1. Check the Obvious:
* Listen for the pump: Turn the key to the "ON" position (don't crank the engine). You should hear a brief whirring sound from the fuel pump (usually near the fuel tank). This confirms the pump is getting power and attempting to prime. If you don't hear it, proceed to the next steps.
* Check the fuel level: A simple, but often overlooked, issue. An empty tank will obviously prevent the engine from running, even if the pump works.
* Look for obvious leaks: Inspect the fuel lines, tank, and pump for any visible leaks. Fuel leaks are serious and require immediate attention.
2. Test Fuel Pressure:
This is the most crucial step. You'll need a fuel pressure gauge that's compatible with your vehicle's fuel system. Consult your owner's manual or a repair manual for the correct specification.
* Locate the fuel pressure test port: This is usually on the fuel rail.
* Connect the gauge: Carefully connect the gauge to the test port.
* Turn the key to "ON": The gauge should show the fuel pressure. The exact pressure should be specified in your repair manual, but it's typically around 35-45 PSI for a 1991 Chevy truck.
* Check pressure with the engine running: Start the engine (if it starts). The pressure should remain steady. A fluctuating or low pressure indicates a problem with the fuel pump, fuel filter, pressure regulator, or other parts of the fuel delivery system.
3. Check Power and Ground to the Fuel Pump:
If the fuel pressure is low or nonexistent, you need to investigate the electrical supply to the pump.
* Locate the fuel pump relay: This is usually found in the underhood fuse box. Consult your owner's manual for its location.
* Test the relay: Swap the fuel pump relay with another relay of the same amperage (make sure to label which relay goes where). If the truck starts, the relay was likely faulty. If this doesn't solve the problem, continue to the next step.
* Test the fuel pump power and ground wires: Disconnect the fuel pump electrical connector. With a multimeter, test for power (12V) at the connector while someone turns the key to the "ON" position. Also, test for a good ground. Lack of power or ground suggests wiring issues.
4. Consider Other Possibilities:
* Clogged fuel filter: A clogged fuel filter will restrict fuel flow, leading to low pressure. Replacing it is relatively inexpensive and easy.
* Faulty fuel pressure regulator: This component regulates fuel pressure. A faulty regulator can cause low pressure or pressure that fluctuates.
* Fuel tank issues: A problem inside the fuel tank, like debris or a collapsed fuel tank, can hinder fuel delivery.
* Pick-up tube: The tube that draws fuel from the bottom of the tank could be blocked or damaged.
Important Notes:
* Safety: Always disconnect the negative battery cable before working on the fuel system. Fuel is flammable, and precautions should be taken to avoid sparks or open flames.
* Repair Manual: A repair manual specific to your 1991 Chevy truck will provide detailed diagrams, specifications, and troubleshooting procedures.
* Professional Help: If you're not comfortable working on your vehicle's fuel system, consult a qualified mechanic.
This detailed approach should help diagnose the problem. Remember to replace parts with OEM or high-quality aftermarket parts to ensure longevity.
