7 - Fuel Pump Leakdown Test

This test will determine if the fuel pump will maintain pressure after the pump is turned OFF.

For this test the vehicle will be raised on the hoist and a means of controlling the fuel pump from under the vehicle is required. The Scan tool readily provides this function (refer to "Energizing the Fuel Pump"). Energizing the Fuel Pump

CAUTION: Do no not allow smoking or the use of open flames in the area where work on the fuel system is taking place. Anytime work is being done on the fuel system, disconnect the negative battery cable, except for those tests where battery voltage is required.

IMPORTANT: Battery must be at a minimum of 12 volts when performing any fuel system test. Charge battery before proceeding if below 12 volts.

1. Connect Scan tool to vehicle and turn Ignition to On.

CAUTION: Fuel supply lines will remain pressurized for long periods of time after the engine is shutdown. This pressure must be relieved before servicing the fuel system.




2. Relieve fuel system pressure (refer to "Relieving Fuel Pressure") Service and Repair
3. Raise vehicle to comfortable working position.

CAUTION: Whenever fuel line fittings are loosened or removed, wrap a shop cloth around the fitting and have an approved container available to collect any fuel.

4. Disconnect fuel feed (5/16 in.) and fuel return (3/8 in.) lines at fuel filter/pressure regulator.

NOTE: To properly utilize the fuel flow/pressure test adapter it must always be connected with the fuel feed line on the "INLET" side of the adapter and the fuel return or drain line connected to the side with the flow control (ON/OFF) valve. If not connected properly, a "zero" pressure reading will always be read. Use the appropriately sized connector fittings to hookup the adapter to the feed and return lines.




5. Connect fuel flow/pressure test adapter (SA9127E-7) to (1) feed and (2) return lines and make sure connections are firmly latched.
6. Connect fuel pressure gauge to test adapter.
7. Turn On/Off flow valve on test adapter to On.
8. Energize fuel pump.
a. Cycle On/Off flow valve at least two times over a 10 second interval.
b. Turn On/Off flow valve to Off.
c. Record fuel pressure.
9. Shut fuel pump Off and wait 5 minutes.
10. Record fuel pressure and subtract from pressure recorded in Step 8.




11. Compare pressure loss (decay) to published specification.
12. Return to "Fuel System Diagnostic Chart" and use test result to make appropriate decision.