1. Verify Power at the Pump: You mentioned power at the *plug*, but that doesn't guarantee power *at the pump itself*.
* Directly test the pump wires: Disconnect the fuel pump wiring harness. Use a multimeter to check for voltage at the wires going to the pump when the ignition is ON (but *not* cranking the engine). You should have battery voltage (12V) present. If you don't, the problem lies in the wiring between the plug and the pump.
* Ground connection: Check the ground wire connection at the fuel pump. A poor ground can prevent the pump from operating even with power. Clean the ground connection and ensure a solid connection to bare metal.
2. Fuel Pump Relay: Even if you've replaced or tested the relay, there's a possibility of a faulty relay or a problem with its circuitry:
* Relay Swapping: Try swapping the fuel pump relay with another relay of the same amperage rating (check your owner's manual or online resources for the correct relay). This helps eliminate a faulty relay as the culprit. Don't just test it in its socket; physically swap it with a known good one.
* Relay Circuitry: Trace the relay's circuit from the fuse box. Check the fuse associated with the fuel pump. Ensure there are no broken wires or loose connections in the circuit.
3. Inertia Switch: The 1997 Tahoe likely has an inertia switch (a safety device that cuts power to the fuel pump in a collision). Locate the inertia switch (usually under the dash or in the engine compartment) and reset it by pressing the button.
4. Check the Fuel Pump (if accessible):
* Direct Power Test (CAREFULLY!): If you can safely access the fuel pump without risk (consider disconnecting the battery), you can temporarily apply 12V directly to the pump using jumper cables. Exercise extreme caution! Gasoline is flammable, and sparking near it can cause a fire. Only do this if you are extremely comfortable working with automotive electricity and fuel systems. If the pump works with direct power, the problem is in the wiring or relay circuit.
* Listen for the Prime: When you turn the ignition key to "ON" (but not cranking), you should hear the fuel pump briefly prime (run for a few seconds). If you don't hear it, the pump is likely faulty or has a wiring issue.
5. PCM/ECM: In rare cases, the Powertrain Control Module (PCM) or Engine Control Module (ECM) can cause the fuel pump to fail. This is less likely, but should be considered if all other checks are fine. A scan tool would be needed to diagnose PCM/ECM issues.
Important Safety Notes:
* Disconnect the negative battery cable before working on any electrical components in your vehicle.
* Work in a well-ventilated area when dealing with the fuel system. Gasoline fumes are dangerous.
* Never work near an open flame while working on the fuel system.
* If you are not comfortable working with automotive electrical systems, take your vehicle to a qualified mechanic.
By systematically checking these points, you should be able to pinpoint the reason why your fuel pump isn't working. Remember to replace any faulty components or repair any damaged wiring.
