1. Verify the Fuel Pump Hum:
* Location: The fuel pump is usually located in the fuel tank. You may hear a faint hum from inside the cab, particularly with the key in the "on" position (not cranking). If you don't hear anything, the pump might be completely failed.
* Duration: The hum should last only a few seconds with the key in the "on" position before it shuts off. If it hums continuously while cranking, that could indicate a problem with the pump or its relay.
2. Fuel Pressure Test:
This is crucial. You'll need a fuel pressure gauge that's compatible with your vehicle's fuel system. The gauge is typically connected to the fuel rail (a metal bar on the intake manifold that distributes fuel to the injectors). The pressure should be within the specifications listed in your owner's manual (typically between 40-60 PSI, but check your manual). Low or no pressure confirms a fuel delivery issue.
3. Fuel Pump Relay:
* Location: Check your owner's manual for the location of the fuel pump relay. It's usually in the underhood fuse box.
* Test: Swap the fuel pump relay with a relay of the same amperage rating from a different circuit (make sure you don't swap it with a crucial relay). If the truck starts, the old relay was bad.
4. Crankshaft Position Sensor (CKP Sensor):
A faulty CKP sensor won't allow the engine to get the signal it needs to fire. If the truck is turning over but not starting, this is a common problem. This sensor provides crucial information to the engine control module (ECM) for timing.
5. Cam Position Sensor (CMP Sensor):
Similar to the CKP sensor, a faulty CMP sensor will prevent the engine from firing. It tells the ECM about the camshaft's position.
6. Ignition System:
* Spark Plugs and Wires: Check the spark plugs for wear, fouling, or damage. Inspect the ignition wires for cracks or damage.
* Ignition Coil: A faulty ignition coil can prevent spark to one or more cylinders. A coil test can determine its condition.
* Distributor (if applicable): Older vehicles have distributors, but your 2002 Sierra probably doesn't.
7. Fuel Injectors:
While less likely if you hear the fuel pump, faulty injectors could prevent fuel from being sprayed into the cylinders. A fuel injector test might be necessary, but this is more advanced diagnostics.
Troubleshooting Steps:
1. Start with the easiest: Check the fuel pump relay first (step 3). It's a quick and cheap fix if that's the issue.
2. Fuel Pressure Test (step 2): This is the most important step to determine if the problem is fuel-related.
3. Sensors (steps 4 & 5): If fuel pressure is good, move on to checking the CKP and CMP sensors. These are relatively inexpensive and easy to replace.
4. Ignition System (step 6): If fuel and sensors check out, then investigate the ignition system.
Important Note: If you're not comfortable working on your vehicle's electrical or fuel systems, it's best to take it to a qualified mechanic. Improperly working on these systems can be dangerous. A diagnostic scan tool can help a mechanic quickly pinpoint the problem.
