97 XJ Fuel pump issues

J

Jeep Sarge

NAXJA Forum User
Location
Mississippi
Hello I am new to the Forum but not new to jeeps here is the rollup as follows


Currently 1954 M38A1 , 00 WJ , 97 XJ , 99 WJ
:( *** Previous *** 91 YJ, 92 YJ, 93 YJ, 98 TJ, 84 FSJ, 77 CJ5, 90 YJ, 03 TJ, 87 MJ, 97 TJ, 88 XJ, 99 WJ, 97 TJ, 95 YJ, 97 TJ, 97 TJ

Alright now for the issue! I have a 1997 Cherokee Sport 4x4 runs and drives good, but when i turn the A/C on then it kills the power to the fuel pump and dies. soooo With A/C on no power to the fuel pump, weird thing is if you apply the brake pedal the fuel pump will run, brakes off no fuel pump, A/C off Fuel pump??

I am at a brick wall, i have checked every fuse, swapped out all relays, and inspected all wires, even swapped out the PCM. I have tried reading and reading topic after topic and no luck, I have a HAYNES manual but the wiring diagram in it sucks and i havent ran across a FSM on this vehicle. any help suggestions or time would be greatly appreciated.
 
Jeep Sarge said:
Hello I am new to the Forum but not new to jeeps here is the rollup as follows


Currently 1954 M38A1 , 00 WJ , 97 XJ , 99 WJ
:( *** Previous *** 91 YJ, 92 YJ, 93 YJ, 98 TJ, 84 FSJ, 77 CJ5, 90 YJ, 03 TJ, 87 MJ, 97 TJ, 88 XJ, 99 WJ, 97 TJ, 95 YJ, 97 TJ, 97 TJ

Alright now for the issue! I have a 1997 Cherokee Sport 4x4 runs and drives good, but when i turn the A/C on then it kills the power to the fuel pump and dies. soooo With A/C on no power to the fuel pump, weird thing is if you apply the brake pedal the fuel pump will run, brakes off no fuel pump, A/C off Fuel pump??

I am at a brick wall, i have checked every fuse, swapped out all relays, and inspected all wires, even swapped out the PCM. I have tried reading and reading topic after topic and no luck, I have a HAYNES manual but the wiring diagram in it sucks and i havent ran across a FSM on this vehicle. any help suggestions or time would be greatly appreciated.
Click to expand...

How do you know the power is removed from the fuel pump when AC is turned on?

Are you saying the engine dies when AC s turned on, or the fuel pump dies?
 
When the jeep is running and I turn on the a/c or heat then the engine dies, I checked and there is no power to the fuel pump when this happens. So if I turn the a/c on before cranking the jeep will not start till I cut it off and power returns to the fuel pump
 
Jeep Sarge said:
When the jeep is running and I turn on the a/c or heat then the engine dies, I checked and there is no power to the fuel pump when this happens. So if I turn the a/c on before cranking the jeep will not start till I cut it off and power returns to the fuel pump
Click to expand...

Of course you know the fuel pump will not run unless the engine is running...right? If the engine is not running there will be no power to the fuel pump; only a momentary pulse when the key is turned to RUN before starting. The fuel pump relay control coil is powered from the START-RUN bus...the engine must be STARTED and RUNing for the control coil to be powered.

Do you have a voltmeter on your instrument cluster? It's not that accurate but it will give a ballpark voltage. The PCM requires 9 volts minimum to operate. If your voltmeter shows a drop in voltage to, or below, 9 volts the PCM will terminate the ASD and fuel pump, amongst other circuits, and the engine will shut down. Say Good Night Gracie...

Check your voltmeter while cranking and when running when the AC is requsted. If the voltage drops way off it may be the alternator/battery is not keeping up with the bus demands.

If you see a voltage drop with the AC requested, pull the AC fan relay in the PDC and try it again. The fan is fused for 40 amps but only draws about 1/3 of that. If the engine stays alive with the fan relay removed you can think about the alternator being shot, and/or the battery being shot. Remove both and take them to a store (O'reilly, Advance, etc.) and have them checked.

