A fuel pump that delivers normal pressure may still cause driveability problems if it can't deliver enough fuel volume to meet the engine's needs. A fuel volume test may therefore be the best way to evaluate the pump's condition.
A fuel volume test measures the volume of fuel delivered over a specified interval. This test can be done by connecting a fuel flow gauge into the fuel supply line, or by disconnecting the fuel return line from the fuel pressure regulator and connecting a hose from the regulator to a large container. Caution: Make sure there are no open sparks or flames nearby while doing this test!
With the engine off, energize the pump and measure the volume of fuel delivered during the specified interval of time. As a rule, a good pump should deliver about one quart of fuel in 30 seconds.
Causes of low fuel volume delivered include a worn fuel pump, a plugged fuel filter or inlet sock in the tank, obstructed fuel line or nearly empty tank. Don't forget that low voltage at the pump can also prevent it from running fast enough to generate adequate fuel flow. The pump's supply voltage should be within half a volt of normal system voltage. If it is low, check the wiring connectors, relay and ground.
Friday, February 6th, 2009 AT 11:39 AM