DOBBSE.

2000 4.0 xj, I will be on the freeway runnin about 70 higher rpms around 2500-3000, once I get off and slow down to 45 speed around town I’ll have a nasty misfire until I pull over and shut the motor off. Once it starts again the misfire goes away and it runs smooth. Could this be either the crank or cam sensor? What else could this be?

That Jeep Guy XJMJ

Potentially o2 sensor? No check engine light? Does it clear back up immediately after restarting or just not as bad?

DOBBSE.

There is always a little stumble so there definitely is a problem. When I shunt it off and back on it still misfires just not as bad. I also sometimes have very low rpms at a complete stop.

tjwalker

Is check engine light on or have you seen it on? Very important question here....

If there is a code, you need to read it with a code reader or scan tool to give you information to help you diagnose it.

If you have a code or codes, post the exact codes here...not just a description. With OBD codes, the devil is definitely in the details.

DOBBSE.

The engine light will come on and stay on after I disconnect the battery and reset the computer. for a multiple/random misfire. It also blinks when it misfire is very badly.

tjwalker

Post the exact codes here for comment. Use the technology provided to you by your Jeep.

A flashing/blinking check engine light indicates a serious misfire, which if not resolved ASAP, will trash your catalytic converter by pumping unburned fuel into it.

DOBBSE.

P0171 bank one too lean. If I clear the code it will come on shortly after driving.
Could I switch the first set of 02 sensors around and see if that switches the code from bank one to two?

tjwalker

First thing to check if this was my XJ would be fuel pressure. Must be done with a gauge, can be rented inexpensively from many parts stores. For a 2000, you should have 49 psi, plus or minus 5. Also check to see if you have an exhaust manifold leak, quite common on these vehicles. Here is more from the FSM.
----------------------------------------------------------------------------------------------------------------
P0171-1/1 FUEL SYSTEM LEAN
POSSIBLE CAUSES

INTERMITTENT CONDITION
RESTRICTED FUEL SUPPLY LINE
FUEL PUMP INLET STRAINER PLUGGED
FUEL PUMP MODULE
O2 SENSOR
O2 SENSOR SIGNAL CIRCUIT SHORTED TO GROUND
O2 SENSOR HEATER OPERATION
TPS VOLTAGE GREATER THAN 0.92 VOLTS WITH THROTTLE CLOSED
TP SENSOR SWEEP
MAP SENSOR OPERATION
ECT SENSOR OPERATION
ENGINE MECHANICAL PROBLEM
FUEL FILTER/PRESSURE REGULATOR (HIGH)
PCM

5-Speed

^^^^^^ Exactly what he said. Sounds like fuel psi.

Desert Valley Berto

You cam and crank sensor is likely losing sync. When yoy turn it off and restart it reorients. Change the crank sensor. That should do the trick

cruiser54

If it was cam or crank sensor, why wouldn't there be a code for that?

Desert Valley Berto

On my rig it was hit and miss. Sometimes the code would come on Sometimes not. I would get a code for a shorted coil primary circuit or other codes but most of the time the code fir crank or cam sensor would not be listed. When finally bought an OE Mopar crank sensor it not only solved the problem but the jeep ran better.