There are several warning signs that can point to a failing fuel pump.
Incomplete fuel combustion, fuel diluting the engine oil, and an engine that suddenly stalls while driving are just some of the problems that can result from operating a vehicle with a failing fuel pump. Recognizing the warning signs early can help prevent more serious damage and an expensive repair bill.
A failing fuel pump may be unable to maintain the required fuel pressure or may not deliver enough fuel to the engine. As a result, starting the vehicle can become difficult.
The driver may have to try several times before the engine finally starts. After repeated attempts, enough fuel reaches the system for the engine to run normally.
This problem may not happen every time. Intermittent hard starts can indicate that the electric motor's brushes are worn out. For example, the engine may start easily when cold in the morning but fail to start after a short drive or after the vehicle has been sitting in hot weather.
As resistance in the electrical circuit increases, contact between the motor brushes can be interrupted. The fuel pump then struggles to maintain the pressure the system needs.
When a vehicle noticeably loses power and acceleration, while the spark plugs are known to be in good condition, the fuel pump is worth checking. If the pump cannot maintain the required fuel pressure, the engine may lose power and the vehicle will feel slower than it normally does.
The problem is especially noticeable during acceleration, when climbing a steep hill, passing another vehicle, or towing a heavy load. In these situations, the engine needs more fuel, but a damaged pump may not be able to deliver enough.
Under load, the engine may struggle to maintain higher RPMs and feel as though it is running out of breath. Pressing the accelerator produces a weak response. In some cases, the vehicle's electronics may deliberately limit engine power to prevent more serious damage.
A failing fuel pump can make fuel delivery inconsistent, causing the vehicle to lose its smooth power delivery. The driver may feel jerking or surging while driving. Depending on how much fuel pressure has dropped, the symptoms can range from barely noticeable to severe.
Another common symptom is hesitation when the accelerator is pressed quickly. During acceleration, the engine may briefly lose power, followed by a jerk as acceleration resumes.
This can happen when a contaminated or worn fuel pump delivers fuel to the cylinders with a delay. Instead of responding smoothly, the engine hesitates and then suddenly regains power.
If the fuel pump problem becomes severe because of excessive wear, heavy contamination, or an electrical issue, the symptoms may progress beyond hesitation and jerking. The engine can stall completely.
At idle, this can happen when the fuel system cannot maintain stable pressure. The air-fuel mixture becomes too lean, and engine speed begins to fluctuate. Eventually, the engine may stall. It may not restart immediately, and when it does, it may run very roughly.
An engine that stalls while the vehicle is moving is much more dangerous. Power is suddenly lost and the vehicle continues rolling under its own momentum. Attempts to restart the engine may be unsuccessful.
If the vehicle is allowed to sit for a while, particularly in a cooler location, the fuel pump may begin working again and the engine may restart. However, continuing to drive under these conditions is not advisable because it can put the driver and other motorists at risk.
A properly functioning fuel pump generally does not produce unusual noises. The only sound drivers normally notice is a brief, light hum when the ignition is switched on.
If grinding, clicking, whining, or buzzing begins coming from the area around the fuel tank, it can indicate that the fuel pump is operating under excessive load. That extra strain may be caused by worn motor brushes, a damaged commutator, or a worn impeller. In severe cases, the pump could eventually seize.
Unusual noises can also be caused by a clogged fuel-pump strainer. When the strainer becomes contaminated, the pump has to work harder to move fuel through the system.
When a failing fuel pump does not deliver enough fuel, the air-fuel mixture can become too lean. The vehicle's sensors detect the condition and send the appropriate information to the engine control module. As a result, the Check Engine light may illuminate on the dashboard.
The Check Engine light by itself does not specifically indicate a fuel-pump problem. However, if the vehicle's electronics detect a lean air-fuel mixture or critically low fuel pressure, there is a good chance that something is wrong with the fuel delivery system. An electronic diagnostic scan can help confirm or rule out a fuel-pump problem.