Intermiitent Problem P1391 (and now P0340) - Jeep Wrangler Forum
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Old 03-04-2013, 05:52 PM   #1
Join Date: Dec 2012
Posts: 2
Intermiitent Problem P1391 (and now P0340)

Back in November I bought a 99 Wrangler 6cyl Auto and it was running great. Going from Albany and Syracuse a few times just fine. Sometimes though if it was cold the engine would act a little weird and run erratically; the tachometer would jump by itself without me doing anything. but if I let it sit and warm up it'd work it self out.

Fast forward to mid December when I'm heading back home to Albany from Syracuse when shit hits the fan. The engine revs erratically, it backfires and letting it warm up and restarting the engine does nothing. I manage to get it home and after an hour of the engine running bad like that the CEL comes on.

I didn't have the time to work on it myself so I drop it off at my local garage. They tell me it's problem code P1391 which comes up as a Camshaft Sensor problem. They go ahead and fix it, but a couple days after that it all happens again. They say it could also be the Crankshaft Sensor so I have them replace that too. This time it only lasts till the next day. They say they're not sure at this point, but it could be the ECM and they quote me $2000 to replace it. I bring the car home and replace it myself for $300. Runs fine at first then once I rev the engine to about 3000 it all goes back to the same with the same trouble code.

I bring it back to the garage and tell them to do what they have to and just find out what is wrong and fix it. Around that time I had to go back to school so I left it there for them to work on. They do diagnostics and call specialists and such. They end up finding a broken line in the wiring and patching it doesn't work so I buy a used engine wiring harness online and send it to them. They replace it and all the problems go away! My parents drive it for a couple days to test it then bring it to me in Syracuse. It runs fine for 2 weeks there and then I go home for a visit and it makes it fine.

Then once again shit hits the fan and on my way back to Syracuse it all happens again, the back firing and the erratic revving. I get it to stop doing it a few times by stopping the car, but it comes back after a few minutes of driving(even if I kept the rpms low, no higher than 2300). I manage to get it back to Syracuse and I find 2 trouble codes this time P0340 and P1391.

Any ideas?

Symptoms: Engine revving erratically-intermittent
Engine Backfiring-intermittent
Happens when it's cold out more, but not exclusively then
Codes: P0340 and P1391

Already done: Crankshaft Sensor replaced-new part
Camshaft Sensor replaced-new part
Engine wiring harness replaced-used part
ECM replaced-refurb part

I will happily answer any questions you guys have. I'm just getting very very frustrated with this. Thanks for any help you can give.

kbibs31 is offline   Quote Quick Reply
Old 10-09-2013, 07:49 AM   #2
Join Date: Sep 2013
Posts: 6
any luck?

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Old 10-09-2013, 07:50 AM   #3
Join Date: Sep 2013
Posts: 6
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Old 10-09-2013, 08:18 AM   #4
Fitzey5435's Avatar
Join Date: Mar 2012
Location: Southern Ontario
Posts: 142
I went through the exact same thing you are experiencing. I changed both crank and camshaft sensors. I eventually got a used ecm off of eBay and the problem went away. I'll try to keep this short, but before all of this happened I replaced the plugs in my jeep and I didn't gap them properly which ultimately messed up my spark and threw off my ecm's brain as far as fuel is concerned. What I am trying to say is that to this day don't think the problem was the ecm.... it was improperly gapped plugs. One more thing..... if you replaced those sensors with crappy aftermarket sensors that will not help your situation either.
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Old 10-11-2013, 07:30 AM   #5
Join Date: Sep 2013
Posts: 6
did you get the P1391 code also?
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Old 10-11-2013, 08:21 PM   #6
Fitzey5435's Avatar
Join Date: Mar 2012
Location: Southern Ontario
Posts: 142
Yes I did have 1391. Remove the crankshaft sensor from the bell housing and make sure it's clean and free of grease/grime. I replaced mine with a crap one from eBay and it ran worse. I then pulled my old crank sensor off the shelf, cleaned it up really good and reinstalled the original. Worked great. Check all your plugs man.

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