In order to determine whether the fuel pump is properly priming, several key indicators and tests should be checked to ensure its functionality. Commonly, a properly primed fuel pump should generate a certain fuel pressure, usually between 30-50 psi for most vehicles. If the fuel pressure is low or inconsistent, it may indicate that the pump is not functioning correctly. A fuel pressure gauge makes the check pretty simple: It reads the pressure at the fuel rail. For example, a Honda Accord may give a reading of 45 psi at the fuel rail under normal operating conditions. If it reads considerably lower, it is symptomatic that the fuel pump is not generating the required pressure.
Also, the fuel pump should turn on instantly when the ignition is turned to the "on" position but before cranking the engine. In most vehicles, you can hear a faint hum or whine coming from the gas tank area; this is how you will know the fuel pump is on. This is particularly true with vehicles like the Toyota Camry models, where drivers report hearing a slight noise when the key is turned to the "on" position. If no noise is heard, it may indicate that the fuel pump is not priming.
Another indication that the pump is well-primed includes the behavior of the engine during start-up. A car should start up with ease, while the engine should run easily upon firing up the ignition. A faulty fuel pump or improperly primed pump may lead to the cranking of the engine without starting up, a common occurrence when there is not enough fuel flow. For instance, if a Chevrolet Silverado experiences improper priming of the pump, the engine might start but sputter or stall almost immediately after startup.
Beyond the audio and pressure indicators discussed, there is an inboard fuel system diagnostic for determining fuel pump performance relative to priming in many newer models of vehicle. Ford Mustang models use such an onboard system capable of displaying diagnostic fault codes indicating pump failure in terms of loss of prime.
On newer models, with an OBD-II system, they will give error codes for fuel delivery problems. To check for any trouble codes related to the Fuel Pump or pressure issues, a scan tool can be plugged into the vehicle's diagnostic port. For example, a code such as P0087 indicates low fuel pressure in the fuel system, which is usually symptomatic of a bad pump.
It is important to note that the state of the fuel filter or fuel lines also can determine if the fuel pump will prime correctly. A clogged fuel filter may hinder fuel flow and be unable to prime the pump properly. This holds good in older vehicles where these filters tend to get clogged up with sediments or contaminants over time.
In a nutshell, a correctly priming fuel pump should produce appropriate pressure, make a noise when the ignition is turned on, and deliver sufficient fuel to allow the engine to start easily. Any of these signs that are not met may need further diagnosis into the Vehicle's Fuel Pump system. For more information on replacement parts or professional advice, visit Fuel Pump.