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Fuel System Pressure Test

  1. Relieve fuel system pressure. See the FUEL SYSTEM PRESSURE RELEASE under FUEL PRESSURE  . Connect a 0-60 psi (0-4.2 kg/cm2 ) fuel pressure gauge to test port on fuel rail. Start engine and bring to operating temperature.
  2. With engine at idle, measure fuel pressure with fuel pressure regulator vacuum line connected. See the FUEL SYSTEM PRESSURE SPECIFICATIONS  table. If fuel pressure is high, go to next step. If fuel pressure is low, go to step 5).
  3. Inspect fuel return line for kinks and blockage. Disconnect fuel pressure regulator vacuum line and measure fuel pressure. Fuel pressure should increase 8-10 psi (.6-.7 kg/cm2 ) when vacuum line is disconnected. See FUEL SYSTEM PRESSURE SPECIFICATIONS  table.
  4. Reconnect vacuum line and note gauge reading. Ensure pressure readings are as specified. If fuel pressure is not higher with vacuum line disconnected, inspect pressure regulator vacuum line for leaks, kinks or blockage. Fuel pressure regulator is not adjustable; if vacuum line is okay, replace fuel pressure regulator.
  5. If fuel pressure is low, relieve fuel system pressure. See FUEL SYSTEM PRESSURE RELEASE under FUEL PRESSURE  . Disconnect fuel return line at fuel rail. Connect 5/16" Fuel Line Pressure Test Adapter (6539) between fuel rail and fuel return line. Connect a 0-100 psi (0-7.0 kg/cm2 ) fuel pressure gauge to test adapter.
    WARNING: Fuel system pressure may exceed 100 psi (7.0 kg/cm2 ) during next test step. Ensure test adapter and pressure gauge connections at fuel system lines are secure. Pull firmly on connections to verify. During fuel pump operation, DO NOT  pinch any fuel test adapter hose for longer than 3 seconds.
  6. Connect scan tool to Data Link Connector (DLC). DO NOT  start engine. Using scan tool, activate fuel pump and pressurize fuel system. Momentarily pinch rubber hose of test adapter between pressure gauge and fuel return line connection. Fuel system pressure should increase to approximately 75 psi (5.3 kg/cm2 ) within 2 seconds. DO NOT  pinch hose for more than 3 seconds. If fuel pressure increases to 75 psi (5.3 kg/cm2 ) within 2 seconds, fuel pump is operating correctly. If fuel system pressure does not increase as specified, go to next step.
  7. Relieve fuel system pressure. See FUEL SYSTEM PRESSURE RELEASE under FUEL PRESSURE  . Disconnect fuel pressure test adapter at fuel rail and connect fuel return line. Disconnect fuel supply line at fuel filter. Connect 3/8" Fuel Line Pressure Test Adapter (6631) between fuel supply line and fuel filter. Connect a 0-100 psi (0-7.0 kg/cm2 ) fuel pressure gauge to test adapter.
  8. Using scan tool, activate fuel pump and pressurize fuel system. Momentarily pinch rubber hose of test adapter between fuel filter and pressure gauge. Fuel system pressure should increase to approximately 75 psi (5.3 kg/cm2 ) within 2 seconds. DO NOT  pinch hose for more than 3 seconds.
  9. If fuel pressure increases to 75 psi (5.3 kg/cm2 ) within 2 seconds, fuel pump is operating correctly. If 75 psi (5.3 kg/cm2 ) was reached at fuel pump and not at fuel rail, check for a plugged fuel filter or fuel supply line between filter and fuel rail. Relieve fuel system pressure and replace fuel pump if pressure does not increase as specified.
FUEL SYSTEM PRESSURE SPECIFICATIONS

Application (1) psi (kg/cm2 )
Vacuum Line Connected 31 (2.18)
Vacuum Line Disconnected 39-41 (2.7-2.9)
(1) Fuel pressure measured at engine idle.
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