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P1391, What the ?

ahm

NAXJA Forum User
Location
Long Island NY
Trouble code P1391 - Loss of CMK or CKP ??

Does anybody know what this is?:tears:

The truck will run fine until you rev engine up to 2000rpm the engine will drop to 200rpm and giving it throttle wont do anything.
 
Thank you, thats what I was thinking but wasnt sure.
The XJ runs good sometimes, the loses all power till i turn off & restart.
 
Sorry about the way these look, but I couldn't copy and paste them so I took screen captures.
1391a.jpg

1391b.jpg

1391c.jpg

1391d.jpg

1391e.jpg

1391f.jpg
 
This info is great, thank you very much.
I just went out & purchased 2nd CPS($106) to ind out thats not the problem. W/this info i can do more testing and less spending.
thank you
 
This is copied from my 1999 F.S.M. I don't know if this will help or not (hope so).
"ENGINE START-UP MODE
This is an Open Loop mode. The following actions occur when the starter motor is engaged. The powertrain control module (PCM) receives inputs from:
² Battery voltage
² Engine coolant temperature sensor
² Crankshaft position sensor
² Intake manifold air temperature sensor
² Manifold absolute pressure (MAP) sensor
² Throttle position sensor (TPS)
² Camshaft position sensor signal
The PCM monitors the crankshaft position sensor. If the PCM does not receive a crankshaft position sensor signal within 3 seconds of cranking the
engine, it will shut down the fuel injection system. The fuel pump is activated by the PCM through the fuel pump relay. Voltage is applied to the fuel injectors with the ASD relay via the PCM. The PCM will then control the injection sequence and injector pulse width by turning the ground circuit to each individual injector on and off. The PCM determines the proper ignition timing according to input received from the crankshaft position
sensor."
 
Thanks for info,
The fuel pump is still running, it seems to be pumping fuel like its running, strong smell of gas. Wont start. I couldnt locate another coil pickup(CPS), i think my new one is bad.
 
I Need it.
Well Jeep looked at for 2 hrs and have no idea what it could be. They told me they can cont. to look at but it will get very expensive($98hr). I picked it up and i'm going to check wiring, Jeep said the sensors(Cam & Crank) are good and the timing was good.
Start there first.
 
Similar problem here. Both sensors are ok. Loss of signal above 2K. Has something to do with the two signals being out of sync. I only get a CEL, no shutdown.
I will post when I discover more.
Rick......
 
In thinking more about this, and please note that I'm just beginning to learn about engines and transmissions, is it possible that a cracked flexplate on an auto. or a bad flywheel on a manual could cause the CKP to send a bad signal?
 
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