Why wrongly selected fuel pump won't perform well
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.
1. Flow (volume)
Ensure that the new pump meets the pressure and volume demand of the car.
Note that some pumps are volume rated at zero line pressure. When fitted into the car, restrictions will be introduced and volume will drop. Hence, that volume rating is not practical when the fuel pump is in operation.
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 that the alternator cannot meet up to normal voltage requirement, the pressure and volume will drop. Therefore, it is better to get a pump whose pressure and volume are rated at 12 volts instead of higher voltage.
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 directly to battery voltage to fix 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.