Diagnosis of the fuel pump that does not prime may be challenging, with several methods and key pointers to the problem. First things first, check the voltage supply at the pump. A typical automotive fuel pump needs an invariant voltage supply in the neighborhood of 12 volts to work efficiently. According to the National Institute for Automotive Service Excellence (ASE), low voltage is considered to be the leading cause of fuel pump malfunction, responsible for about 15-20% of all pump failures in vehicles.
If voltage does not reach the fuel pump, the problem has to do with the electrical connections, fuse, or relay. Professionals in automotive repair suggest that one should check the fuel pump relay since a faulty relay will not allow the correct signal to be transmitted to the fuel pump to prime it. Indeed, about 30% of all relay failures are related to mishandling or component aging.
Another diagnostic procedure to be carried out is to see if there is any obstruction in the fuel lines. Fuel pumps, including the new high-efficiency ones, are designed to give a certain pressure to the engine. The clogging or restriction in the fuel lines may obstruct the flow of fuel, leading to failure in priming the pump. The fuel filter, for example, which is rarely remembered, may become clogged-up after 20,000 to 30,000 miles, depending on the type of vehicle and the driving conditions.
Sometimes, the problem can be with the fuel pump itself. Most fuel pumps are prone to mechanical failure, especially on higher mileage cars or those that have been exposed to harsh conditions. If the pump has been operating for more than 100,000 miles, the mechanical parts may wear out and the pump will not be able to prime. Newer fuel pumps are designed to last longer, and some newer models can go as high as 150,000 miles or more before any signs of wear begin to show.
In such cases, a diagnostic scan tool can be very effective. This tool, when plugged into the OBD-II port of the vehicle, can give valuable information on any fault codes and thus help the technicians to quickly identify issues related to the fuel system. Indeed, manufacturers like Bosch and Delphi offer diagnostic tools that can pinpoint problems with the fuel pump, fuel lines, or electrical system, saving both time and repair costs. These tools will also be able to confirm if the voltage and signal that the pump requires are in fact reaching it.
Another source of information is listening for the fuel pump. Typically, when the ignition is turned on, the fuel pump will make a brief humming noise as it primes itself. If no noise is made, then that could also be a sign that either the pump isn't working or isn't getting power. However, this is not always a reliable method since some newer pumps are much quieter than others. For reference, the 2018 Ford F-150 uses a fuel pump that was engineered to be almost silent while operating, making it even harder for users to use auditory diagnosis.
Some fuel pump failures are due to fuel quality. In the past few years, many fuel pump failures have been traced back to poor-quality fuel, especially where the use of additives is erratic. According to the Environmental Protection Agency (EPA), fuel contamination is a leading cause of system failures in motor vehicles, accounting for more than 25 percent of all engine performance problems.
The diagnosis of the fuel pump that does not prime requires a step-by-step process involving the electrical system analysis, fuel line blockages, and the use of diagnostic tools to check fault codes. For more information about symptoms and solutions on fuel pumps, visit Fuel Pump.