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paroxysym
September 18th, 2017, 18:54
I'm currently looking at purchasing another XJ. I've come across a very clean 97 4.0, only problem is it currently has a CEL. According to the seller there is no signal to the crank sensor, or the cranks no sensor isn't linked to the PCM. He has replaced his crank sensor but says it's still not registering, he thinks it's the PCM. It runs and drives fine he says. I am going to look at it this weekend, but before I make an offer I'm just seeing what possibly could be the issue and how big a fix is it.

The jeep has 175k on it

md21722
September 18th, 2017, 20:36
A complete diagnostic will tell you what's going on. I may be defective PCM, crank sensor, or wiring in between.

Tim_MN
September 19th, 2017, 03:53
If there is no signal to the Crank Position Sensor, it likely would not run at all. If it runs and drives, and the price is right, buy it. Purchase an OBD-II trouble code reader and a genuine Jeep Service Manual. Troubleshoot and fix the CEL. I once bought a 99 that wouldn't start for $800, fixed in in two hours, and sold a few days later for $2800

paroxysym
September 19th, 2017, 04:23
If there is no signal to the Crank Position Sensor, it likely would not run at all. If it runs and drives, and the price is right, buy it. Purchase an OBD-II trouble code reader and a genuine Jeep Service Manual. Troubleshoot and fix the CEL. I once bought a 99 that wouldn't start for $800, fixed in in two hours, and sold a few days later for $2800

yea guy drives it everyday. super clean 97 with 175k, $3k.

90xj06
September 19th, 2017, 09:52
if its running then it might be the cam sensor that's throwing a code. it would be in the distributor. if it is for the crank sensor it may have been a old code that has not reset yet.

paroxysym
September 20th, 2017, 04:16
talked to the owner its a P1391 code, after doing some research it doesn't seem like THAT big of a deal

Tim_MN
September 20th, 2017, 15:57
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 Cam Position Sensor SIGNAL
- INTERMITTENT CKP SIGNAL LOSS WHEN WIRING IS WIGGLED
- IRREGULAR LAB SCOPE PATTERN OF CranK Shaft Position SIGNAL
- WIRING HARNESS INTERMITTENT
- INTERMITTENT Cam Position Sensor 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.

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

*http://www.jeepforum.com/forum/f19/jeep-4-0l-p1391-potentially-p0351-p0352-p0353-crank-cam-sensor-issue-fix-3487474/

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.