1. Verify "Power" is Actually a Problem:
* Is the pump running *constantly*? This is the most serious issue. A constantly running pump will drain your battery and could damage the pump itself.
* Is the pump running *when it shouldn't*? (e.g., key off). This is less serious but still needs fixing.
* Are you measuring actual voltage at the pump's connector? Don't just assume power is there. Use a multimeter to measure the voltage at the pump connector with the ignition in different positions (off, on, cranking). You should have voltage only when the ignition is in the "on" or "crank" position.
2. Investigate the Circuit:
The fuel pump circuit in a 1987 Silverado typically involves several components beyond just the relay:
* Inertia Switch: This safety device cuts power to the fuel pump in a collision. It's usually located under the dash or in the engine compartment. Check for a reset button and make sure it hasn't tripped.
* Fuel Pump Inhibitor Switch: This switch prevents the engine from starting if the clutch isn't fully depressed (manual transmission). If your truck is automatic, ignore this.
* Wiring Harness: Look for any chafed, damaged, or corroded wires between the relay, the inertia switch, the fuel pump, and the PCM (Powertrain Control Module). Pay close attention to the connectors; they can be a common failure point.
* PCM (or ECM): While less likely, a faulty PCM could be sending a signal to the fuel pump even when it shouldn't. This requires more advanced diagnostics.
* Ground: A poor ground connection can cause all sorts of electrical gremlins. Check the ground wire connected to the fuel pump and its connection points for corrosion or looseness.
3. Testing Steps:
* With the ignition OFF: Disconnect the fuel pump wiring connector. Measure the voltage at the connector. There should be zero voltage. If you still have voltage, you have a short circuit somewhere in the wiring before the connector.
* With the ignition ON: Reconnect the connector. Measure the voltage at the connector. There should be battery voltage. If not, your problem is between the relay and the pump.
* With the ignition ON: Turn on the key and listen carefully. If the fuel pump is making a humming or whirring sound, then even if the flow is weak, it indicates the pump itself is working.
* Check the fuses: Although you've changed the relay, double-check all relevant fuses.
4. Seeking Help:
If you're not comfortable working with automotive electrical systems, it's best to take your Silverado to a qualified mechanic. Diagnosing electrical problems can be tricky, and incorrectly diagnosing could lead to further damage or injury. A scan tool might be helpful for a mechanic to diagnose any PCM issues.
