6 - Fuel Supply LEAKDOWN Test

This test will determine if the fuel supply system, up to the fuel rail and injectors, will maintain pressure after the fuel pump is turned off.

1. Remove air induction tube.
   Fig 1: Relieving Fuel System Pressure

   Courtesy of GENERAL MOTORS CORP.
2. Relieve fuel system pressure. Refer to RELIEVING FUEL PRESSURE .
3. Remove fuel feed line retainer clip attachment screw (10 mm hex).
4. Disconnect fuel feed line at fuel rail.
   1. Connect fuel feed line directly to pressure gauge using (309728) quick-connect adapter (3/8" x 1/4").
      Fig 2: Connecting Fuel Feed Line Directly To Pressure Gauge

      Courtesy of GENERAL MOTORS CORP.
      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.
   2. If using the fuel flow/pressure test adapter, connect "INLET" to fuel feed line and assure that flow valve is OFF.
5. Connect pressure gauge to test adapter.
   Fig 3: Connecting Pressure Gauge To Test Adapter

   Courtesy of GENERAL MOTORS CORP.
6. Energize fuel pump. Refer to ENERGIZING THE FUEL PUMP  for a minimum of 10 seconds.
   1. Record fuel pressure.
   2. Repeat this procedure a minimum of two times.
7. Shut fuel pump Off and wait 5 minutes.
8. Record fuel pressure and subtract from pressure recorded in step  6.
9. Compare pressure loss (decay) to published specification.
   Fig 4: Fuel System Leakdown Test Table

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