HELP!!! My XJ is dying!!

For starters: I have an 88 XJ with a 4.0 I6.

OK. here is the problem. when i am driving at anything above idle, it is bogging down terribly and backfiring through the throttle body. i can not give the engine gas or it starts to bog down and stumble and pop. when i have it parked, or in neutral i can rev the engine as high as i want with no problem.

here is everything that has been replaced recently: plugs, wires, cap, rotor, nearly every sensor. (tps, iac, o2, map) new egr valve, cleaned the throttle body, and new fuel filter. i also replaced all of my vacuum lines.

after some suggestions, i had the battery and alternator tested. they are fine. someone suggested the catalytic converter, looks ok to me.

i did a fuel pressure test and only came up with about 23 psi. i think thats too low and maybe it is my problem. i want to change the fuel pressure regulator, and have a look at the fuel pump.

this is where i stand right now. any help is appreciated.

That's a tough one. What were the event leading up to your problems. Was any work done before it started? Was is gradual or all at once?
1. Maybe bad gas? Try a good quality fuel sys cleaner/water remover.
2. If you have adj timing, have timing checked.
3. Is it doing it in reverse too? If so, are brakes properly adjusted?
4. Is the engine making any noises, clicking or knocking?
5. Check air intake, air filter clean?

I have gone through all of those things except timing which i hope to get to this weekend.

If you have a cole muffler in your area they will flow test your converter for free.... that would bog it down but not so sure about the popping noise...

A bad cam shaft would give you a popping noise and bog it down... but it would do it in neutral also... run a compression test


Good luck... Let us know what you find

well, because of my low fuel pressure, i thought i would replace the fuel pump. i found that the pump had a broken return line and the filter sock was gone and pump clogged. i put in a new pump, redid the pressure test and it was at the right pressure. after driving it a round today, i cant believe the difference. my xj is as good as it has ever been! i am astonished that the fuel pump caused all of these problems.

Hey guys, The timing is controled by the computer from the Crank position sensor. This is part of why it takes the older Cherokees longer to start up. The computer was only told where #1 plug is from the CPS. So it would have to turn over a complete revolution before it would start firing the plugs. The newer ones put off a fake kinda fire to get it going till it knows where number 1 is located. The timing is not servicable unless you want to cut the tab on the distributor so that you could rotate it. The only problem with this is that it will only affect the timing of the Fuel Injectors.