Expert: autohelp - 11/18/2009

Question
QUESTION: My 2000 escalade has no power at the fuel pump plug in.  Truck quit running but will crank strong.  Tested fuel pressure at valve on fuel rail and had zero pressure.  Replaced fuel filter and fuel pump.  Turning key to on while testing and cranking and i have no power at fuel pump plug in.  I replaced fuel pump relay fuse and ECM B fuse.  Using power tester I have power to ECM and relay fuse in block while key is off.  What else could be my problem.

ANSWER: Here is a test procedure to see if the fuel pump works when your problem occurs.

1. Remove the gas cap.

2. Listening very carefully with your head out the door and getting as close to the ground and listening at the gas tank.

3. Turn the ignition switch to the ON position ONLY, Do NOT try and start the engine. You should be able to hear the electric fuel pump motor run for only 2 seconds and then it will stop.

4. If you can hear it run for the 2 seconds and then stop, You do NOT have a fuel pump problem.

   (a) If you do NOT hear the fuel pump run for the 2 seconds and stop then the fuel pump is faulty and requires replacement.

5. If the fuel pump is OK, You need to check for spark to the spark plugs.

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QUESTION: Fuel pump has already been replaced.  No power at plug for pump.  Relay and ecmb fuse already replaced.  Unlikely that both powered wires on pump pigtail broke at the same time. Some other safety shutoff or power source?

Answer
When you FIRST turn ON the ignition switch battery voltage is provided by the computer to the fuel pump relay for only 2 seconds to prime the system with fuel pressure.

Once the engine starts and the oil pressure builds up, The relay is NOT used and the voltage is provided from the computer thru the oil pressure switch to the fuel pump.