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P1391 code, ckp/cmp

4x4JeePmaNthINg

NAXJA Forum User
Location
Colorado
99 jeep xj 205000

I was just driving yesterday and now I have a p1391 code that has the CEL on AGAIN. AZ printout shows this code to be CPS or CKP.

very recently I had CEL with a p0340 code and I just replaced the Cam position sensor, the CEL then disappeared.
Before that Ive had a battery temp sensor light that brought the CEL up off and on over the past few months. I havent replaced this one, but I did pull it and tape/solder some exposed wire and added some dielectric grease to the plug which seems to have worked, but I still plan on replacing this sensor anyway.

both cam/crank sensors are Mopar, the cam about a week old and crank sensor about a year old.

This is very odd that I keep getting these codes with a CEL light as of recently. The only thing I can figure as a common trait between the battery temp sensor and the new CEL is it had rained out. The jeep seems to be driving just fine, Im curious if the CEL will shut off on its own...

last time before replacing the CSPS I let the jeep run and carefully wiggled many wires/plugs around to see if I could get any odd responses, but nothing was noticed.

I plan to visually inspect the undercarriage tomorrow

is there anything in particular that will start spawning CEL this often?

im not quite sure where Ide start to check this because it seems too soon to have an issue with either of these sensors right?
 
What diagnostic testing and trouble shooting have you performed to find the root cause of the Trouble Codes ? Did you install a genuine Jeep sensor or some crappy Chinese clone part with a "Lifetime Warranty" ?

P1391 JEEP - CMP or CKP Signal Intermittent Condition
Possible causes

•Faulty Crankshaft Position Sensor (CKP)
•Crankshaft Position Sensor (CKP) harness is open or shorted
•Crankshaft Position Sensor (CKP) circuit poor electrical connection
•Timing belt or chain stretched or jumped
•Faulty Camshaft Position (CMP) Sensor
•Camshaft Position (CMP) Sensor harness is open or shorted
•Camshaft Position (CMP) Sensor circuit poor electrical connection.

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. Read this thread >> http://www.jeepforum.com/forum/f19/...352-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 Jeep Service Manual.
 
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I have more to research on diagnosing this CEL that appears and disappears, but I have a question regarding the installation of a Crank position sensor.

The newer mopar sensor was installed about a year ago. IF this was to have been installed too low/ touching the flex plate, would this be an issue that could hide for a long while, or would this be immediately noticed?
 
If it was to low it would hit the flex-plate and you would have heard it right off!
 
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.

Is there a diagram of this ground circuit available? Does the FSM label every prong on the plugs to the wiring harness?
 
Also make sure you measure wire to wire resistance, that's where most of my wiring went bad!
 
Had this code intermittently on a '96. Was pulling hair out. New CKPS hard wired in. Newish entire distributor. Read toothpick and oscilloscopes. Does not apply to my distributor, interesting lesson though. However upon opening distributor found some gunk/buildup in sensor airgap and dirty rotor. Internal cap electrodes also very crusty. Cleaned everything up and reassembled. No more dtc. Gave it a couple days and rewarded the good jeep with a new brass electrode cap and some champion coppers. Yummy.
 
I haven't check the distributor yet, but this code keeps disappearing and reappearing every now and again. I'm wondering if the timing chain has any part in this.
 
It seems logical that distributor or distributor-less, checking the synchronization of the CPS and Cam Sensor signals is a good idea if the P1391 code is/was present. A stretched timing chain can change the signal synch.
 
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Typed a nice story about the 3000 mile trip with 1391, but lost it when I had to log back in.
Question was, does Cruiser54's indexing procedure for renix work for HO 4.0's as well?
 
Seems to have worked BEAUtifully. A week of DD commute(40 mi each way) and no more 1391. No more pesky light at all. Better seat of pants take off as well. I would highly recommend anyone That does a build that ends you up with a new cam and distributor to at least check their indexing. When I put on the windowed dizzy and brought it up to TDC my rotor was just starting to make contact, instead of being at the trailing edge. It took 40000mi on this build before it threw the 1391. I had no idea I was missing out.
Not bad for an old rig, 1996 Country, 356728mi and counting.
Much love to the NAXJA!
 
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