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  #1  
Old March 2nd, 2017, 08:32
58HalfCab 58HalfCab is offline
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P1391 Running Great

I recently finished a 96 XJ build. Stroker build with a 4.2 crank. Not sure what year the block is. At the time of the motor build I also swapped in an AX-15 transmission. I purchased a new 96 flexplate. Timing chain is new. I have built many motors. Took my time, checked all the measurements. Feel good about the build.

The jeep is running great. I put about 400 miles on it, changed the oil, and then drove it from my home in St. Louis to KOH, Moab, and back without any issues. The motor has tons of power and sounds great.

I need to pass an emissions test but have a check engine light on. P1391. Mismatch between the crank position sensor and the cam position sensor. If I erase the code it will stay off until the shortly after the 2nd start regardless if the first start is 1 minute or 1 tank of fuel.

First I replaced the Cam Position Sensor in the distributor with an auto parts store sensor. Didn't fix it. Replaced the Crank Position Sensor with an Auto Parts sensor. Didn't fix it. Got a Crank Position Sensor from the dealership. Didn't fix it.

Next I plan to get the cam sensor from the dealership. Any other ideas? I've got to be missing something here. The timing chain is not stretched. It's running too well for the timing chain to be off. There is no adjustment in the distributor without moving a tooth, which again it's running great.

Thanks for all the help!

-DJ
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  #2  
Old March 2nd, 2017, 09:09
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90xj06 90xj06 is offline
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Re: P1391 Running Great

P1392 is intermittent loss of Crank or cam signal if it was the crank sensor you would have some bucking and the rpm gauge would momentarily drop to 0. so it may be wiring to the cam sensor. not sure of the symptoms when that one disconnects when running. or possibly not aligned correctly.
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  #3  
Old March 2nd, 2017, 09:43
trippled trippled is offline
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Re: P1391 Running Great

Where did you get the flex plate? Seen a few mismatched ones causing odd problems
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  #4  
Old March 2nd, 2017, 12:08
58HalfCab 58HalfCab is offline
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Re: P1391 Running Great

Quote:
Originally Posted by trippled View Post
Where did you get the flex plate? Seen a few mismatched ones causing odd problems
Flexplate from o'reilly auto parts. I should be able to see the pulses from the sensors with my scanner. Does anyone have any data of what I should be seeing? I can replace the cam sensor then flexplate but replacing parts with hopes is not a cost effective troubleshooting.

Thanks again for all the help. I ordered a cam sensor from the dealership, it will be in tomorrow.
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  #5  
Old March 2nd, 2017, 13:18
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90xj06 90xj06 is offline
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Re: P1391 Running Great

Quote:
Originally Posted by 90xj06 View Post
P1392 is intermittent loss of Crank or cam signal if it was the crank sensor you would have some bucking and the rpm gauge would momentarily drop to 0. so it may be wiring to the cam sensor. not sure of the symptoms when that one disconnects when running. or possibly not aligned correctly.
sorry typo P1391
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  #6  
Old June 8th, 2017, 14:39
58HalfCab 58HalfCab is offline
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Re: P1391 Running Great

Still can't get the P1391 code to go away. I have crank and cam sensors from the dealership. Still have the oreilly's flywheel. Engine still runs great. I visually inspected the wiring and did not find any areas of concern. everything except the actual transmission is for a 96. Flywheel, Crank Position Sensor, Cam Position Sensor, ECU. The ECU is still the stock unit from the Automatic but everything I read says that the ECU will not matter as the transmission was not controlled by the ECU in 96.

There is no way it is either sensor as they have both been replaced multiple times. I have thought about opening up the holes on the crank sensor and adjusting the clearance between the sensor and the flywheel but I can not find specs on what the clearance should be.

The transmission is coming out Sunday for a rebuild. I am tempted to buy a second flywheel and see if that fixes the problem. Only other ideas are run new wires for both the crank and cam sensors to the ECU. I had one suggestion to replace the distributor.

Again it is running great. What would you do?
- Source an ECU for a 96 with a manual.
- Try a second new flywheel, assuming something is wrong with the new one I have.
- Run new wires to the crank position sensor.
- Run new wires to the cam position sensor.
- Open the holes in the crank sensor and play with the clearance between it and the flywheel
- Replace the distributor.

