I had to replace the original engine; i found one in a running and driving 1989 XJ, after i got the engine out i noticed the block casting was 10-12-96... not sure if that means anything. I put the engine in my 90 XJ, everything fit right so i re-used my distributor and fuel rail, it started & idled perfectly- when i gave it gas it started backfiring through the intake and wouldnt rev... I replaced the fuel pump and filters before the swap, and i have checked all the wiring & connections, & vacuum lines. I went and got the fuel rail, injectors, distributor, and computer, from the jeep that i took the motor from, still does the same thing... start and idle perfect, wont rev, backfires through the intake, it gets real hot real fast... dont know if that means anything... Please HELP!!!! any ideas or info would be greatly appreciated!!!