Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
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ok you have one of to things going on either there is continous power to the control side of the relay or there is continous power to the high side of the relay that send's power to the pump,first remove the f pump relay and see if that kills it,if so replace it with a different relay,you might have another relay like it in the box like the headlight or ac (they should have the same part number),you might have damaged wiring from a fire,of mice,ect is the fuel pump the only thing that stays on?
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ok you might have more than one thing going on.the fuel pump running continously may be a ecu (computer)problem,the pump should cycle for 3 seconds after you turn the key on the first time then it will stop running untill you crank the engine you may want to check the fuel pressure by connecting a guage to the fuel test port on the fuel rail if you have one,or have some one crank the engine while you listen inside the fuel tank thru the filler neck to see if you hear running constantly
It's the Oil Pressure Sending Unit (OPSU). Where it's located on your engine I don't know - but that's the culprit.
Electric fuel pump gets power from the relay ONLY FOR PRIMING the pump. The continuous power for the fuel pump comes through a connection from the battery directly through the OPSU and directly to the fuel pump. A bad OPSU can cause the pump to run no matter what until the battery is disconnected or dead (Gee - wonder how I know this? LOL).
This is a safety feature built in - no oil pressure = no fuel getting pumped out. But since there is a direct connection between battery and fuel pump through the OPSU - the OPSU can go bad in a way in which it "thinks" it's getting oil pressure when it's not - thus supplying power constantly to the pump. Find and replace the OPSU.
there ya go,I have seen that style circuit on blazer's before,gm must run that on alot of models,sorry did not have schematic sitting In front of me ,cnewbie is the man