Thanks for the help!
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  #7  
Old June 8th, 2017, 15:20
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Tim_MN Tim_MN is offline
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Re: P1391 Running Great

I suggest using only genuine Jeep OBD sensors and having the Camshaft Sensor Synchronization checked/set with a DRB-III Scan Tool or an oscilloscope.

Be sure to read the linked info -

http://www.jeepforum.com/forum/f19/j...e-fix-3487474/

Scan Tools, O-Scopes and Toothpicks >> http://jeep.blackonyx.net/pdfs/jcss.pdf



P1391 - Intermittent Loss of CMP or CKP Signal. Loss of the Cam Position Sensor or Crank Position sensor signal has occurred.

P1391 – Possible symptoms:
(1) random misfire/stumble/bucking/stalling, often over bumps or right hand turns or when going into reverse.
(2) shorted out the Fuel pump/ECU power wire.

Possible causes
- Faulty Camshaft Position (CMP) Sensor
- Camshaft Position (CMP) Sensor harness is open or shorted
- Camshaft Position (CMP) Sensor circuit poor electrical connection.
- CMP SENSOR OUT OF SYNC
- DAMAGED TONE WHEEL/FLEX PLATE (CRANKSHAFT)
- DAMAGED TONE WHEEL/PULSE RING (CAMSHAFT)
- IRREGULAR LAB SCOPE PATTERN OF CMP SIGNAL
- INTERMITTENT CKP SIGNAL LOSS WHEN WIRING IS WIGGLED
- IRREGULAR LAB SCOPE PATTERN OF CKP SIGNAL
- WIRING HARNESS INTERMITTENT
- INTERMITTENT CMP SIGNAL LOSS WHEN WIRING IS WIGGLED
- CRANKSHAFT POSITION SENSOR CONNECTOR/WIRING
- FAULTY CRANKSHAFT POSITION SENSOR


Potential Fixes:
Fix #1:
Inspect your wire harnesses for damaged wires, chafed insulation, or failed wire splices. Use a volts/ohms multi-meter to check the resistance of the ground wire circuits from each sensor. Replace corroded ground wires/connectors and clean ground wire connection points.
Fix #2:
Timing may off. Re-index the distributor/cam sensor per the FSM instructions, or replace faulty distributor/cam sensor pickup module.

A mis-indexed distributor/cam sensor may exhibit surging, light bucking or intermittent engine misfiring. This will most likely occur when the vehicle is at operating temperature and under a light load at approximately 2,000 rpm. The proper indexing procedure must be used as outlined in the service manual.
__________________
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Quote:
Originally Posted by bimmerjeeper

I'm starting to realize people on the Jeep forums are highly expert mechanics .....

Last edited by Tim_MN; June 8th, 2017 at 15:29.
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  #8  
Old June 8th, 2017, 15:49
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four_shot four_shot is offline
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Re: P1391 Running Great

Is there any way to check the run out on the flywheel tone ring? I'm wondering if its not defective.
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  #9  
Old June 16th, 2017, 08:28
58HalfCab 58HalfCab is offline
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Re: P1391 Running Great

PROBLEM FIXED.

I saw the post about moving the cam position sensor and since I still had the one I bought from the auto parts store i figured I would give it a try.

I cut the 2 tabs off the sensor that the distributor cap screws go through. I then took the sensor to a disk sander and removed the material around the wire that locks the sensor into the actual distributor housing. I installed the modified cam position sensor with it offset clockwise from the stock location. Ran like shit, light came back on. Pulled the cap and went the other way. I did not move it much. The wire is still coming out of the distributor opening but with the plastic removed I can go about 1/4" each way. The second try I had the cam position sensor counter-clockwise of the original location.

No check engine light! Drove it for a 100 miles and then PASSED the Illinois Emissions Inspection! Now have 600 miles on it and all is good.

I suspect this was caused by the 4.2 crankshaft and aftermarket camshaft combination. I told my roommate about the fix and he mentioned that a lot of stroker builds switch to an adjustable timing set up front. That would probably be the correct way to address this issue, I'll get to that at some point in the future.

For now I have legal plates and am daily driving it with confidence! Thanks for all the help and input ! If you're fighting a similar issue shoot me a PM and I would be happy to help.
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