backfiring after warms up

[sernas]

I have a 97 TJ 4.0 auto and i just put new rod bearings and main bearings and got the head rebuilt it starts up right away no weird noises or anything runs good at any rpm that is until it warms up then at about 1750 rpm it starts backfiring and feels like its missing wont go anywhere until i rev it passed 1750 rpm or lower rpm any ideas of what it can be im not getting any misfire codes or any other ones???

[Muad'Dib]

What shape is your ignition system? Plugs, wires, cap, rotor coil etc... Your running rich / having incomplete combustion if your backfiring out the exhaust.

What shape is the cat in also?

[sernas]

Coil is fairly new no cracks visible ignition wires no tears or anything brand new autolite 985 gapped at .35 i also run no cat everything was fine before new engine now engine seems to starve for fuel only at about 1700 rpm up to around 2000 and then clears up

[Muad'Dib]

Some "experts" say that not having a cat can cause a backfire in the exhaust...

You say that the engine is starving for fuel, i take it then that the backfire that you are experiencing is in the intake and not the exhaust??

Maybe someone else can chime in here... or have you tried searching NAXJA? There are more guys there that are readily available to answer non-stroker questions.

[SilverXJ]

Have you checked your preload on the lifters?

[yuppiexj]

If backfires at that RPM range with light/ no load on the engine I would say your distributor needs to be re-indexed.

http://www.angelfire.com/my/fan/dist_index.html

I had a 1989 XJ that did it from the factory. my 1994 did the same thing after I swapped in a new engine.
The best about this is that it's a FREE fix

[sernas]

its coming out of the exhaust not intake and if it was lifter preload or dist. off wouldnt the problem occur at all times? and i'll check out xj forum it only does it after driving it for like five or ten minutes