1996 Yukon fuel pump is running after vehicle is turned off.

[YukonDude]

I turn off the truck and the pump still runs. I have to unplug my battery cable to stop it because even when I pull the fuel pump relay it still runs. What's up with that? Is my pump bad? I replaced it like 2 months ago.

Another issue I have is my oil pressure gauge is not working, the needle is just sitting way past 80. Could it be a bad sensor or is it worse?

 

[JKmotorsports]

If your pump continues to run even with the relay removed, then you might have a short somewhere after the relay on the +12v wire from another +12v source, which is rare. Are you removing the right relay?

 

[YukonDude]

Yeah I definitely removed the right relay, and I got so pissed off I took the tank down to check the wiring harness to the fuel pump. The ground pin in the connector seemed to be pushed inside. So I thought I found the problem, but I bought a new fuel pump and a new wiring harness, replaced both and guess what? The pump is still running with the truck off and key out of ignition and even with the relay unplugged.

I'm about to flip, this is driving me insane! I have a couple questions. Could it be a bad ECM/computer? Could this be also related to my oil pressure gauge not functioning? Because these 2 things both happened after I changed my transmission.

 

[95TwinTT]

I’m going to guess that the wiring got pinched and shorted, that connects to the oil pressure sending switch.

They have some of the fuel pump circuitry going through the oil pressure sending switch to guard against running the engine without oil pressure.

Having just wrestled with the tranny makes this a more likely scenario than the sending unit going crazy……..

That sending unit is at the top of the block, behind the intake manifold. Look closely at the wires back there that could have gotten in the way, or may be pinched between the engine and tranny.


That would also explain your oil pressure gauge on the dash. They are, after all, just volt meters with various dampers on them. Voltage on the wrong wire would take your oil pressure gauge to the max as well as provide voltage to the fuel pump…..

 

[steamroller]

If mine is running and I pull the relay it continues to run, I've seen it mentioned that it's in case the fuel pump relay fails power is routed through the sending unit as long as you have oil pressure. But if I pull the relay then try to start it, it will not start. Sounds crazy but all I can say is try it for yourself. Already been said but if there is no oil pressure then it won't run or start either

http://www.fullsizechevy.com/showth...wners-Does-your-truck-run-w-o-Fuel-Pump-Relay

http://www.blazerforum.com/forum/showthread.php?t=35109



So it's most likely the sending unit or a pinched wire causing your problems. If the gauge is pegged it thinks you still have oil pressure so power is being sent to the fuel pump. My theory anyway

 

[95TwinTT]

The oil pressure sending unit is a variable resistive device for oil pressure, not an on/off switch. The second component of it is, however a switch to + 12 volts.

If the oil pressure gauge is pegged, it means it is seeing a full 12 volts, which would be impossible under normal circumstances. The wires must be crossed to enable this to happen.

The clue is a transmission as just been R and R’d and the wires in question, hang at the top of the engine block, in harms way during that procedure.

I would put all my effort into verifying that those wires are not damaged..

 

[retorq]

I've had the wiring harness pinches between the tranny and engine on my Blazer, it was a pain in the ass.

 

[YukonDude]

Thanks for all your help guys but I think I will have to let a knowledgeable mechanic tackle this because I also had an abs light pop on today...what more do I need? I love the damn truck, I used to own a bronco before this one and believe me riding the Yukon is 100 times better, but I wish the problems were less complicated and easier to figure out.

 

[95TwinTT]

We're not talking about anything other than taking a flashlight and looking at the wiring harness in the back of the engine.

The one that plugs into the oil pressure sensor. See if it is crushed or pinched between the bell housing and the engine.

If it has been roughed up, there should be evidence. At least you can eliminate that from the equation........... Just sayin...........

 

[steamroller]

The oil pressure sending unit is a variable resistive device for oil pressure, not an on/off switch.

Never said it was lol. I just stated that pulling the fuel pump relay won't kill power to the pump if the engine is running. Backs up what your saying about 12 volts being there in the wiring and the probability of the wires being pinched.