Jeep P1391

[ChrisMc]

Woohoo for *Pending* check engine lights!

P1391 Intermittent loss of CMP or CKP

Any insight before I go replacing sensors?

1999 Jeep Cherokee
4.0l 5 Speed
216k

Cranks right up and runs fine for a minute or so, then all of a sudden the check gauges light comes on and the battery gauge is dead. It then doesn't like to accelerate. It accelerates but it sputters/bucks which isnt fun in a 5 speed (kinda embarrassing cause it looks like you cant drive). This happened a while ago and it got to the point it wouldn't even start. Turns out replacing the crank position sensor fixed that. I wont lie, I got a cheaper one off amazon so maybe that's the problem.

I was planning on doing a few things before I replace sensors. (make sure battery cables are fine, clean connectors, "famous jeep ecu reset")

Any other opinions? The battery gauge is whats confusing me

 

[mysterync]

Very common for loss of crank or cam sensor to cause charging issues in vehicles with pcm controlled fields - so that's not actually that abnormal. The easy checks are vref and ground at both sensors, and a resistance test of both signal wires from the sensor to pcm. Resistance isn't a very effective test, and isn't a verification that the circuit is good - but without some testing equipment it's your best bet. Also, it's wise to wiggle the wiring of the associated components and see if you can duplicate the issue.

 

[ChrisMc]

Update***

Got the jeep home last night (barely). On the way home all the electronics were dying, radio went out, lights got dim. Connected it to a good battery let it run and disconnected the battery and died right away. that told me it wasnt charging. Replaced the alternator and its all good now.

Thanks!