code 1391

I am having an occasional backfire and miss while driving down the road. Other than that it runs great 90% of the time. It is a 96 xj 4.0 auto. I also have a IAC code and an Engine temp high input code as well. any advice?

Engine high temp input will be an unplugged, bad coolant temp sensor in the t-stat housing, or wiring. Car will run extra rich with it unplugged and unused gas will backfire in the exhaust. IAC code could be from a dirty IAC(pull off throttle body, remove two torx bits holding IAC, remove and clean it good w/ sensor safe cleaner).

The 1391 code is for the cmp or ckp.. I didn't think that the crankshaft sensor had occasional failures, I thought it would just fail completely.. any advice?

wingnut87 said:

The 1391 code is for the cmp or ckp.. I didn't think that the crankshaft sensor had occasional failures, I thought it would just fail completely.. any advice?

Click to expand...

They can fail catastrophically or they can be intermittent and give you some time to test and replace if necessary........nudge, nudge.......!

Crank sensors are a more common failure than the cam sensor in my experience but this code can absolutely be related to either.

well I just put in my spare crankshaft sensor and the problem still exists.. I checked all of the wires and all seems ok.. I guess it is time for a cam sensor because the problem is getting worse every time I drive it.

1391 Intermittent loss of either camshaft or crankshaft position sensor.

The cam sensor is the dist pickup. Possible like my friends the upper dist bushing is bad allowing the dist to contact the pickup and causing your problem. Pull the dist cap and see if the rotor/shaft has excessive play side to side.

wingnut87 said:

well I just put in my spare crankshaft sensor and the problem still exists.. I checked all of the wires and all seems ok.. I guess it is time for a cam sensor because the problem is getting worse every time I drive it.

Click to expand...

I had that same code 1391 when I was in Miami in July. That code seem to indicate that the 4.0 had a problem with the timing/ loosing timing. It turnned out to be the O2 sensor. The engine would run good when cold but progressively get worse until the engine would shut down.

When the engine is cold, the O2 sensor would be ignored by the PCM. As the engine warmed, the PCM will read the O2 and adjust the timing for optimun performanance. Using the Scanguage, I noticed the timing moving all over the place while the engine stumbled and the idle speed changed between 500 and 1200 RPM.

Like I said before this only occured when the engine was hot. An O2 sensor cured that.