Fuel pump won't shut off

[JMO413]

Hi new to the site. I have a 88 Comanche 4.0 with a new problem as of today. The fuel pump will not shut off. If you pull the relay and I pulled all 4 in the passenger side inner fender area the fuel pump keeps running. The only way to get the fuel pump to shut off is to unhook the battery or unplug the fuel pump connector. Any thoughts would be greatly appreciated. 

[Ωhm]

1. Disconnect the BAL connector (ORN/BLK) at the starter relay.
2. Disconnect one of the two wires (both ORN/BLK) at the fuel pump ballast resistor.

Does either one of these turn off the fuel pump?
 

[JMO413]

The ballast resistor doesn't stop it tried that already. Going to try the starter relay now. Didn't think about that one. Thank you

 

[JMO413]

Pulled the connector off the starter relay. Fuel pump still runs.

[Ωhm]

Disconnect C157 (IP to CAB). Flat 6 pin connector located above/around the Parking Brake. This will divide the circuit in two.

[JMO413]

Did that. No fuel pump now

[Ωhm]

Disconnect C352 (single bullet connector) (ORN/BLK) located near the RH shock tower. Connect C157.

[JMO413]

Single wire barrel connector I want to call it? It's unplugged now. 

 

[JMO413]

[Ωhm]

With C157 connected, is pump on or is pump off? 

[JMO413]

Hooked up C157 runs again

[Ωhm]

Since we can't kill the fuel pump from under the hood and C157 kills the fuel pump, that leaves C100 (ENG to IP) (Bulkhead connector) left to check (separate). In other words, your short to voltage is between C157 and the battery. Put a voltmeter on the fuel pump wire (should read battery voltage) and trace the wire(s) back looking for wires touching each other. Best I can do sitting in my chair.

[JMO413]

I will start digging tomorrow thank you for your help. I found one other post about a Cherokee with a fuel pump that wouldn't shut off his final fix was an ECM does that make sense to you?

 

[Ωhm]

Not if you pulled out all the relays, it doesn't.

[JMO413]

Okay just checking only post I found about this issue. Yes I pulled all four relays,the ballast resistor, the starter relay leg, and disconnected C352 and the fuel pump runs. So if I understand you correctly I am getting voltage from another circuit shorted to the fuel pump wiring?

[Ωhm]

Yeah, lets hope someone else will chime in, but as of now, that the way I see it.

[JMO413]

Okay that's what I was afraid of. Thank you again!

[bad_idea]

That is weird.  Did you get the issue sorted?  I have never heard of a short to power.  Short to ground all the time, never short to power.  Then again, I am not a mechanic so I haven't seen ALOT of issues.  In situations like this I look to prior 'repairs' first.

 

I have a 79 Camaro that the dash lights came on with the ignition rather than the headlight switch when I bought it.  That one took me a while to figure it out.  Turned out the PO had installed an aftermarket radio.  Chevy hooked the dash lights circuit into the factory radio.  Radio lights came on with dash lights.  When the PO installed the radio he cut the plug off for the radio and twisted the IGN power wire with the dash light wire.  I separated the two wires and put a new fuse in the dash light circuit.  I drove the car for years with the dash light issue, was never a concern.  Only sorted the issue when I had the entire dash torn apart and decided to chase the issue.

 

It's interesting that your issue popped up suddenly.  Have you done any work to the jeep immediately prior to the issue?  Perhaps you disturbed something that was already a little off?  I am thinking perhaps PO rewired the fuel pump due to an issue and 'made it work'.  A fuse or relay failed and PO's jackleg circuit design went haywire.

[JMO413]

The PO had went around C157 with a toggle switch and ran power to the switch also. I had to go out of town for work and am going to try again today or tomorrow. The connection at C157 is nasty I think that's why he by passed it.

 

And yes I have done allot of work to this truck. Got rid of the PO horrible wiring job. He was a fan of scotch locks. I have done almost all of Cruisers updates. Headlight overlay, 4 hole injectors, cleaned and added grounds.

 

I finally had the truck running right and all the lights working. I also installed a 4.5 lift, changed all the fluids, got new tires and an alignment. Washed the truck really well for the first time in who nows how long. And then my fuel pump just kept running. 

[bad_idea]

Truck looks good at least.  I like the wheels.  Hope you get it sorted.  Keep us posted.

[JMO413]

Thank you. I will post if I figure anything out 

[Ωhm]

Ask if you can move this Post to "MJ Tech: Modification and Repairs". This will put more eyes on the subject.

[JMO413]

How do I do that?

[HOrnbrod]

[JMO413]

Thank you for moving this. Still tracing  wires today and still have not found a short. This is a weird one. I have spent the last two months fixing all the other issues.