A correctly priming fuel pump is important to ensure that fuel reaches the engine with proper pressure and flow. On most vehicles, the fuel pump primes when the ignition key reaches the “on” position. It energizes the fuel pump to pressurize the fuel system before engine startup. If the fuel pump does not prime properly, then the car may not start easily or may not start at all.
One good indicator of whether a fuel pump is priming like it should is the noise of the pump when the key is turned to the “on” position. You should hear a faint humming or buzzing sound from the fuel tank when you turn the key to the on position before starting the engine. The sound you hear is the pump drawing fuel from the tank and pressurizing the system. The sound should only last for a few seconds, and not hearing it may mean that the fuel pump is not operating properly. According to General Motors, this noise in most cases is absent in vehicles made after 2005. The absence of this noise would typically indicate a failed pump or relay.
Sometimes, a diagnostic scan tool will be able to monitor the fuel pump pressure. A good fuel pump would hold fuel pressure within a specified range. As a typical fuel pressure for most automobiles, it usually lies within the range of 30-60 psi (pounds per square inch) according to the make and model. A low reading might suggest a malfunctioning fuel pump with or without proper priming. According to Bosch, a fuel pressure gauge can be helpful in determining whether or not the pump is operating within the necessary specifications.
Another key factor in determining if the fuel pump is priming correctly involves checking the fuel system’s pressure retention. Once the vehicle is turned off, the fuel system should hold its pressure for a period of time. If the fuel pressure drops rapidly, this may indicate a leak in the system or that the fuel pump is not maintaining pressure as required. Usually, the design for fuel pumps in all vehicles is such that they hold pressure upwards of 10 minutes when the vehicle is turned off.
In most cases, problems with fuel pumps emanate from malfunctioned relays or fuses. According to Ford, when either the fuel pump relay or fuse fails, the pump will not be able to properly prime or operate. You can check the relay or fuse for any visible damage like corrosion or a blown fuse to see if it is the cause of the problem. Also, a digital multimeter will be able to test voltage at the relay socket for verification of operation.
Besides, a weak or worn-out fuel pump may not be able to prime well, which will lead to inconsistent fuel delivery. This would include car hesitation upon startups or stalling after startup, which may signify that the fuel pump is not producing adequate pressure. For instance, owners of Honda vehicles say that one of the major signs of a fuel pump that is about to fail often results in stalling upon acceleration or inability to start right after the car has stayed idle for some time.
Sometimes, the problem can be related to a clogged fuel filter that blocks the fuel pump from getting the correct flow of fuel. Toyota suggests that the fuel filter should be changed every 30,000 miles to ensure efficiency in the functioning of the pump. A clogged fuel filter can put excessive load on the pump, which may prevent it from priming correctly.
The fuel pump is properly priming if it hums when the ignition is on, it achieves the required pressure for fuel, and the system shows it holds pressure when the engine is turned off. What might go wrong that will keep the fuel pump from working correctly: a faulty relay or fuse or a filter that is clogged. For accurate replacement parts, check out Fuel Pump.