Does a Noisy Fuel Pump Mean It's Bad?

Older engines were typically fitted with a mechanical fuel pump that was powered by an actuating arm driven from the engine. Newer engines have electric fuel pumps that are normally fitted close to, or inside, the fuel tank. Electric fuel pumps are a requirement for fuel injected engines; these require a higher fuel pressure than a mechanical pump can deliver. Mechanical fuel pumps were either in full working order or failed -- there was no middle ground -- and a failed pump meant the engine would not start or would grind to a halt; it ran out of gas even with a full tank. Electric fuel pumps, however, can begin to go bad without entirely failing. In this situation, aside from a decrease in engine performance, the problem is most often evidenced by noisy operation.

Electric fuel pumps share many aspects of their operation with electric drills, which may be a more familiar comparison. Electrically-energized windings spin an armature which rests in bearings, and the spinning armature rotates an impeller that moves the fuel from a resting state downstream to a pressurized state upstream.

If the impeller comes loose from the armature, a clattering noise will be heard. If the bearings fail, a knocking noise results. If contamination enters the pump from the tank, a grinding noise is common.

Fuel pump noises can be intermittent. If the noise is noticeable when the tank is close to empty, but not when it is full, the chances are there is a “pre-pump” in-tank pump-filter assembly in the system that primes the main fuel pump. In-tank pumps rely on their submersion to remain cool, and are typically sited approximately a 1/4 of the way up from the tank floor. If the vehicle is habitually operated with low fuel levels, the in-tank pump is more likely to fail prematurely.

The housing of in-tank pumps are prone to perforation because of the extremely adversarial nature of their environment, they being submersed in gasoline. The sock filter attached downstream of the in-tank pump is prone to becoming blocked, particularly in older vehicles. If an in-tank pump housing has a hole, it will not work to its optimum capacity when the level of the gasoline goes below its location. If a sock filter is blocked, this can reduce to almost nothing the amount of fuel the pump can move. These symptoms are called “starvation” in industry-speak. In either case, the reduced delivery often results in the main fuel pump making exaggerated whirring noises.

Electric fuel pumps are also prone to overheating. This issue presents as an intermittent failing, where the pump will work again if allowed to cool. Although no noises are typical of this issue, the pump should be replaced.