"New" cherokee stalling, running rough, dont know what else to do - JeepForum.com
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post #1 of 12 Old 11-19-2008, 03:59 PM Thread Starter
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1998 XJ Cherokee 
Join Date: Aug 2007
Location: Springfield (Just South of Philly)
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"New" cherokee stalling, running rough, dont know what else to do

well i just picked up a 1998 cherokee, great condition just doesn't run right, and i got a steal on it, so i had to get it. well heres the issue:

Usually starts fine, (about 1 sec of cranking) rpms quickly rise to 2000 then settle down to 1000. seems normal so far.

then rpms will drop a little more, prob to like 800, then the problems start. it goes back and forth from about 800 to 600. it will hold at 800, then every couple seconds its like it looses ignition or something and quickly falls to about 600. then it usually saves itself from stalling and goes back up. this just repeats for a while until it eventually stalls out.

if you try to drive it, usually you can drive away ok, but once you get to the first stop sign it will do something similar to its idle, only this time it almost always stalls, but usually i can get it started again in about 10 seconds of cranking.

CEL is on, codes are p1391 and p0320. tried erasing them and they comeback immediately upon next start. both of them refer to the crank position sensor. so i went ahead and replaced that. it made absolutely no difference. i also checked its wiring the best i could and saw no problems.

i then replaced the throttle position sensor. out of speculation and ive heard stories about them going bad and not throwing codes, but this to made zero difference.

heat also appears to play a factor. it appears that as the engine gets hotter, the faster it stalls, and its much harder to restart.

if anyone has even a hunch, please let me know

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post #2 of 12 Old 11-19-2008, 04:47 PM
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Did you adjust the TPS after you installed it?

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post #3 of 12 Old 11-19-2008, 05:01 PM Thread Starter
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1998 XJ Cherokee 
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i didnt know that was required, i thought only the older ones needed it.
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post #4 of 12 Old 11-19-2008, 05:59 PM
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Sometimes the fuel injectors can heat up and cause misfires, that will throw out an error code. Not sure if that's what's goin on here, but you mentioned the temperature...

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Last edited by SB6114; 11-19-2008 at 06:28 PM.
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post #5 of 12 Old 11-19-2008, 06:30 PM Thread Starter
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1998 XJ Cherokee 
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Location: Springfield (Just South of Philly)
Posts: 16
yea idle is the worst, but that not it, you can feel something isnt right even at higher rpms sometimes. like if you trying to drive it, all of a sudden youll loose power, then it comes right back, or it will just stall out, even at speed.
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post #6 of 12 Old 11-19-2008, 07:06 PM
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1988 XJ Cherokee 
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Originally Posted by Shane01638 View Post
Did you adjust the TPS after you installed it?
Only 87-90 Cherokee's require a TPS adjustment.
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post #7 of 12 Old 11-19-2008, 07:17 PM
It's the crank sensor!
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1999 XJ Cherokee 
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Location: Central Minnesota
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The TPS on the 98 is not adjustable.

I think there is a good possibility that you have two (or three) separate issues here; the hickup and the idle quality; (and possibly the hot start problem) they are not obligated to be related.

The one code you listed could be related to either the crank sensor or the camshaft sensor. I'd start by reseating the connector on the crank sensor harness inside the engine bay near the firewall by the #6 injector. Sometimes it's an electrical contact issue.

If no luck with that, I'd start the testing process at this point. Do you have a good manual and a meter? A must for testing. I'd test the camshaft position sensor, followed by the ignition coil. Fuel pressure testing is never a bad idea.

May as well test the coolant temp sensor while you're at it; not for the hickup but it can create some hot start type of symptoms.

For your idle quality, try removing and cleaning both the idle air control and the throttle body. Procedure included for that; easy to do.

Cleaning the IAC:

1. Remove the IAC with a torx 15 driver (2 bolts)
2. Gently wiggle out the IAC from the throttle body
3. Clean the IAC with throttle body cleaner (not carburetor cleaner ) Use cleaner, a rag and a toothbrush and or Q-Tips. Be gentle; don’t twist or pull on the pintle as it is fragile and you can damage it pretty easily
4. Also clean where the IAC seats in the throttle body with the same throttle body cleaner
5. Consider cleaning the entire throttle body itself as long as you’re at it
6. Reinstall IAC and check idle quality

Good luck and post back what you find!

99 Cherokee, 4.0 AW4, NP242
Past Jeeps: 49 Willys, 81 Scrambler, 88 Comanche
Without "data", all you have is an opinion!
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post #8 of 12 Old 11-20-2008, 11:40 PM Thread Starter
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1998 XJ Cherokee 
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well ive cleaned the iac, no luck, didnt really look too bad anyway.

i thought i was replacing the cam sensor, but i replaced the pick up coil. the black disk right under the distributer cap. but after looking in the manual, it seems theres another part, the stator, which they refer to as being know as the cam sensor, and according to their pictures it is definately another part. did i replace the wrong thing?

and the thing that confuses me the most....

after replacing what i thought to be the cam sensor, and still had no luck. code 1391 keeps on coming up immediately. i decided to try unpluging the "cam sensor wire". the engine didnt even notice. it runs exactly the same with it plugged in or not. so i thought that the wiring was bad, although when unplugged it throws a new code. something about the cam sensor circuit malfunction. so it does recognize when it is unplugged, but somehow the engine runs no different? whats that mean? what would happen in perfectly running jeep if it were unplugged?

i also rechecked and cleaned all important electrical connections. and will test fuel pressure as soon as i get a hold of a gauge. i also have a new coil im going to install soon.
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post #9 of 12 Old 11-21-2008, 10:49 AM
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Haynes or Chilton's right ? The Factory Service Manual is the only one to own.

