Have a recently rebuild 97 XD motor. It idles great but backfires starting at 1500 rpm. Had a code for crank sensor so I have replaced :
crank sensor
cam shaft sensor
Rotor
coil
cap
new for plugs
checked fuel pressure(a steady 50psi)

yet still have a backfire at 1500 rpm and above.
What am I missing? Thanks

 

I had the same issue with my 99, a random misfire i tried lots of stuff then changed 02 sensor, cleaned TPS and worked good ever since, I really think it was the o2 sensor, it had no codes.

 

1. Did this engine run well AFTER the rebuild and the backfiring is a NEW symptom? Or has it been backfiring immediately after firing it up after the rebuild?

2. Is it backfiring through the intake or the exhaust? Knowing this can help in narrowing it down. Backfiring through the exhaust tends to be more of a rich issue. Backfiring through the intake tends to be more of a lean issue.

3. So if you scan the computer now, there are no codes?

The MAP sensor is directly involved with fuel/air ratio on your 4.0 engine. I'd test it and be sure that the vacuum line leading to it is pulling good vacuum. Also know that it is possible to have a fuel pump that provides the correct amount of pressure but not volume.

 

Backfire issue has been resolved. I replaced the entire distributor, and the Jeep runs great. Thanks for the response.

only issue now is I am still getting the p01391 code. But, Jeep runs great.