7 - Fuel Pump LEAKDOWN Test

TOOLS REQUIRED:  SA9127E-7 Fuel Flow/Pressure Test Adapter

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 .

1. Connect Scan tool to vehicle and turn Ignition to ON.
2. Relieve fuel system pressure. Refer to RELIEVING FUEL PRESSURE .
   Fig 1: Relieving Fuel System Pressure

   Courtesy of GENERAL MOTORS CORP.
3. Raise vehicle to comfortable working position.
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.
   Fig 2: Connect Fuel Flow/Pressure Test Adapter (SA9127E-7)

   Courtesy of GENERAL MOTORS CORP.
6. Connect fuel pressure gauge to test adapter.
7. Turn On/Off flow valve on test adapter to ON.
8. Energize fuel pump.
   1. Cycle On/Off flow valve at least two times over a 10 second interval.
   2. Turn On/Off flow valve to OFF.
   3. Record fuel pressure.
9. Shut fuel pump Off and wait 5 minutes.
10. Record fuel pressure and subtract from pressure recorded in step  3.
11. Compare pressure loss (decay) to published specification.
    Fig 3: Fuel System Leakdown Specification

    Courtesy of GENERAL MOTORS CORP.
12. Return to FUEL SYSTEM DIAGNOSIS - FUEL SUPPLY CHART  and use test result to make appropriate decision.