Dreaded crank and cam shaft sensor problems.

[Keith1187]

After fixing the rear axle in my 2000 Jeep Cherokee I went to pull it out of the garage and it had an extremely rough idle and it would die. It originally threw the code p1391. After looking it up on the inerwebs I found it can be either caused by the crankshaft or cam shaft position sensors going bad. So I ran out and grabbed a camshaft position sensor since the crankshaft was a mopar one I installed a few years ago. This did not solve the problem. I did confirm the cam shaft is in sync by setting the engine at TDC and the holes on the cam shaft sensor shaft thing (The thing the distributor would mount to) aline.

So I broke out the multimeter and tested to make sure everything was getting its 5 volt feed along with a good ground and the 5 volt from the computer through the signal wire. I tested the cam, crankshaft and tps since they are on the same circuit for the computer. Everything checked out. So I decided to replace the mopar crankshaft position sensor with a parts house one. Just as a temporary solution. This did not fix the issue instead it started throwing a p0122. Tps circuit low code.

At this point I'm lost so I decided to clean every single ground. With a wire wheel in a drill. I cleaned the two under the ac compressor, the ribbon, and the one by the battery. Still no change in the idle or codes. So I continue to do some research I found a similar thread and the cause was his tcu was coroaded. This morning I pulled my tcu and cleaned the connecter with electrical parts cleaner. I also cleaner a ground that was under the dash. The jeep ran the same with the tcu plugged in and unplugged in. And the same after it was cleaned. Then I unplugged the ECU/PCM and cleaned the plugs. The issue still presist with both codes being thrown.

At this point I'm leaning towards the pcm or tcm being bad. Any advice or anything else to check?

 

[RCP Phx]

While they all receive power from the same source it's the the return signal voltage that counts and a oscilloscope is best at that to "piggyback" while running!

 

[Unclewolverine]

I didn't see where you replaced the tps, which is always the #1 suspect for running issues.

 

[Keith1187]

I didn't see where you replaced the tps, which is always the #1 suspect for running issues.

Sorry, I forgot to add that part. I have since replaced the tps even though it sent the correct voltage range through the signal wire when I manually slowly opened and closed the throttle body.

 

[Tim_MN]

Some P1391 notes I have gathered:

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
• 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.
• 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.