Hey guys, I have an issue with my 2001 Cherokee XJ (210k miles). When I bought it had a slew of problems... no gauges, no oil pressure, no windows, lifted 2 inches on 33s with stock axle (don't worry it's now on 31s with a brand new 3" lift) the typical 2nd gen Cherokee issues. Once I figured out the gremlins, I plugged in my tracker which reads codes too, I got a NSS code for range (p0705), which is due to the NSS not being good -gonna replace it already have the new part. I also have the p0740 which I'm assuming is a dirty connection or involves the NSS garbage. It shifts into OD so nothings off with the transmission, fluid level is good.

Ultimately, my curiosity lies within my p0300, p0301, p0303. p0304, p0305... etc. I am pretty sure I have gotten them all -and the thing is it doesn't feel like it's misfiring at all, great idle, feels smooth in the high range (when it typically flashses at me). So far just as general maintenance and assurance since it's gonna be my daily for a good while I've thrown in new plugs (Champion Coppers), coil pack, 4 port k-suspension injectors. I have tried clearing the codes and they still persist, and once again it feels like it's nothing... Also before the dreaded 0331 head defect is mentioned, I know of it and did a compression test and they were all within spec (albeit on the lower end), with 125 being my lowest and 135 being my highest (in fact cylinders 3 and 4 were higher than most). At this point I am wondering if possibly my ECU is funky, or maybe my transmission problem could be causing the codes/misfire.

I am posting it here in the stock non-modified because the problem has persisted since before I installed the aftermarket 4 port injectors.

Any ideas? It's just really strange because if it was misfiring on all cylinders I am quite certain I would feel it...

 

Have always had intermittent misfire codes on my 01. Never really felt anything...changed out my coil rail with a coil pack. Seemed to get better but as still intermittent and widely spaced apart. Then put in a high voltage coil pack. Ran better but one day started getting cyl 2 misfire and the jeep was shaking bad. Turn off and on and sometimes cleared up sometimes not but when it was shaking real bad and i gave it gas..the cel would flash.. gave a turn on the spark plug wire on the coil and it all cleared up. Rumor has it that the O2 sensors are used for misfire detection...cant confirm that. O2 sensors are cheap enough..change out the bank 1 /1 and 2/1. See what happens

 

Yeah I feel like it is likely sensor related because it runs like a top, no hesitation or anything. I will definitely consider swapping the 02 sensors. Thanks for the suggestion!

 

That's a new one. Can't imagine how that would work.

Compression test won't show the common 200/2001 head crack, which lets coolant weep into the valve cover area.

 

An erratic crank sensor, perhaps.

 

They also had issues with carbon on the intake valves not allowing the valve to seat like it should.

If it were mine, I would buy some BG 44K and use the can like this:

Add to a full fuel tank.
Drive til it gets down to half tank and fill with gas.
Drive til quarter tank or less and refill with gas.

 

I had been battling these same codes for the last 18 months.
2001 4.0l XJ.
I tried Cruiser's idea, although I couldn't find BG 44k, so tried Lucas "Complete Engine".
This did seem to clear up the issue for about 9 months, then the codes started up again.
Just like yours, I couldn't feel any misfires. The Jeep ran well, etc, etc.
Recently, it got to the point where I couldn't drive the Jeep at all without getting the codes.
I would clear them and they would pop back up within a few miles.
I replaced the coil rail with an MSD, replaced the Cam sensor, installed re-man Bosch 4-port injectors
and removed the throttle body for cleaning.
It was jet black inside and the throttle body cleaner I was using barely made a dent in it.
Required scrubbing with a brush, and some light scotchbrite.
(Also replaced the IAC, because it was black as well.)
I'm not sure which of these things was the reason for the misfires, but they are gone.
Jeep does feel noticeably smoother.
It would have been nice if I had the opportunity to make all of these changes one at a time, so that I could be sure of what fixed the problem,
but time didn't allow that, and I'm just glad they have stopped.
Good luck!

 

I have a horseshoe intake, 4-hole injectors being ordered as soon as I can find some 703's, and then a new exhaust header, pipe, and muffler. All this to get the power back that I lost by putting on tires and a 4.5" lift.
I'm going to clean the sensors and everything else that can effect a smooth running engine. Replace the PCV and CCV valves because they barely make a rattle sound anymore. I don't have any codes that are causing a CEL right now, but my jeep does have a very slight rough idle and I haven't tracked it down. Already have new plugs, wires, cap, and rotor. Haven't done a vacuum leak test yet though.

So I'm not sure if I have a weak spark in a cylinder, vac leak, or another sensor that's dirtied up...

 

There is no knock sensor on later jeeps...I asked same question when I had my misfires codes...they said they know what cyl is firing from either the crank pos sensor or the cam sensor and then if the associated o2 sensors sees a bad combustion cylce, It registers a misfire associated with the last firing pulse...I can kind of see it...dont know if its accurate. It would depend upon the consistency of the speed of the exhaust gas cycle from the cyl to past the sensor...but the 2000 and 2001 all seem to throw a lot of misfire codes when apparently running well

 

Nothing compares to BG 44K!!

 

First, check the intake manifold bolts. Likely loose a bit. Tighten them in this pattern. Best done with air cleaner box removed. Forget any torque specs. Get em tight.

 

Thanks for all of the advice! I will try and track down some BG 44K and use it as Cruiser suggested. I am also going to go ahead and clean my throttle body, that sounds like a good idea anyways and I was considering replacing the IAC as well. I will try the above methods and I will report back on if any of them work! Thanks again!

 

Hey guys, I have an update, I ran BG44K and unfortunately I still get that missfire code at around 3k RPM. It seems to happen mostly on the highway now, but the thing is, is it still runs great with the codes. It's really strange. I think my next step from here is going to be cleaning my throttle and intake and seeing what happens from there. I have since bought a second jeep to daily while I work on my XJ so I should have a lot more capability here in the near future!

 

Wanna try one more thing first? https://www.cherokeeforum.com/f30/st...-4-0-a-226299/