Why fault persists after replacing fuel pump

A replacement fuel pump that has wrong specifications will create drivability issues as it won't operate within designed specifications.

Are you having drivability issues with every non stock fuel pump? These are some of the specifications that should be checked when buying a fuel pump to ensure that the correct fuel pump type is used.

1. Flow (volume)

2. Pressure

3. VoltageAt times, defective or weak fuel pumps are passed as okay simply because the technician feels that the pressure that the pump is delivering is okay.

As engine load/horse power demand increases, there is need for more volume of fuel. Hence, a pump that appears to have sufficient pressure may not be able to meet up with fuel volume demand.

Ensure that the new pump meets both pressure and volume demand of the car's engine.

Note that some fuel pumps are volume rated at zero line pressure. When fitted into the car, restrictions introduced will increase the pressure and volume will drop. Hence, that volume rating is not practical when the fuel pump is in operation in the car.For instance, a pump originally rated at 0.5 gallons per minute might become 0.4 gallons per minute.

The best thing to do is to check out for pumps that have ratings like 0.5 gallons per minute at 40 psi.

The voltage at which the pressure and volume is rated is also important. Some pumps are rated at 13.5V. At periods when the alternator cannot meet up with normal voltage requirement, the pressure and volume will definitely drop. Therefore, it is better to get a fuel pump whose pressure and volume are rated at 12 volts instead of higher voltage rating.

In some systems, manifold vacuum is used to regulate the pressure in order to maintain same effective pressure (at the injectors). In some returnless fuel supply systems, pulse width modulated power is supplied to the fuel pump to vary its output (some people get it wrong here by connecting the electrical fuel pump directly to battery in order to tap power from it to fix a fuel pump power supply problem). In these PWM systems, one might measure a voltage lower than 12 volts. Maybe 10 volts, 7 volts and so on. Hence, it is not right to rely on fuel pump's terminal voltage in pulse width modulated systems.

If these fuel pump specifications are looked into while purchasing a new unit, one should not have drivability problems as a result of fuel pump malfunction unless the fuel pump is weak or dead due to age.