1. Check Fuel Pressure: This is the most crucial test. You'll need a fuel pressure gauge that fits your vehicle's fuel system (check your owner's manual or a parts store for the correct fitting). The gauge connects to the fuel rail or a test port (location varies by year and model; consult a repair manual).
* Turn the key to "ON" (engine off): The fuel pump should prime and build pressure. A faulty pump may not reach the correct pressure or take excessively long. Your owner's manual or a repair manual should specify the correct fuel pressure for your engine. Low or no pressure strongly suggests a bad fuel pump.
* Engine running: Maintain the pressure reading with the engine running. Consistent pressure indicates the pump can maintain output. A drop in pressure while the engine runs suggests the pump is struggling or failing.
2. Listen for the Fuel Pump: With the key in the "ON" position (engine off), you might be able to hear the pump running briefly. It's a whirring sound that usually lasts only a few seconds. No sound could suggest a non-functioning pump or a relay problem. (However, a quiet pump might still function; the pressure test is more decisive.)
3. Check the Fuel Pump Relay: A faulty relay can prevent the pump from receiving power, mimicking a pump failure. Locate the fuel pump relay (check your owner's manual or online resources) and swap it with a known good relay of the same type (from another system in the car, if possible). If the problem goes away, you've found the culprit.
4. Inspect the Fuel Filter: A clogged fuel filter can restrict fuel flow, simulating a weak pump. Locate the fuel filter (often near the fuel tank) and visually inspect it. If it's dirty or damaged, replace it.
Important Considerations:
* Safety: Fuel is highly flammable. Work in a well-ventilated area, away from open flames or sparks. Use caution when working with fuel lines.
* Repair Manual: A repair manual specific to your 1986 Oldsmobile Ninety-Eight is invaluable for precise locations of components, wiring diagrams, and pressure specifications.
* Professional Help: If you're uncomfortable performing these tests or the problem persists, take your vehicle to a qualified mechanic. While you might save some labor cost by testing these items, incorrect diagnosis can waste your time and even cause more significant damage.
If the fuel pressure test indicates low or no pressure, even after checking the relay and fuel filter, the fuel pump is the most likely suspect. While you *can* try some of these tests without dropping the tank, ultimately, replacing the pump usually requires tank removal or specialized tools on this vehicle due to it's location.
