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  #1  
Old December 6th, 2017, 13:13
wes3337684 wes3337684 is offline
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P1391 stumped

Hi everyone long time looker first time poster, I have a 98xj 4.0 Auto, its got 283k on it with only minor issues like freeze plug leaking into bell housing . Now I have the p1391 code, put in new Mopar crank sensor still have code, put in new Mopar cam/ pick up sensor coil, still has code. Checked wiring to o2 sensor ect. and all grounds. Put #1 at TDC with harmonic balancer on TDC and pin fits like a glove into slot in distributor with no play in shaft. What am I missing? SES light comes on as soon as i start it twice, but runs fine. I can unplug crank sensor with jeep running and it kills the engine, unplug cam sensor engine stays running.
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  #2  
Old December 6th, 2017, 19:23
blakews2217 blakews2217 is offline
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P1391 stumped

Quote:
Originally Posted by wes3337684 View Post
Hi everyone long time looker first time poster, I have a 98xj 4.0 Auto, its got 283k on it with only minor issues like freeze plug leaking into bell housing . Now I have the p1391 code, put in new Mopar crank sensor still have code, put in new Mopar cam/ pick up sensor coil, still has code. Checked wiring to o2 sensor ect. and all grounds. Put #1 at TDC with harmonic balancer on TDC and pin fits like a glove into slot in distributor with no play in shaft. What am I missing? SES light comes on as soon as i start it twice, but runs fine. I can unplug crank sensor with jeep running and it kills the engine, unplug cam sensor engine stays running.


Do a reset on the ecu. I hook the battery + cable and ground it out ( can be on the ac compressor ) for 30 seconds. Put it back on. Turn the key to on but donít start. Turn the headlights on for 10 seconds, then off. Now start. It will relearn over the next 50 warmups.


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  #3  
Old December 7th, 2017, 04:47
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Tim_MN Tim_MN is offline
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Re: P1391 stumped

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/stalling, often over bumps or right turns and 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.

Symptoms:

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
-SENSOR CONNECTOR/WIRING
-CAMSHAFT POSITION SENSOR
-CKP SENSOR CONNECTOR/WIRING
-CRANKSHAFT POSITION SENSOR


Often replacing the sensor fixes this code, but not necessarily. Therefore it's important to check the following:


•Check that the wiring isn't routed too close to sharp metal edges, or to hot exhaust parts.
• Visually inspect the wiring at the sensor for any burn marks, discoloration indicative of melting or chafing of insulation
• Visually inspect the cam sensor for damage
• Visually inspect the reluctor wheel inside the alternator. Make sure the magnet is firmly attached.
• If all checks out okay, then replace the sensor.

If you buy any OBD-II engine sensors, make sure to buy genuine Jeep sensors.

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.


Google Scan Tools, O-Scopes and Toothpicks, and read the article.

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 Jeep Service Manual.
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  #4  
Old December 7th, 2017, 17:16
wes3337684 wes3337684 is offline
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Re: P1391 stumped

Reset the ecu, code came back 2nd time I started the engine. What should I try next? The distributor doesn't have any side to side play only some play when I try to turn the rotor back and forth and I can't find any info about how much play in allowable, should I replace to distributor??
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Old December 8th, 2017, 11:14
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90xj06 90xj06 is offline
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Re: P1391 stumped

did you remove the distributor when you did the sensor?

is it running good? any symptoms?
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  #6  
Old December 8th, 2017, 17:17
wes3337684 wes3337684 is offline
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Re: P1391 stumped

No didn't remove the distributor to install the cam sensor.
Runs fine only a slight miss at idle in drive that I can feel and see in the tech moving ever so slightly.
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Old December 12th, 2017, 21:28
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Runnin'OnEmpty Runnin'OnEmpty is offline
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Re: P1391 stumped

Quote:
Originally Posted by wes3337684 View Post
No didn't remove the distributor to install the cam sensor.
Runs fine only a slight miss at idle in drive that I can feel and see in the tech moving ever so slightly.
A weak ignition coil will cause a miss at idle even though the miss goes away when revs increase. The generic code
P1391 is also related to the ignition coil.

I'd do an ohms check of the coil windings. While you're at it check the coil to distributor wire (should be about 5-10K ohms).
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  #8  
Old December 11th, 2017, 14:52
wes3337684 wes3337684 is offline
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Re: P1391 stumped

I tried to check for timing chain slack, I put #1 at TDC and the harmonic balancer there also, then slowly turned the crank the opposite direction til the rotor turned. Looks like I had to move the crank to the 5 degree mark until the rotor began the turn. I that to much play?? Can't find a spec on it.
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