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1996 4.0 4wd Jeep xj p1391 code.

Brayden96xj

NAXJA Forum User
96 Jeep xj having a p1391 code I’ve changed every it’s act like it shuts off and starts back up randomly. I’ve changed cps(with mopar one) cam sensor,throttle body and all those sensors, cap plugs wires rotor and distributor. And fuel pump and filter. Also tried different computer. I’m lost
 
That would suggest a wiring issue!
 
P1391 - Intermittent Loss of CMP or CKP Signal. Loss of the Cam Position Sensor or Crank Position Sensor signal has occurred.

P1391 JEEP Possible Causes
- Faulty Crankshaft Position Sensor (CKP)
- Crankshaft Position Sensor (CKP) wire harness is open or shorted
- Crankshaft Position Sensor (CKP) wire circuit poor electrical connection
- Faulty Camshaft Position (CMP) Sensor
- Camshaft Position (CMP) Sensor wire harness is open or shorted
- Camshaft Position (CMP) Sensor wire circuit poor electrical connection.

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.
(3) A improperly 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.

Often replacing the faulty sensor fixes the P1391 code, but not necessarily. Therefore it's important to check the following:
• Check that the Cam and Crank sensor 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, bare wires, or discoloration indicative of melting / chafing of insulation, and other damages.
• Visually inspect the cam sensor for damage. Make sure the magnet is firmly attached. The sensor can be tested.
• Visually inspect the reluctor wheel inside the distributor or Cam Sensor.
• Inspect the distributor assembly for excessive wear.
• If everything checks out okay, then test the Crankshaft Position Sensor.

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

Potential Fixes:
Fix #1:
Inspect your O2 wire harnesses for bent or pushed back wire plugs pins, 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:
The timing may off. Re-index the distributor/cam sensor per the FSM instructions, or replace faulty distributor/cam sensor pickup module.

Read this article: Scan Tools, O-Scopes and Toothpicks here >> https://web.archive.org/web/20200820085756/http://jeep.blackonyx.net/pdfs/jcss.pdf
Read this thread >> https://www.jeepforum.com/forum/f19...352-p0353-crank-cam-sensor-issue-fix-3487474/

Testing the Throttle Position Sensor and Coolant Temperature Sensor is also a good idea.
 
I’m gonna try to check the wiring. It doesn’t have the rear o2 sensor hooked up but my last Jeep never had it either. My symptoms are rough idle and the engine intermittently cutting out under load. The warmer the motor gets the worse it is
 
I’m gonna try to check the wiring. It doesn’t have the rear o2 sensor hooked up but my last Jeep never had it either. My symptoms are rough idle and the engine intermittently cutting out under load. The warmer the motor gets the worse it is
I don’t think a down stream o2 would cause it to shut completely down and pick back up
 
.02 (just did this 2 weeks ago)

When my downstream o2 sensor failed, engine ran rich and stumbled all over itself. Gas mileage dropped.
Replaced and purring like a kitten again. Had to buy a cat (rockauto ~$140) too.
There is a specific error code for downstream o2 sensor that wont change voltage.
 
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