A good fuel pump is absolutely essential for easy starting and smooth performance at all engine speeds and loads. Fuel injected engines are very sensitive to fuel pressure and volume. If a pump can’t deliver normal pressure and volume, the engine may misfire, lack power or fail to start. Depending on the type of pump that is in a vehicle (roller vane, gerotor or turbine), pump output is essentially a direct function of its speed. Turbine-style pumps typically operate at speeds up to 7,000 RPM or higher.
To run at full speed, the fuel pump needs full voltage (13.5 volts). Pulse Width Modulated (PWM) pumps have variable speeds that increase with demand, but still need peak voltage to achieve maximum output. If the supply voltage to the fuel pump is low by only 2 volts, it may run 20 percent slower than normal causing a drop in fuel pressure and volume. If there’s no voltage to the pump, it won’t run at all and the engine won’t start.
A weak electric fuel pump that is not operating at normal speed can be tricky to diagnose because it may still provide enough pressure and flow for the engine to start and idle but starve the engine for fuel at higher engine speeds and loads. A weak pump may be a worn pump, but it might also be the result of something else such as a loose or corroded wiring connection in the fuel pump circuit, an open or short in the fuel pump wiring harness, a loose, broken or corroded ground connection, bad relay or blown fuse.
There may be a fault in the PCM that is preventing it from energizing the fuel pump relay, such as a bad driver circuit or a communication fault with the anti-theft system. The vehicle might also have a pinched or plugged fuel line, a plugged fuel filter or a clogged fuel pump inlet sock due to rust and sediment in the fuel tank. On Ford vehicles, a tripped inertia safety switch also will disable the fuel pump circuit.
If a fuel pump has failed (quit working altogether) or fails to meet minimum pressure and volume specifications for the application, it needs to be replaced with a new pump. The new pump should be a quality product from a reputable manufacturer, and it should meet the vehicle manufacturer’s pressure and volume requirements. Some of the newest pump designs feature a “brushless” three-phase motor that eliminates brush wear and extends the life of the pump. Some cheap-quality fuel pumps may not perform the same as the original fuel pump or a quality aftermarket pump. Also, many cheap pumps lack the durability of an OEM or quality aftermarket pump.
Replacing an in-tank fuel pump is a pain, so it’s important to sell your customer a quality pump that will only have to be replaced once. In recent years, some fuel pump manufacturers have replaced older vane- and gerotor-style pumps with turbine pumps. Turbine pumps generally run smoother and quieter than other designs. Consequently, if a new pump looks different than a customer’s old fuel pump, don’t fret (assuming you looked up the correct part number) because it should perform the same or better than the original.