Fuel pump running with key off (Solved!)

[YukonGTmaster]

I parked in the garage after a rainy drive on the highway. When I shut the truck off and pulled out the key, I could hear the fuel pump running continuously. I disconnected the negative battery terminal, and have not touched it since. Any thoughts where to troubleshoot first?

 

[Fless]

Swap the fuel pump relay with another like relay, to see if the relay is stuck?

 

[YukonGTmaster]

I reconnected the battery and the fuel pump started running right away. I removed the fuel pump relay, and the pump kept on running. No keys in the ignition. I removed the connector at the oil pressure switch and……the pump stopped.

 

[ivin74]

The key switch might be getting stuck. Try messing with it and see if makes any difference.

 

[YukonGTmaster]

It turned out to be the oil pressure switch in behind the distributor. I replaced this switch first back in March. I replaced it, and when the engine was warm, the pressure read so low that the “Check Engine” (low oil pressure) light would illuminate. Rock Auto sent me a warranty switch. Looks like it shorted inside, and ran my Fuel Pump direct battery, with the ignition off. Luckily I didn’t throw out the old low pressure switch. Hopefully it lasts until I can pick up an OEM switch from the GM dealer Tuesday.

Big thanks again to @east302 for recommending the oil pressure switch socket way back in March. Without that socket, I would of had to pull my distributor about 6 times because of these cheap switches.

 

[YukonGTmaster]

Oil pressure switch replaced with OEM part. Picture of oil pressure Cold at idle, and Warm at idle.

 

[OR VietVet]

Another PITA solved.

 

[exp500]

My question is why oil press switch hot with key off. Not having looked at diagram.

 

[YukonGTmaster]

My question is why oil press switch hot with key off. Not having looked at diagram.

Apparently there is a circuit in the oil pressure switch, that will cut power to the fuel pump, in the event of total loss of engine oil pressure. I am thinking this may be a safety precaution in case of a rollover crash? It would seem that this circuit shorted in my cheap aftermarket oil pressure switch, allowing my fuel pump to run direct from battery even when the key was off.

Does anyone have a wiring diagram they could chime in with?

 

[exp500]

I understand rollover switch use, but I believe it should be key on hot only. Maybe I'll look later if I think about it again. Thanx for the reply though.

 

[YukonGTmaster]

I pinned out the two contacts parallel to each other on the bad pressure switch, and the circuit was closed. On the new switch those contacts had no continuity.

 

[exp500]

I looked and I'm sorta surprised. Hot from fuse. Learned something again from the board!