A failing fuel pump usually shows up as sputtering or loss of power at highway speed or under load, hard starting, a whining noise from the fuel tank, or an engine that cranks but will not start. A clogged fuel filter causes similar hesitation and hard starting, and a faulty fuel pressure regulator makes the engine run too rich or too lean. A fuel pressure test tells them apart.
Bad fuel pump symptoms
- Sputtering, surging or loss of power under load or at highway speed
- Hard starting or long cranking, especially when hot
- A loud whine from the fuel tank
- Cranks but will not start
- Stalling, sometimes in hot weather
Clogged fuel filter symptoms
- Hesitation or stumbling when accelerating hard
- Rough idle and misfires; see engine misfire
- Hard starting
Many newer vehicles have a filter inside the tank with the pump, so check whether yours has a separate serviceable filter.
Fuel pressure regulator symptoms
- Black smoke and a fuel smell, from running rich; see exhaust smoke colors
- Lean running and hesitation, if pressure is too low
- Fuel in the vacuum hose, on return-style systems with a vacuum-referenced regulator
- Poor fuel economy and hard starting
How to diagnose
- Connect a fuel pressure gauge to the test port and compare key-on, idle and loaded readings with the specification.
- Listen for the pump priming when the key is turned on.
- Check the pump fuse, relay and wiring before replacing the pump.
- On direct-injection engines, the high-pressure pump is separate from the in-tank pump; scan data shows both pressures.
Running the tank very low often shortens pump life, because the fuel helps cool the pump. Contaminated fuel and a clogged filter also make the pump work harder, so replace the filter on schedule where it is serviceable.
Replacing a fuel pump
Most modern pumps sit inside the tank as a module with the sending unit and strainer. Depending on the vehicle, it is reached through an access panel under the rear seat or bed, or by lowering the tank. Replace the strainer and seal with the pump, check the wiring and connector for heat damage, and relieve fuel pressure before opening any line.
Fuel systems for boosted engines
Superchargers and E85 need much more fuel. For supercharged mid-2003 to 2013 C5 and C6 Corvettes, the ECS Stage 1 E85 Fuel System ($1,832.60) adds a second pump switched on by boost, and the ECS Stage I Fuel System ($1,483.90) is the gasoline version; see what is E85?
More guides: car won’t start · fuel filter · fuel pressure regulator · fuel pump sizing · car loses power when accelerating · car hesitates when accelerating · how long a fuel pump lasts.
Trouble codes: P0087 Fuel Rail Pressure Too Low · P0171 System Too Lean Bank 1 · P0230 Fuel Pump Primary Circuit · P0627 Fuel Pump Control Circuit · P0231 Fuel Pump Secondary Circuit Low · P0232 Fuel Pump Secondary Circuit High · all OBD2 codes.
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