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Unread 08-01-2009, 02:09 PM   #1
nousernamesleft
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P1391 after replacing crank position sensor

Hey guys (n gals)..new member here with a problem. I'm trying to fix a friends 2001 cherokee classic. He was having cylinder misfires and multiple cylinder misfires, occasionally the car would shake badly on idle. a new coil pack was fitted, new plugs, oil change, new idle sensor.
He just got back from a 200 mile drive and complained that when he got there the a/c wasn't working (blowing warm air i think) the car was very lumpy at idle, and when it stalled would not restart until 1 hour later. i checked the OBD and it had a multiple cylinder misfire code and cylinder 1 & 3 misfire codes.
I just got replaced (20 mins ago) the crank position sensor and now there is a P1391 code and it feels like the engine is misfiring or something, when it had misfire codes before the engine idled very nicely ( except for the few lumpy occasions)..I don't get it...any idea what could be going on.

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Unread 08-01-2009, 02:48 PM   #2
CJ7-Tim
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What is an idle sensor ? Do you mean the Idle Air Controller, sometimes called an idle stepper motor ?

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

Where did you buy the Crank Position Sensor ? Is it installed correctly ?

Reboot the ECU/PCM engine computer using the instructions below.

This very simple procedure will Erase the “Adaptive Memory” stored inside the PCM and allow a new “Adaptive Memory” to be developed.

After performing this procedure the PCM will re-learn and store into Adaptive Memory your engines performance characteristics.

Please perform these steps exactly as they are written, in the order they are written. This will cause the adaptive memory in the PCM to be erased and cause the PCM to go into Fast Learn Mode adaptive mode.

Disconnect the POSITIVE battery Terminal and touch it to ground ( not the battery negative terminal ) for 30 seconds. The engine block or the A/C compressor pump will work as a ground. (This is to discharge the PCM capacitors, which maintain the Adaptive Memory.

Reconnect the Battery Cable
Turn Ignition Switch to the “On” position but DO NOT start the engine
Turn Headlight “On”
Turn Headlights “Off”
Turn Ignition Key “Off”


The PCM Adaptive memory has now been flashed, or erased from the PCM.

When you start the engine it will be running off a set of pre-programmed tables that come with the PCM from the factory.

When you get the engine up to operating temperature the PCM will start to collect data for the “Adaptive Memory”.

The PCM will collect data for Adaptive Memory for the first 50 Warm-up Cycles.
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Unread 08-01-2009, 04:29 PM   #3
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yes i did mean the idle air controller.
Crankshaft position sensor bought new on ebay..yes, installed correctly.

I just asked my bud about the "new" misfire, and he said it was doing that on his journey. Was not doing it when i drove it a few days ago.

I just had a friend over who suggested disconnecting the camshaft position sensor (to run closed loop) and the misfire went away, reconnecting the sensor bought back the misfire.

Does this look like another bad sensor?...or should i do the system reprog you suggested Tim?

Is it true i need a special tool to align the camshaft sensor if i replace it?
Thanks for the fast reply
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Unread 08-01-2009, 06:50 PM   #4
CJ7-Tim
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Quote:
Originally Posted by nousernamesleft View Post
..... suggested disconnecting the camshaft position sensor (to run closed loop) and the misfire went away, reconnecting the sensor bought back the misfire.

Does this look like another bad sensor?...
The system re-boot is free and causes no harm.

By disconnecting the camshaft position sensor and having the misfire go away, one might assume that the cam sensor or the related wiring has issues. I would replace it. Just install a new one, no calibration or alignment needed.
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Between 2009 when Obama took office, and 2013, median annual household incomes have fallen by more than $2,100.

Progressive Liberalism: Bringing you new Healthcare ideas so wonderful, they have to include mandatory participation ......

Originally Posted by Ronald W. Reagan: Government is not the solution to our problems; Government is the problem.

Last edited by CJ7-Tim; 08-02-2009 at 10:07 AM..
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Unread 08-01-2009, 10:56 PM   #5
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Thanks Tim, that puts my mind at rest, advance will have one for me in the morning $59. I'll have a few threads i imagine. The vehicle was recently purchased and not in the condition the seller stated :+(
I'm happy to do the work as i learn as i go...i'm finding my way around Jags in the same forum manner.
I appreciate your help and as i get to know my way around will be contributing to threads.
I'll do the re-boot after i replace the sensor (tomorrow)...(almost today!)
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Unread 08-02-2009, 01:06 PM   #6
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so this morning i go out to pick up the sensor and the jeep won't start, turns over fine, sounds like no spark or no fuel. i pressed the schrader valve on the fuel rail, a little pressurised gas came out, tried to turn the engine over again and re-checked the shrader (no pressure tester here) again a little pressurized fuel, so i'm assuming fuel is getting to the rail. is it possible or probable that the camshaft sensor is causing this no-start?...coincidently the day after changing the crank sensor...i know a crank sensor can cause a no start, checked the crank sensor connector, checked and di-electric-ed the camshaft sensor electrical connector.
Advance auto failed to actually order the camshaft sensor, so it'll be a few day wait. I did the system re-boot...no difference, tried starting the vehicle with the camshaft sensor disconnected...no difference....now stumped
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Unread 08-05-2009, 01:24 AM   #7
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new cam sensor did nothing.
replaced the crank sensor with the old one...car started
new sensor lasted a whole 15 miles!
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Unread 08-05-2009, 08:13 AM   #8
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Quote:
Originally Posted by nousernamesleft View Post
...........new sensor lasted a whole 15 miles!
As you have just discovered, cheap automotive parts are cheap for a good reason. I don't buy no-name eBay parts or the crappy "Lifetime Warranty" parts from Advanced or AutoZone.

If you want good parts that will fit right, work right, and last, you need to buy brand name parts. I always get genuine JEEP sensors or NAPA and have never been disappointed.
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Between 2009 when Obama took office, and 2013, median annual household incomes have fallen by more than $2,100.

Progressive Liberalism: Bringing you new Healthcare ideas so wonderful, they have to include mandatory participation ......

Originally Posted by Ronald W. Reagan: Government is not the solution to our problems; Government is the problem.

Last edited by CJ7-Tim; 08-06-2009 at 08:52 AM..
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Unread 08-05-2009, 09:47 AM   #9
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i'll call a jeep dealer today and get one
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Unread 08-05-2009, 10:25 PM   #10
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If you have the time, Rock Auto has never given me any problems with their parts. Phil
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Unread 08-07-2009, 02:18 PM   #11
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got the sensor today from a dealership, put it in, runs fine no check engine light
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Unread 08-07-2009, 02:19 PM   #12
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$114 instead of $59 on ebay
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Unread 08-15-2010, 11:18 PM   #13
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Unread 08-16-2010, 10:30 AM   #14
tjwalker
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I've been working on XJs for a long time and the crankshaft position sensor is one part that I always purchase from the Jeep dealer.

Yes, it does cost more. But it will also last longer than (most) aftermarket parts and as it is a critical sensor that can leave you stranded, it is money well spent.
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Unread 08-23-2010, 01:41 PM   #15
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Will that cause an 01 XJ to just die as it going down the road? I didn't get a check engine light or anything? It won't restart and just sounds odd as it turns over.
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cam position , ckp , cps , crank position , p1391

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