hello,

I am new to this forum and hope that you guys can help.

I have a 1994 jeep xj 4.0 ho with auto trans 150000 miles and a resent new top end.

jeep starts and runs great until it warms up and then it will stumbel and backfire through the throttle body when taking off from a stop after that it runs good at speed.

I have replaced the fuel pump, o2 sensor, both temp sensors (but gage still doesnt work), air intake temp sensor, checked the throttle position sensor with meter and it seems to be working correctly, also replace the sensor on the transmission when the new head was put on. i have also checked the fuel pressure at the fuel rail and that seems fine as well.

i pulled the plugs and it looks like it is running lean.

only have this problem when jeep is warm?

Any idea?

Gravel

 

moved thread

 

The best thing to do is a search of 'backfire through intake' you'll find a lot of answers, a lot of other guys have had this issue, and the solutions range from bad ignition coil to the injector wires making contact with a heat shield. I would start with checking the MAP. Your motor running lean will cause this to happen....what was your fuel pressure at?

 

fuel pressure was about 31psi with vacume and 39 with out.

thanks for your suggestion ill check that out.

Gravel

 

Fuel pressure at idle should be 39psi on a '94. That would explain a lean running condition.