1. Verify Relay Functionality:
* Visual Inspection: Carefully examine the fuel pump relay itself. Look for any signs of damage, burnt contacts, or corrosion.
* Swap with a Known Good Relay: The best way to test the relay is to swap it with another relay of the same amperage rating in your Blazer (like the horn relay, for instance, many are interchangeable). If the fuel pump works with the swapped relay, your original relay is bad. If it doesn't, the problem lies elsewhere.
2. Check for Power and Ground at the Relay:
* Power: With the ignition ON (but not cranking), use a test light or multimeter to check for power at the power input terminal of the fuel pump relay. There should be 12V present. If not, trace the power wire back towards the fuse box, checking for blown fuses related to the fuel pump circuit.
* Ground: Check for a good ground connection at the ground terminal of the relay. A multimeter should show a near-zero resistance to ground. Poor ground connections are a frequent cause of electrical problems.
3. Check Power at the Fuel Pump Wiring:
* With the relay in place: Using a test light or multimeter at the wiring harness connector that plugs into the fuel pump, check for power at the appropriate wire with the ignition ON. If there's no power here, the problem is between the relay and the fuel pump itself.
* Direct Power Test (Caution!): As a final test, ONLY with the pump OUT of the tank, connect power directly to the pump wires, but ONLY IF you are 100% sure you are using the correct wires and have a way to safely isolate the connection. This can help determine if the pump is indeed defective even after replacing it.
4. Check the Inertia Switch:
Many GM vehicles have an inertia switch that cuts power to the fuel pump in the event of a collision to prevent post-crash fires. This switch is usually located under the dash or in the engine compartment and can be reset by pushing the button.
5. Wiring Harness Inspection:
If power isn't getting to the relay or the fuel pump, there's likely a break, short, or corrosion somewhere in the wiring harness. This requires a careful visual inspection of the wiring, especially in areas that are prone to chafing or damage. Look for any damaged, frayed, or disconnected wires between the relay and the fuel pump.
6. PCM (Powertrain Control Module) Issues:
In some rare cases, a faulty PCM might prevent the fuel pump relay from being energized. Diagnosing this requires a scan tool capable of reading codes from the PCM.
Important Safety Notes:
* Always disconnect the negative battery terminal before working on the fuel system.
* Be aware of fuel vapor and take necessary precautions in a well-ventilated area.
* Never work on the fuel system with a lit cigarette or any open flame nearby.
* If you are not comfortable performing these checks, it's recommended to take your vehicle to a qualified mechanic.
By systematically following these steps, you should be able to isolate the problem and get your fuel system working again. Remember to check for blown fuses early on.
