i have a and it has some trouble starting but when it starts it idles fine than if it is put in gear in back fires than dies??? simple fix?

Sounds like your timing is too far advanced.

when was last complete tune up ?

I have a beater 84 xj with the 2.8. Id agree with checking the timeing. Alot of people think that motor is junk mines been very reliable. Seen 7800 RPM a few times.

there not a bad motor at all just gotta take care of them .