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Bogging, hesitation, rough idle, CEL

Tim_MN said:
The cam and crank sensors should be free of grease, oil, and debris.

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 CamshaftPosition (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 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.
Click to expand...

Hello every one, I have a 4.0 97 Xj std trans with about 230K miles, and have around three months having problems with codes P0320 and P1391, have done almost all of the above, the only two thing I haven't done is the alternator and timing tests, from there on all has been checked.

Haven't done the alternator because it's practically new, two years since I replaced it. And timing because I recently replaced the distributor withe a new one. Since the old one had a bad seal or bushing and oil was coming in. I'm sure the new ones is correctly installed, but I'm going to double check.

Sincerely I'm frustrated, it's my DD and weekend warrior, so I'm stranded without my Xj working accordingly. HELP is appreciated!!
 
The_97_Sport said:
P0135: O2 (B1S1) Heater Circuit
P0141: O2 (B1S2) Heater Circuit
Click to expand...

When my 1997 XJ had the same code, I found the O2 heater ground to be loose. It's connected to one of the ground studs, located next to and just forward of the passenger's side motor mount.
 
The_97_Sport said:
I checked the voltage at the battery during idle and the multimeter read 14.1 to 14.2V.
when the idle bogs down it drops to about 13.1ish, but then jumps right up to idle speed again and its back to 14.1/14.2. It seems the drop in voltage is most likely due to the idle's sudden drop, but heres my questions:
1. could this sudden RPM drop be due to the alternator?
2. would turning on all electrical such as rear defrost, A/C, radio and brights be similar to load testing?
3. Would a weak alternator cause an intermittent CMP or CKP code?
This weekend i am going to make sure all electrical connections are nice and tight and clean all of the grounds and completely test the alternator.
Click to expand...

I would suppose that the idle drop is symptom of the problem, and not a cause. Load testing of the battery/alternator needs to done with proper test equipment. Low battery voltage due to battery/alternator/wiring issues can cause all kinds of problem and strange behaviors.



mayub78 said:
Haven't done the alternator because it's practically new, two years since I replaced it. And timing because I recently replaced the distributor withe a new one. Since the old one had a bad seal or bushing and oil was coming in. I'm sure the new ones is correctly installed, but I'm going to double check.

Sincerely I'm frustrated, it's my DD and weekend warrior, so I'm stranded without my Xj working accordingly. HELP is appreciated!!
Click to expand...

New or recently replaced, you still have to inspect and test things to confirm they are in good condition, installed right, and working correctly.
 
Last edited:
So, to update you all.

First of all, thanks for all of your help!!

I had done a lot to my Xj, pulled the engine harness strip it all to look for bad wires, loose connections, bad or corroded connectors, changed the CMP and the CKP with OEM parts, check timing that by the way had to strip the front to get all the way to the timing chain just to be sure that it hadn't stretched and started to jumping the sprockets, checked the alternator, battery........and was about to quit....!

So, a last visit to the mechanic to reset the ECM all the way to factory setup, he pulled the distributor cap off to check if the rotor was nos loose. I had an old pick up coil and rotor with me, so changed them, because I was going to return the OEM CMP for a refund. Since I still had the codes P0320 and P1391. reset the computer, turn on my jeep on and no codes, drove for some miles and just like if nothing had been wrong.

So just for the record, OEM parts can also fail brand new. have been driving my Xj for about a week now and no codes, no problems.

Thanks ones again for the help! Now to enjoy my Xj!!
 
Hello everyone, another update to my last update.

So a few weeks gone by the check engine light came on again. Same code, no misfire, nothing wrong, all working properly. So I left it like that as long there were no problems.

Time went by and a tune up time arrived. Changed oil, filters, cleaned injectors, changed spark plugs.

When changing spark plugs I checked the gap opening on the old ones and assured the new ones went in with the manufacture spec gap. Reset the computer.

WALA, no more codes, no more check engine light. It ends up that the old plugs hade variable gaps and spark was not the same on all of them.
 
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