P1391 (M) Intermittent Loss of CMP or CKP Loss of the Cam Position Sensor or Crank Position Sensor has occurred.

The CKP is the Camshaft Pickup Sensor or Coil. The round thing under the distributor.

The CPS is the Crankshaft Position Sensor on the transmission bellhousing. It may be suffering from heat related stress.

Also dirty or bad ground connections cause all sorts of weird behavior. Clean and firmly reconnect the wire ends and the ground location on the body for all the ground wire. At the battery, the engine, and at the starter or alternator.


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post #10 of 12 Old 11-21-2008, 11:14 AM
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Its no surprise that the engine will run without the cam sensor connected and that it throws a new code. The only thing that the 4.0 engine management system actually uses the cam sensor for is phasing of the fuel injection pulses. If the injectors pulse out of phase (ie, they fire when the cylinder is on the power stroke instead of the exhaust stroke) the fuel just sits there on the back of the intake valve until the intake stroke comes around. Its not optimum, costs a teeny bit of power, and raises emissions, but it works. the spark timing comes from the crank sensor, and the distributor rotor takes care of sending the spark to the correct plug (on pre-2000 models, on 2000 and 2001s, two plugs fire at the same time anyway).

I hate to say it, but its really sounding like a wiring problem on the CPS circuit. You may wind up tracing that all the way back through the harness to the engine computer, and even through the computer connector itself. It could even be an intermittent on the engine computer circuit board. Don't lose faith- this is solvable and if you got a great deal on it you'll still come out ahead even if you wind up needing a new computer.
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post #11 of 12 Old 11-23-2008, 12:06 AM Thread Starter
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well from everything i hear, my issue is most likely related to the cps still. so i went back and checked it again. like i said before, i already replaced it and it made no difference. but i got a hold of a multimeter and tried testing the cps.

first i tested the old one which was still sitting around. according to the test instructions i read, the sensor is actually good.
i hooked up the two terminals and tested resistance and it read 0.L the same thing it says when its not hooked up to anything.

i then tested the replaced one which is now installed. (was an autozone part btw) on this one it read 4.5 or somthing, i forget now, but from my understanding, this sensor is actually bad.

so im confused. the brand new sensor is testing bad, the old one tested good. but both have problems once installed.

only thing i can think of is that the autozone sensor is just bad as it came, which wouldnt surprise me coming from them. and that the old one is also bad, im assuming the test cant prove a sensor to be good, just that it is bad.

so im going to try to get to the dealer on monday morning and try to get a real one from them. unless anyone has any insight.

edit: what exactly does the crank sensor read? id assume its looking at some sort of mark on the flywheel. is there any chance there could be a problem there? like if it were dirty? because the engine did used to have a real good oil leak which could have gotten all over it.

Last edited by laxmax44; 11-23-2008 at 12:35 AM.
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post #12 of 12 Old 11-23-2008, 05:43 AM
It's the crank sensor!
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1999 XJ Cherokee 
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Location: Central Minnesota
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If you're instantly coding for a crank or cam circuit problem, you're concentrating on the right things. You have to chase that code problem FIRST on either cam/crank circuit and when you fix it, the codes will not return. At that time, re-evaluate and see how your other symptoms are, if they are still there.

The camshaft position sensor has been known as both the stator and the pickup coil. Sounds like you replaced the right thing. Did you inspect all wiring leading to and just outside of the distributor that lead to the cam sensor?

Crank circuit problems are definitely more common on the XJ. You need to confirm (via testing) that the one that is installed in your engine tests good (open; infinite resistance between B-C leads). Then very carefully inspect the wiring for the crank sensor as it has been reported more than a few times that broken/ and especially burnt wiring was to blame. The sensor is only as good as the entire circuit is and that includes every inch of wiring.

Using a meter, I would try to verify that the crank signal is making it into the engine bay by checking for confirmation of that signal AT the crank sensor connector on the firewall near the #6 injector. That is another often overlooked area where the signal is lost due to corrosion in that connector and poor electrical contact. Unplug and carefully clean that connector with contact cleaner. If there is problem at that connector, your crank signal is not going to make it into the computer.

Good luck; stay on it. All of us have had gremlins like this that can be tough to isolate. Think about how happy you'll be when you finally find it!

99 Cherokee, 4.0 AW4, NP242
Past Jeeps: 49 Willys, 81 Scrambler, 88 Comanche
Without "data", all you have is an opinion!
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