I have a 2001 XJ Cherokee sport with a P0305 code misfire on cylinder #5. I have tried the following steps to no avail...tried seafoam, replaced spark plugs, new coil pack, tested injector #5 with noid tester. Any ideas on how to proceed would be much appreciated.

 

have done a compression check?

 

Thanks for the reply. I will try a compresion check, but the weird thing is it seems to run on all cylinders when its cold and starts misfiring when warmed up. Could this be a vaccume leak or sensor going out with this symptom?

 

Finally picked up a compression gage and the compression seems good averaging around 135. I also sprayed some starting fluid around the vaccumes and no leaks detected. Any suggestions how to proceed is appreciated.

 

you didnt say wires.....

 

no wires on a 2001 ding dong

 

haha. and that goes to show how much i know about jeeps

 

are you getting an 02 sensor code?

 

how often does it happen ... all the time or just once in a while?

 

i have also read something about "heat soak" on the newer ones. something todo with the intake manifold getting to warm. but it usually effects the 2 inner most cylinders. Try some form of heat insulation between the exhaust and intake mani. Even if it doesnt fix you problem it will help with power and mpgs

 

Sorry its been awhile but I've been broke so the jeep has been sitting in my driveway since my last post. The misfire seems worse now and is constant from the time I start it cold and progresses as it warms up so I don't think its the heat shield issue. I finally scrapped up a little money and took to my mechanic and discovered its now showing cylinder #5 & #6 and multiple engine misfire codes. He hooked up a vacuum tester and that checked out ok. He also hooked up a fuel pressure gage and was reading good fuel pressure. We tried some Heat & fuel injector cleaner with some fresh fuel in case it was a bad fuel problem but no change. The mechanic now suggests I try new injectors or a replace the computer CPU. Any suggestions of which direction to take?

 

I sort of feel your pain. I also have a 2001 and I've been getting the P0306 code when i'm really hard on the accelerator. I've had a few things done. My valves rotated, cleaned, seafoamed, spark plugs changed. I don't get it as often, but occasionally I do. I'm just taking it easy on her until I get my stroked 4.7L Stroker.

 

had the same problem back when I had a grand Cherokee it ended up being a timing issue causing the miss fire also your dist. cap and rotor are always something to check can't hurt

 

I finally took it to the dealer and they diagnosed the PCM was causing the misfires. The dealer wanted close to 1000 for a new computer so I looked on ebay and got a refurbished one flashed with updated firmware and programmed with my VIN number for 150. Poped it in and guess what, it STILL is misfiring! The dealer did put in a heat shield for free to cover the recall, but that obviously did help the misfire. Any other ideas is appreciated before I sell it for what I can get for a misfiring 2001 jeep cherokee sport. Maybe $3k.. any takers? So far I did the following:

New Plugs
New coil pack
New PCM (computer)
Heat shield
Injector noid test
Swapped injectors
Compression check (135)
Seafoam
Fuel pressure test
Oil pressure test
Hydrocarbon test
and took to a Jeep dealer for diagnosis

 

Have you changed your plugs?