i have a 1988 cherokee 4.0 automatic that has a major problem. when its cold it will fire up and run just fine but as soon as it reaches running temp (180), it boggs down and back fires when i give it ANY gas at all! it wont go above 15-20 mph when it does this. i've already replaced the fuel pressure regulator, fuel pump relay and cleaned out all the fuel lines and it has plenty of oil. it is definitely not a spark issue at all. before i replaces the pressure regulator, the valve in the old one wouldn't open so the fuel rail had too much pressure because the excess fuel couldn't go back into the tank. it no longer has that problem but is still running the exact same way (very badly at running temp) that it did before. im going to check the fuel pump today and the fuel filter but if that's not the problem i need help because it is my only car and i need it for this next week! please help!

 

check your cat when it starts to bog. see if she's glowing red.

 

Have you ever tested your fuel pressure with a gauge?

 

The cat isnt glowing red at all and is about normal temp, ive already taken the cat off to see if that helped and it did absolutly nothing so i put it back on. and i have not checked my fuel pressure with a gauge but i have opened the check valve on it and it seemed really low. and my fuel pump is only getting about 6 volts, should it be getting 12 volts? and i checked my fuel filter and its fine, keep the replies coming Thanks

 

There is a fuel pump ballast resistor located on the driver's side inner fender near the air cleaner. White, about 1 inch by 3 inches with a wire on each end. Should be 12 volts on one side with the engine running and about 10 volts on the other side. Check that and report back.

 

i just went out and checked it and when it was running fine it was 12 on one side and 10 on the other but then it acted up again and the ballast resistor read 12 on one side and between 8 and 9 on the other, i dont know if thats enough of a change to be whats causing the problem.

 

Bypass the resistor and connect the 2 wires together and see what happens then.

 

hmmm, i just went out and did that and it didnt help but usually when you unplug the resistor the car dies in a couple of seconds but i unplugged mine and left it unplugged and it kept on running, i even shut it off a couple of times and started it up and it still didnt die while running. what in the world wound cause that?

 

I wonder if someone screwed with your fuel pump wiring at some point. Might be worthwhile changing your fuel pump relay.

 

ive got another cherokee in my driveway that is my bro's and ive been, well i guess you could call it "stealing" parts off of his to fix mine. it ran great before i took his coil, crank positioning sensor, and i did take his relay to see if that helped and it didnt so i swapped that back. do you have any ideas what would cause the fuel pump to run with the ballast resistor unplugged? and is the pump supposed to be getting 12 or 6 volts. i have 12 volts at my resitor, 12 at my relay, but 6 at my pump....that seemes odd to me

 

Well, it's supposed to have 10V. Any cobbled wiring anywhere? If you put a jumper on the resistor, what voltage do you get at the pump?

 

well yea i have 12 on one side of resistor and anywere from 8-10 on the other. ill go check the jumper, and then swap my resistor with my brothers new one, and then ill see what im getting at my pump, ill be right back with the results.

 

Hurry up. I gotta take the wife to Lowe's.

 

jumper got 12 on both sides, and swapped the resistor with no luck. checked fuel pump, still only 6 but checked under rear seat for wire harness and got 10 volts on the pink and 6 on the brown using the ground for the pump as a ground. both pink and brown are getting 6 volts at the hrness under jeep but 6 on one and 10 on the other on the inside, im thinking io have a messed up wire?

 

its finally die once i unplugg the resistor but its taking up to 8 or 10 seconds when it should take about 3 or 4. hopfully not a big issue