Hey everyone, I need a little help diagnosing a problem before I bite the bullet and take it into the dealership. About a month ago my 2001 Jeep Wrangler Sport started hesitating intermittently. It would "hiccup" if you will about 3-5 times on an hour drive but wouldnt do it every time. This only happened when it rained oddly enough. After about a week, I finally got a CEL. Trouble code came back as P1391, Intermittient CKP/CMP signal loss. I replaced the CMP first and the problem came back the next time it rained. Next I replaced the CKP and now I have the problem all the time whether its raining or not. These were both replaced with factory MOPAR sensors and I did not see any issues with wiring to each sensor when replacing. I am seriously at a loss. Does anybody have a suggestion? Thanks in advance!
P1391: Loss of power and bucking
- Thread starter jdub89
- Start date
Get some contact cleaner and clean out all your electrical connections to CKP/CMP,,, cheapest first step. Follow your wiring harnesses and make sure you don't have any shorts where the wires are rubbing on anything. If that does not fix your problem and you have already changed both CKP/CMP, then it's probably time to change your timing set, timing chain is probably stretched. How many miles on this engine?
On the older jeeps 99 and back that still have the distributor, it is easy to check for a stretched timing chain. Pull spark plugs to make for easy engine rotation by using a socket on crankshaft bolt. rotate engine clockwise till timing mark (on crank pulley) is at bottom of degree marks (on timing cover). Pull distributor cap. Watch rotor as you turn crankshaft counter-clockwise till you see rotor just start to move (go slow). Check degree mark, if you get a reading over 10-15 degrees, your timing chain and gears need replaced. Problem is you have a coil pack, so this won't work for your jeep. Only way is to pull the timing chain cover and do the same procedure just looking at the cam gear instead of distributor rotor.
If you have done all this work, your going to change the timing set anyway, (got it apart, change it) but always do the check first. This will at the least give you an indication of whether or not the code might come back.
On the older jeeps 99 and back that still have the distributor, it is easy to check for a stretched timing chain. Pull spark plugs to make for easy engine rotation by using a socket on crankshaft bolt. rotate engine clockwise till timing mark (on crank pulley) is at bottom of degree marks (on timing cover). Pull distributor cap. Watch rotor as you turn crankshaft counter-clockwise till you see rotor just start to move (go slow). Check degree mark, if you get a reading over 10-15 degrees, your timing chain and gears need replaced. Problem is you have a coil pack, so this won't work for your jeep. Only way is to pull the timing chain cover and do the same procedure just looking at the cam gear instead of distributor rotor.
If you have done all this work, your going to change the timing set anyway, (got it apart, change it) but always do the check first. This will at the least give you an indication of whether or not the code might come back.
Update:
I chased this problem for awhile and finally took it to the dealership for diagnosis. They determined the issue was a bad PCM. I sent the PCM off to be rebuilt (no new PCMs available) and they determined hardware to be good but it had a software failure. Software was reflashed and PCM sent back. I reinstalled and no more issues! At least for a month and a half....
One day the Jeep started hesitating and bucking again out of the blue. No idea what is going on at this point. Any suggestions of where to look next? Also have codes P1391(again), and P0300. Research shows P0300 is a random misfire. Is it possible my PCM just isn't salvageable? I'm open to advice! Thanks!
Jeffery
I chased this problem for awhile and finally took it to the dealership for diagnosis. They determined the issue was a bad PCM. I sent the PCM off to be rebuilt (no new PCMs available) and they determined hardware to be good but it had a software failure. Software was reflashed and PCM sent back. I reinstalled and no more issues! At least for a month and a half....
One day the Jeep started hesitating and bucking again out of the blue. No idea what is going on at this point. Any suggestions of where to look next? Also have codes P1391(again), and P0300. Research shows P0300 is a random misfire. Is it possible my PCM just isn't salvageable? I'm open to advice! Thanks!
Jeffery
When my pcm went bad, it was throwing incorrect codes all day everyday. Once there is a suspicioun of a bad pcm, don't start chasing your tail. That is additional evidence that the pcm is likely bad. In my case, I was able to pinpoint it to 2 bad injector drivers using a continuity tester and multimeter.