1. Check the Fuel Pump Relay:
* Location: Find your fuel pump relay. The location varies slightly depending on the year and trim, but it's usually in the under-hood fuse box or a separate relay center. Your owner's manual or an online forum specific to your vehicle year and model can help pinpoint it.
* Testing:
* Visual Inspection: Look for any obvious signs of damage (burns, corrosion).
* Swap with a known good relay: This is the best test. If you have another relay of the same amperage rating (check the relay itself), swap them temporarily. If the pump starts working, the relay was bad.
* Check for power at the relay: With the ignition key "ON," use a test light or multimeter to check for power at the relay's power input terminal. If there's no power, the problem is upstream of the relay.
2. Check the Fuel Pump Circuit:
* Power at the Fuel Pump: If the relay seems okay, you'll need to check for power directly at the fuel pump's wiring connector. This requires access to the pump (usually under the vehicle, near the tank) and involves disconnecting the connector to test. Caution: Exercise extreme caution; fuel systems can be dangerous.
* Grounding Issues: A poor ground connection can interrupt the fuel pump circuit. Trace the ground wire from the fuel pump and make sure it's securely connected to a good ground point.
3. Ignition System:
* Ignition Switch: A faulty ignition switch can prevent power from reaching both the ignition system and the fuel pump. It's less likely to affect both simultaneously but possible. A mechanic would usually need to test the switch's output to diagnose this.
* Ignition Coil: A bad coil won't produce spark. Testing a coil requires a multimeter or a specific coil tester.
* Crank Position Sensor (CPS) or Distributor (if equipped): These sensors provide the signal to the ignition system to fire the spark plugs. A faulty sensor will prevent sparking. These require more specialized testing equipment or a mechanic's expertise.
* Ignition Control Module (ICM): This module controls the ignition timing and spark. A faulty ICM can cut off spark entirely.
4. Other Potential Issues:
* Blown Fuse: While less likely to affect both simultaneously, check all fuses related to the ignition system and fuel pump.
* Wiring Harness Damage: Check for any damaged, corroded, or loose wiring, especially near the fuel pump and ignition components. Rodents are a common culprit for chewed wires.
Troubleshooting Order:
1. Fuel Pump Relay: Start here; it's the easiest and most likely culprit given both the spark and fuel pump issues.
2. Fuses: Check relevant fuses.
3. Fuel Pump Power: Check power at the pump itself.
4. Ignition System Components: Proceed to testing the ignition coil, CPS/distributor, and ICM if the fuel pump issue is resolved but there is still no spark.
5. Ignition Switch: Consider this last if all else fails.
Important Considerations:
* Safety: Work on the fuel system requires caution. Avoid sparks and open flames near the fuel tank. Disconnect the battery's negative terminal before working under the vehicle.
* Professional Help: If you're not comfortable working with automotive electrical systems, it's best to take the vehicle to a qualified mechanic. Diagnosing electrical issues can be challenging.
By systematically checking these components, you'll be able to pinpoint the source of the problem and get your Blazer back on the road. Remember to consult a repair manual specific to your 1986 Chevy Blazer S10 2.8L for detailed diagrams and component locations.
