Anyone have a wiring schematic for the fuel pump wiring on a 4.0 YJ circa 1991? I've got no power to the pump. I pulled the pump out and tested it and it does work, just not getting juice back there. I've swapped the fuel pump relay under the hood with a known good one with no luck. I'll have to double-check again tonight, but I believe I had voltage in the right places at the relay plug when the ign. switch was turned on. Where does it route from there and is there another fuse or relay I need to check?
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Help Support Hardline Crawlers :
4.0 YJ fuel pump issues
- Thread starter NotMatt
- Start date
Not Jobless
Mr Funbags
I haver the factory service manual at home, I can check when I get home.
I would think that there'd be a fuse in either the fuse panel or iin the power distribution box where the relay is.
I would think that there'd be a fuse in either the fuse panel or iin the power distribution box where the relay is.
crash2
-Oh no I picked a side-
Have you tried to jumper #30/#87 teminals to see if the pump runs? I assume the pump is ecm controlled and could very well be a failed ecm...
Sounds good guys. I'm not going to be able to work on it until tomorrow night most likely, so I will check that stuff and see what I can come up with. Crash your suggestion might be plausible, because I WAS using a torch near the ECU (cutting out the stock rusted in e-brake cable), so I might have gotten it a little too hot. Luckily I have a spare 4.0, 5-speed ECU boxed away somewhere if that's the case.
Update: it was the ECU. Swapped in my spare and the pump fired right up. Need to put the rig on the battery charger to see if it will actually run though, but I'm sure it will.
Moral of the story? Don't use a torch to remove the factory e-brake line on a YJ, even if it is rust-welded to the tub. :redneck: The old ECU didn't even look burnt/melted on the outside.
Moral of the story? Don't use a torch to remove the factory e-brake line on a YJ, even if it is rust-welded to the tub. :redneck: The old ECU didn't even look burnt/melted on the outside.
Ok... I lied, sort of. Looks like I have an intermittent grounding issue on the fuel pump. Made a jumper and grounded it directly to the body, starts and runs fine now.
Any reason why this can't be a "permanent" fix?
Any reason why this can't be a "permanent" fix?
junkyard jim
Well-Known Member
Doesn't it have a ground feedback through the oil pressure switch? No oil pressure equals no fuel pressure. (or maybe a rollover valve in the rig someplace?)
Not Jobless
Mr Funbags
Ok... I lied, sort of. Looks like I have an intermittent grounding issue on the fuel pump. Made a jumper and grounded it directly to the body, starts and runs fine now.
Any reason why this can't be a "permanent" fix?
Run it.
Not Jobless
Mr Funbags
As per the '91 factory service manual.
Colors at the fuel pump:
Black/yellow = Engine Ground
Tan/Black = Fuel Gauge
Orange/Black = Fuel pump relay
The fuel pump relay is wired through the ignition switch and fuse #9 (15A) under the dash and to complete the circuit attaches to pin 51 of the ECU
The relay itself gets power from F1 (30A) in the power distribution box under the hood.
Pin 51 on the ECU also controls the power relay for the heated O2 sensor.
I'd check the engine ground located on the block or head and the ground strap from the motor to sheet metal on the firewall. This ground is interconnected with the diagnositic port and the ECU, if it's bad then it will probably cause problems.
Colors at the fuel pump:
Black/yellow = Engine Ground
Tan/Black = Fuel Gauge
Orange/Black = Fuel pump relay
The fuel pump relay is wired through the ignition switch and fuse #9 (15A) under the dash and to complete the circuit attaches to pin 51 of the ECU
The relay itself gets power from F1 (30A) in the power distribution box under the hood.
Pin 51 on the ECU also controls the power relay for the heated O2 sensor.
I'd check the engine ground located on the block or head and the ground strap from the motor to sheet metal on the firewall. This ground is interconnected with the diagnositic port and the ECU, if it's bad then it will probably cause problems.
