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Question -
97 GMC SUBURBAN C1500 350 Car quit on road, discovered fuel pump wasn't working. Direct connection to pump caused pump to run. ALDL fuel pump check had no action. Fuel pump fuse is good. Partially lifted fuel pump relay out of it's socket in the relay center and ran a direct battery line to the 87a(gray)post, fuel pump ran. Oil pressure switch test on ALDL OK (no light) What next? Thank you for your time, Joe
Answer -
Possible faulty fuel pump relay. Look around at the other relays and I believe that the A/C relay is an IDENTICAL style relay so you can SWAP them to see if the fuel pump now runs.
Here is how the system works:
1. ECM commands fuel pump relay to engage for TWO seconds of which runs the fuel pump to pressurize the fuel system when you turn ON the ignition to start the engine.
2. Once the engine starts the fuel pump relay is BY-PASSED and the fuel pump is fed battery voltage DIRECTLY from the ECM.
Did you check and physically remove and test the FUEL PUMP FUSE ?.
What mechanical work or ANY kind of work has been performed on the vehicle recently ?. As most problems that occur after a recent repair was made can be traced back to the area of where the repair was made as a wire connection came loose, Look around in the area where work was performed..
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I do hear the 2 second fuel pump pressurize then nothing.
The fuel pump relay has 5 pins and the AC has 4. The AC and ignition relay are the same. I did switch the AC and ignition relays to try to get my AC to work. Ignition worked with either one and the AC did not. A direct line to the AC makes it run. A direct line to the fuel pump makes it run. I was driving when the fuel pump quit. Is there something wrong with my PCM? I did physically remove and test FUEL PUMP FUSE. I can't find anything wrong with the FUEL PUMP RELAY but when I run a direct line to the center post(87a fuel pump prime connector) I hear the pump running. could there still be something wrong with the RELAY?
AnswerYou stated: "I do hear the 2 second fuel pump pressurize then nothing. THIS IS NORMAL and is OK.
A REVISION to prior # 2 previously stated:
2. Once the engine starts the fuel pump relay is BY-PASSED and the fuel pump is fed battery voltage DIRECTLY from the ECM to the OIL PRESSURE SWITCH and then back to the fuel pump. You could very easily have a faulty oil pressure switch and or faulty connection at the oil pressure switch plug.
See if your oil pressure switch has 3 electrical connectors attached to it. If it DOES, replace it and check the inside of the plug to be sure the connections are clean and tight.
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