'97 Rough idle, misfire problems...Next step is to sell car.
02-22-2021, 08:33 AM
#17
Junior Member
I believe that I have the same issue on my 1998 which is now at 260,xxx miles. Sometimes the idle is really smooth and then other times, it is obviously misfiring on 1 or 2 cylinders. But it is only at idle and MAYBE a hair above idle. Listening out the exhaust provides a rhythmic "pa pa pa pa pa pa" noise indicating the misfires. Sometimes they are enough to trigger misfire codes, sometimes not. Otherwise, I can drive it across the continent without issue. Gas mileage is what it should be, it makes plenty of power, etc. Oil consumption is negligible.
I still have to get off my lazy bum and hook up my oscilloscope to the cam and crank sensors to look for a problem. Also, since the misfires appear to be on cylinders #1 and #6 (coincidence that they are partners?) I am questioning the possibility of a damaged crankshaft reluctor. Spark plugs all look good and consistent, as does compression readings. I have not checked intake valves for buildup, either. It also appears as though the crankshaft sensor has been replaced at one time (before I got it) and the aftermarket units are notorious for making these things run improperly. If you search YouTube for South Main Auto (this guy is a GREAT mechanic) for when he fixed a 2000 XJ by swapping the crank sensor. It ran fine, but the check engine light would flash indicating misfires. The oscilloscope reading of the two sensor didn't show anything obviously out of the ordinary, but the installation of the sensor directly from Chrysler fixed it. In this case, it didn't run any differently, but the check engine light flashing stopped.
Another thing that I haven't seen anyone look at regarding this issue is the timing chain. Its not making any noise, but back in the day, loose chains caused rough running. In either case, a look at the cam and crankshaft waveforms should pick out an issue there.
I should also add that this thing has been doing this for over 10 years and 60,000 miles now but seems to have become worse in the last year or so.
I still have to get off my lazy bum and hook up my oscilloscope to the cam and crank sensors to look for a problem. Also, since the misfires appear to be on cylinders #1 and #6 (coincidence that they are partners?) I am questioning the possibility of a damaged crankshaft reluctor. Spark plugs all look good and consistent, as does compression readings. I have not checked intake valves for buildup, either. It also appears as though the crankshaft sensor has been replaced at one time (before I got it) and the aftermarket units are notorious for making these things run improperly. If you search YouTube for South Main Auto (this guy is a GREAT mechanic) for when he fixed a 2000 XJ by swapping the crank sensor. It ran fine, but the check engine light would flash indicating misfires. The oscilloscope reading of the two sensor didn't show anything obviously out of the ordinary, but the installation of the sensor directly from Chrysler fixed it. In this case, it didn't run any differently, but the check engine light flashing stopped.
Another thing that I haven't seen anyone look at regarding this issue is the timing chain. Its not making any noise, but back in the day, loose chains caused rough running. In either case, a look at the cam and crankshaft waveforms should pick out an issue there.
I should also add that this thing has been doing this for over 10 years and 60,000 miles now but seems to have become worse in the last year or so.
02-22-2021, 11:13 AM
#18
CF Veteran
02-22-2021, 11:36 AM
#19
CF Veteran
Join Date: Dec 2015
Location: PA
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Year: 1997
Model: Cherokee
Engine: 4.0L
02-22-2021, 11:50 AM
#20
CF Veteran
02-22-2021, 01:16 PM
#21
Junior Member
There may be some terminology discrepancies. The way I learned it is that partner cylinders are at top dead center at the same time and conversely, bottom dead center.
In either case, #6 and #1 utilize the same reluctor hole in the flywheel.
In either case, #6 and #1 utilize the same reluctor hole in the flywheel.
07-07-2021, 09:09 AM
#22
Same issue for my 2000 XJ
Howdy fellas,
Owned my Cherokee for a year. It developed a rough idle/misfire issue after I bought it and have really fought it. Two shops looked at it and told me it was ok -- it's not.
I'm at my wits end with it and probably going to sell the car if I can't fix it here in the next month or so.
The car idles rough. It shakes around noticeably at idle. It's not bucking or anything but as my dad put it 'feels like it needs to clear it's throat.' It will occasionally throw a cylinder 1 misfire code that goes back away in time. If you idle it for a while, especially after running it hard, it will SOMETIMES break into a more violent rough idle that throws cyl 1,3, and random misfire codes. When it does this the throttle appears to really struggle and it appears to want to die. After running for a bit again it clears it up.
