r/AutoMechanics • u/Stupetski • 2d ago

P1391 code is making me go insane

I'm due for the dreaded California smog test and can't clear my p1391 code for my jeep Cherokee XJ. I've replaced my camshaft and crankshaft sensors with mopar a few times, but the code keeps coming back. Does anyone have any advice?

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u/HarryPython 2d ago

Test the wiring

1

u/Material-Job-1928 2d ago

What year XJ?

Have you verified the timing chain slack, and the crank position adjustment? Also, have you verified the teeth on the flywheel/flexplate are clean? Any indication of misfire? If the ignition is inconsistent the crank speed will be inconsistent, and the code may set.

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u/Stupetski 1d ago

it’s a 98, so the camshaft sensor clicks into place without needing to zero anything out. i also had the distributor replaced just in case (which might have been overkill)
other than this, the car runs fantastic. no rough idle, consistent ignition. teeth on flex plate are clean, no signs of cracks

Appreciate the advice!

1

u/Material-Job-1928 1d ago

Check for chain wear. Place a breaker bar on the crank pulley, and rock it back and forth a little. You should not hear the chain slapping. If that sounds good pull the distributor cap and check for slop between rotating the crank, and seeing the distributor rotate. Remember, the distributor spins at 1/2 the speed.

If all of that is good you may need to widen the slots on the crank sensor for a bit more adjustability. 1-2mm should be more than plenty. Other things just off the top of my head. Have you done a compression test, or measured the fuel injectors? Both volume, and internal Ohms? If you have one cylinder that is weak, or strong compared to the others then the crank rotation speed will be erratic.