If there is no change with the fan relay removed, and the voltmeter doesn't drop off to below 9 volts, the only thing in common with the HVAC system and the fuel pump is both are chassis grounded, albeit at different locations. The HVAC system is grounded at G108, under the dash, and the fuel pump behind the spare tire mount in the cargo bay. They are powered from totally seperate fused power sources.

If the alternator and battery bench check okay, try refreshing the ground at the right fender-this is the direct ground path from the chassis to the battery. The negative battery cable has two cables, one to the engine block below the ignition coil and one short one that goes to the right inner fender. Detach the fender ground cable and make sure it's clean and corrosion free then reconnect.

Report back please. :compwork:
 
Good on alternator and battery for sure, to throw another kink in the ordeal if the jeep is running and you have your foot on the brake the ac will work properly and stay running, when you release the brake, engine died because fuel pump shuts off and ac stays on.
 
Jeep Sarge said:
Good on alternator and battery for sure, to throw another kink in the ordeal if the jeep is running and you have your foot on the brake the ac will work properly and stay running, when you release the brake, engine died because fuel pump shuts off and ac stays on.
Click to expand...

Brake pedal envolvement put aside for now...

I still can't figure out how you know the fuel pump shuts off.

Early on you said "When the jeep is running and I turn on the a/c or heat then the engine dies, I checked and there is no power to the fuel pump when this happens."

Then I said "Of course you know the fuel pump will not run unless the engine is running...right? If the engine is not running there will be no power to the fuel pump; only a momentary pulse when the key is turned to RUN before starting. The fuel pump relay control coil is powered from the START-RUN bus...the engine must be STARTED and RUNing for the control coil to be powered."

Under what conditions, and how, are you determining there is no power to the fuel pump?

When the engine dies, does it die suddenly like turning the ignition off?
 
Nope engine is starved of gas then does. Alright to clarify the verification I have put a test light on fuel pump, turned the ignition to on and don't get the 3 second pulse at the fuel pump, key still on run Turn the ac off and then I get the 3 second hot light.
 
I guess it's time to isolate circuits.

Try pulling the 40 amp fuse in the PDC for the HVAC blower and see if the engine still stops with AC selected. If the engine runs okay with this fuse removed the HVAC blower motor/resistor block ciruit is defective. If the engine still stops, remove the 15 amp blower motor relay control fuse from the JB and see what happens. These two fuses are the only power sources in the HVAC system.

1997-1999XJPDCannotatedrev02_21_13.jpg


97-99XJJBHVACBlowerRelay10.jpg
 
I have fought a lot of weird electrical problems on 97+ xj's that end up being the fuel pump shorting out/causeing all kinds of electical problems. Now everyone that I have encountered would loose all dash gauges/hard start problems and that usually key's me in..
 
Alright can somebody explain the fuel pump issues that are related to the gauges I noticed today while driving I know that I have fuel in it but my fuel gauge went below E and stayed there for a while and then eventually came back up to the right location is this some of the issues that others have been having with wireing?
 
Just dealt with a similar issue with my buds 97. The plastic connector was busted and was causing a short. The rear leafs are junk it every time it would bottom out it would crush the plug. Water eventually got in there and he would get weird fluctuations in the fuel gauge then it would die. Worth a shot to check that plug out. We ended up cutting the plug out and soldering/shrink tube it for now till I can get to a junkyard to cut out a new plug.
 
Any relief with this issue? I am having the same issue with my 99 sport. Everything is kosher with my foot in the brake. Let off the brake gauges all drop and motor dies. Acts just like turning off the ignition.if I leave the ac running the vehicle will not restart. Cycling the key the fuel pump never turns on.turn off the AC cycle the key and it will fire right up. I'm so confused.
 
No good idea, but I have to wonder if this might be some sort of ground problem wherein the proper ground is compromised, but an alternate ground circuit is being found through the brake lights.

That is just a guess.

Seeing as how more than one person has encountered this problem it would be nice to document the solution once you find it.
 
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