popped them in #2 and #5, and that had no effect on the problem.

The truck does not overheat, and runs between 208 and 216 according to my scanner. I drove it 90 miles home from Milwaulkee to Chicago and it did not go above 210 on the dash.

My question is... What should I look for next? I'm going to do a cylinder contribution test today, but other than that, I am out of ideas without consulting a dealer. I HATE throwing parts at problems so any more tests to be conducted would be greatly appreciated.

TIA guys

Turbo X_J

First off do a compression test. What did the old plugs look like when you changed them? (flashing CEL is really bad news btw) See below, if sparkplugs from 2-5 were fouled could be the coil pack.

ETA: From the FSM:

cylinder is being wasted (on exhaust stroke).

Outlaw40

Plugs were clean, had a good burn on them and had definitely been in awhile. Were all gapped. 35-.37. No residue on them.

I will do compression test to rule it out. The more and more I think about it, it may be crank position sensor.... #2 and #5 are on the same stroke, could be CPS or even flexplate.

Gambulski

I have been reading through numerous posts and I would like to know how these stories end.

First of all, I have a 2001 Cherokee, 6 cylinder, and it all started with a code for misfire.

Replaced the Coil-Rail...no change

Put in a new crank position sensor...no change

Added Fuel Injector cleaner....mild results...sometimes helped, hard to tell...

Have been dealing with the misfiring, which shakes the truck terribly for almost a year now and even had a good friend of mine check it out and see what he thought, with his diagnostics tools...thought it might be an injector....

I just took out all the injectors and had them checked...all were fine.

Just to be sure, swapped all the injectors around, making sure the center ones were not the problem...no change.... even pulled the plugs while running to see if it helped....hard to tell, midly affected it.

Have NOT done a compression check

But think that a compression check is going to yeild what every one else has been saying...good compression....

Is there something I am missing?

I am ready to chuck this thing!