I have replaced:
Plugs, cap, wires, rotor, fuel pump, IAC valve, upstream O2, added heat shield to injectors, and TPS.
I have:
Checked compression (150 +- a bit on all cylinders)
Checked oil pressure (a bit low at hot idle, around 11-13, normal when driving)
Block checker (for head gasket leak) got normal results
Vacuum check (low (15ish) but appeared to function normally)
Checked fuel injectors (nothing leaking, normal resistance on all, can hear all firing with stethoscope)
Checked fuel pressure (49)
Checked for excessive buildup with scope in cylinders
Seafoamed throttle body and fuel
Oil change
Cleaned air filter
Checked for vacuum leaks with carb cleaner and visual inspection of lines
Cleaned grounds
Tried higher octane fuel
The things I have noticed: It has burned a slight amount of coolant while I've owned it, not a lot, just enough that I have had to top off the reservoir a couple of times. The AC has stopped working (compressor works, recharged it with dye, didn't see any leaks, so not sure). The exhaust system looks a bit rough, cat appear to have been welded in/replaced at some point, and the exhaust smells bad.
I've read every thread on this board and others about this and haven't gotten anywhere. Besides shooting parts cannon I have no ideas.
Thanks
Owned my Cherokee for a year. It developed a rough idle/misfire issue after I bought it and have really fought it. Two shops looked at it and told me it was ok -- it's not.
I'm at my wits end with it and probably going to sell the car if I can't fix it here in the next month or so.
The car idles rough. It shakes around noticeably at idle. It's not bucking or anything but as my dad put it 'feels like it needs to clear it's throat.' It will occasionally throw a cylinder 1 misfire code that goes back away in time. If you idle it for a while, especially after running it hard, it will SOMETIMES break into a more violent rough idle that throws cyl 1,3, and random misfire codes. When it does this the throttle appears to really struggle and it appears to want to die. After running for a bit again it clears it up.
I have replaced:
Plugs, cap, wires, rotor, fuel pump, IAC valve, upstream O2, added heat shield to injectors, and TPS.
I have:
Checked compression (150 +- a bit on all cylinders)
Checked oil pressure (a bit low at hot idle, around 11-13, normal when driving)
Block checker (for head gasket leak) got normal results
Vacuum check (low (15ish) but appeared to function normally)
Checked fuel injectors (nothing leaking, normal resistance on all, can hear all firing with stethoscope)
Checked fuel pressure (49)
Checked for excessive buildup with scope in cylinders
Seafoamed throttle body and fuel
Oil change
Cleaned air filter
Checked for vacuum leaks with carb cleaner and visual inspection of lines
Cleaned grounds
Tried higher octane fuel
The things I have noticed: It has burned a slight amount of coolant while I've owned it, not a lot, just enough that I have had to top off the reservoir a couple of times. The AC has stopped working (compressor works, recharged it with dye, didn't see any leaks, so not sure). The exhaust system looks a bit rough, cat appear to have been welded in/replaced at some point, and the exhaust smells bad.
I've read every thread on this board and others about this and haven't gotten anywhere. Besides shooting parts cannon I have no ideas.
Thanks
can we get an update on what your learned? Same exact symptoms for my 2000 XJ
07-07-2021, 09:32 AM
#23
Junior Member
It would explain why my 4.0 does the same thing, yet compression is what a person would expect and the misfires aren't consistent. It has been doing it for the last 60,000+ miles.
You may want to do a relative compression test, but that requires equipment to do it. Go ***** out with it, stop and notice how it is running poor, and immediately do the relative compression test.
I got done doing something similar with an old Ford Ranger with the Vulcan V6. I sent the heads in to get rebuilt and it runs mint now and the customer is happy. Sometimes you couldn't really tell there was anything wrong, and other times it would idle rough. It was worst after giving it the beans and running it hard as described here.
After all, all the keyboard warriors changed every single related part to no avail except for getting a valve job done. Throw more parts at it or do some testing or have the head rebuilt.
Last edited by Paul Standaert; 07-07-2021 at 09:35 AM.
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