For anyone that THINKS they know these setups, why don't you pull out the GM service manual, and read up on prolonged cranking. What's one of the causes? Failed fuel pump relay. Oil pressure switch closes at ~4PSI, so if the relay fails, it will take more cranking (thus, starter generating oil pressure, which takes time) for the switch to close and the pump to run, but it WILL start if the switch is working right and pressure gets high enough.
Now, I've *heard* people say that their setups don't run if the relay is disconnected, and I won't call them liars, but that is not how they are wired up...the pump hot wire from the relay is spliced into the oil pressure switch wire, which is HOT when the switch closes...thus, if the switch closes, there will be 12V on the pump 12V "out" on the relay connector. You could easily check continuity with both unplugged, between the oil pressure switch and the relay connector.
IIRC (and this is off the top of my head, think I've dealt with this before? lol) the oil pressure switch will have one wire with 12V key on, engine off. The OTHER wire on that connector is the one that will have continuity with the pump 12V wire, and one of the terminals on the relay connector.
Note that there is a red wire hanging off the fuel pump relay, connected to nothing? Put 12V to that and the pump should run. Bypasses relay. Again, off the top of my head, there should be continuity between that red wire, and the non-ignition 12V wire on the oil pressure switch.
Think about it...the only way the pressure switch would be a safety would be IF the relay has failed and is not powering the pump. Since this truck dies if the relay is disconnected, and the PCM controls the relay (it does) then that means the oil pressure switch in a properly working setup could never kill the relay, since it's not wired to the PCM in any manner...it would have to be able to tell the PCM there is no oil pressure, and since neither of the oil pressure switch wires go to or from the PCM, it's obviously not capable of killing the engine, again with a proper running setup.
Additionally, if it WERE a safety feature, assuming this setup is idling at more than 4PSI, why would the engine die if the relay is disconnected? Certainly no point to it if it dies above or below 4PSI. In fact, that would be a pretty pointless device no matter what it would be for.
Edit: Thumb down? LOL, I like how someone even bothered to try and provide different info.
If you unplug the fuel pump relay on a GM vehicle while the engine is running, the pump should still run. The oil pressure sensor is the backup switch to the fuel pump to provide power in case the relay fails. But it doesn't work the other way. The oil pressure sensor is designed to kill the engine if oil pressure is too low or the computer stops receiving a signal. That's the emergency shut off.
It won't run without the the relay. The oil pressure sends a signal to the relay to close the contacts to make the pump run. You can try swapping the air conditioner relay with the fuel pump relay. They are the same part numbers. If the pump works, get a new relay.
It shuts off right when I disconnect the relay even with the new oil pressure sensor, where can I find a wiring diagram that tells volts and reference signals?
Stop listening to people who tell you stuff like that. Get a service manual and read it. I have no idea what you're actually trying to do to your car, but it sounds like you're just determined to ruin it.
On a 1990 k1500 I was told that you should be able to disconnect fuel pump relay when it is running to stay running , I already installed a new oil pressure sensor, it stalls when you unplug it , can any one give me more advice or have specs on oil ps wires so I can test them
