P1391 99 Jeep xj 4.0 auto

Hello,

99 jeep cherokee auto 223,000 body, 30,000 motor

I have a P1391 code with a check engine light, the light returns every second start if i clear adaptive memory.
all sensors are mopar factory sensors, Cam position sensor and Crank shaft position sensor are mopar, about 1.5yr old
this code existed before engine swap, all new parts replaced after swap. the vehicle starts, runs and drives strong. idle may have misfire but the bluedriver scanner i had borrowed did not read any.

What I have tried thus far:

- Point to point continuity and voltage reading from back probing each sensor at the harness, signal, 5v supply, ground, as well as read from back probing the PCM. tested crank and cam signal with key on and cranking, analog meter used to view signal fluctuation. wiggle all wires while testing, looked for splits/corrosion.
-CKP ohm tested
- New Ignition coil, New alternator, engine( replaced with rebuilt from local, expected 25,000-30,000 miles on before sale- orignal motor main bearings failing, New Throttle position sensor (replaced for p1022 throttle position sensor "A" circuit low), New Distributor ( replaced to rule out bad gear) no change after all these oarts ( they all needed upgrade anyway)
- Dry compression test 128-135PSI, pressure holds until gauge is released
- vacuum at idle 14bar
- fuel pressure test and bleed down, 45 psi
- fuel injectors ohm tested, all good
- all grounds tested to battery
- test light on battery short circuit test, didn't illuminate
- all continuity testing .5-.8ohm, on all sensor 5v,signal,grounds and battery ground to block grounds

without a scope i had to bring it to a local shop for a Diagnostic, the results of which they reported:
- CMP/ CKPS sensors are in sync
- all sensor readings are getting to the PCM
- after clearing the code it continues to return the CEL every second start just as ive had it do
- no misfires were counted on their computer
- they reported they believe 99% this is a PCM issue and couldnt say 100% until a new PCM was tried.

What ive tried and have since found out:
- Junk yard PCM aquired from matching year and the PCM numbers match
- disconnected battery- doing so CEL disapears (adaptive memory i assume), installed donor PCM, the jeep fired right up as usual, let it warm up to operating temp, shut down to restart a second time, CEL returns like normal.
I haven't had this CEL to make sure its the same, but i figure it firing a code upon this trial is a little too coincidental for it coming on as it always has. I can go to AZ and have it read, i dont have the borrowed bluedriver scanner anymore.


Ive been pulling my hair out on this one folks, I dont know what to try next and Im here seeking your help!

what should I try next?


PLEASE and Thank you all!!!

P1319 is cam/crank related. I would start by checking your base timing and checking your timing chain. Other than that cam and crank sensors and electrical connections for the cam and crank sensors should be checked.

is checking the "base timing" the same as positioning the harmonic balancer to 0 degree on the cover and turning counter clockwise until i see the distributor rotor turn?

This code can definitely be frustrating to chase. But hey, look on the bright side! It's a hard fault. :silly: No test driving or intermittent BS to chase. This is genuinely to your advantage.

With respect to the shop you took it to, but I think you need to start from scratch. If the CKP and CMP signals were truly in sync, with no glitches or faults, you wouldn't be getting this code.

However, without a scanner or scope, diagnosing this one will be tough. If this were in my bay, my first move would be to use the Set Sync bidirectional test to see what the PCM thinks the difference between CKP and CMP is. This procedure is required any time the CMP gets replaced, and should read zero or close to it. If it doesn't, you can adjust the CMP sensor during the test to get a zero reading.

A BlueDriver or the like won't have this function, only a factory capable scanner like an Autel/Snap-On/Launch/Bosch, or the Chrysler DRBIII itself. The other option you have is to get a dual channel lab scope to check the signals yourself. That'll allow you to verify good waveforms from the sensors, AND at least get the CKP/CMP sync close if it's significantly off. We can find you a known good waveform to compare to if needed.

As far as just reading codes, don't worry! Chrysler/Dodge/Jeep products of this generation will read them out for you. Just turn the key from Off to Run three times (without cranking the engine), ending in Run. Any stored codes will show up on the odometer display.

Tyler wrote: This code can definitely be frustrating to chase. But hey, look on the bright side! It's a hard fault. :silly: No test driving or intermittent BS to chase. This is genuinely to your advantage.

With respect to the shop you took it to, but I think you need to start from scratch. If the CKP and CMP signals were truly in sync, with no glitches or faults, you wouldn't be getting this code.

However, without a scanner or scope, diagnosing this one will be tough. If this were in my bay, my first move would be to use the Set Sync bidirectional test to see what the PCM thinks the difference between CKP and CMP is.
this requires the scope correct? also the shop offered to refund me for not being able to fix this, they felt strongly over not believing hooking up again they would find anything,though they were happy to try. instead of getting my money back, I have asked if I could get them to attach the scope again and if I could then get photographs of the cam/crank signals together. Im waiting to here back on this.
This procedure is required any time the CMP gets replaced, and should read zero or close to it. If it doesn't, you can adjust the CMP sensor during the test to get a zero reading.

how is this set to read zero, a cam sensor is a simply replacement, ive reindexed the mopar dizzy and the replacement dizzy in accordance with the field service manua multiple times l might add, are you referencing another procedure?

A BlueDriver or the like won't have this function, only a factory capable scanner like an Autel/Snap-On/Launch/Bosch, or the Chrysler DRBIII itself. The other option you have is to get a dual channel lab scope to check the signals yourself. That'll allow you to verify good waveforms from the sensors, AND at least get the CKP/CMP sync close if it's significantly off. We can find you a known good waveform to compare to if needed.
the shop did use a snap on scanner, bigger than the verus he said. i might be able to ask someone about the DRBIII but its not promising. with a two channel scope how will i be able to verify the signal patterns without an overlay of the 4 channel scopes ability? I dont mind the shop scanning if they know what they are reading, this place ought to, they have many jeeps even though they do not specialize in them, they are very familiar so they say and ive seen many there. im kinda at the mercy of my not having the tooling to look at the needed details here

As far as just reading codes, don't worry! Chrysler/Dodge/Jeep products of this generation will read them out for you. Just turn the key from Off to Run three times (without cranking the engine), ending in Run. Any stored codes will show up on the odometer display.

this trick does not work on the 99 jeep cherokees, i believe it was on newer models. the only code the blue driver showed, and AZ a week ago was p1391.

based on what youve said above, we need to start with a reliable scope diagnostic yes? if i look elsewhere for someone to run this what should i make sure they know?, or should i just take it to chrysler?

Does the DRBIII show cam and crank signals?