Fuel Pressure: Testing and Inspection
EARLY MODEL VEHICLESNote: This test assumes that there is a good ignition spark. If this is not the case diagnose and repair any ignition system problems before proceeding with fuel system testing.
Fuel Pressure Release:
Injector Harness Connectors:
1. Loosen fuel tank filler cap to relieve fuel tank pressure. Disconnect injector wiring harness at connector and connect a jumper wire from terminal #1 of the injector harness to ground. Connect a second jumper wire to terminal #2, and touch the battery positive post for no more than 5 seconds. System pressure is now released.
2. Carefully remove 5/16 fuel supply hose from the engine fuel line assembly and connect fuel pressure gauge C-3292, and hose adapter C-4749 or equivalents between supply hose and fuel line assembly.
Fuel System Views:
3. Using the appropriate tester (DRB II) or equivalent scanner, place ignition switch in "RUN" position and use Actuate Output Test "Auto Shutdown (ASD) Relay", to activate fuel pump and pressurize system, (listen for hum from fuel tank area). This test will activate the fuel pump for 1.5 second intervals. If fuel pump fails to activate, check for voltage to fuel pump, and fuel pump ground. If fuel pump has no voltage test Auto Shut Down (ASD) relay operation.
The gauge should read 100 kPa plus or minus 7 kPa, (14.5 psi plus or minus 1 psi) and hold for one minute or more.
^ If fuel pressure is below specification proceed to step 4.
^ If fuel pressure is above specification proceed to step 6.
^ If pressure is as specified fuel system is operating correctly and no further testing is necessary. If pressure bleeds off continue testing procedure to step 5.
4. If fuel pressure is below specification, move pressure gauge to fuel supply line and install between fuel tank and fuel filter. Repeat test procedure, and check fuel system pressure. If pressure is 5 psi higher than previous reading and within specification, replace fuel filter. If no change occurs in pressure proceed to step 5.
5 Gently squeeze fuel return hose. If pressure increases to specification, replace fuel pressure regulator. If no change in pressure occurs, either the fuel pump is defective or the sock type filter is obstructed. Remove pump assembly and inspect. If in tank filter is not obstructed replace the pump.
6. If fuel pressure is above 100 kPa (14.5 psi) remove fuel return hose from fuel pressure regulator end, and install a suitable hose from fuel pressure regulator output. Place the other end of the hose in a large (2 gallon minimum), clean and approved container. START engine and observe fuel pressure. If pressure is now within specification, problem is a restriction in fuel return line, or an obstructed fuel return check valve in tank. Clear return line obstruction if necessary, and/or replace fuel tank assembly if in-tank check valve is obstructed. If pressure is still above specification replace fuel pressure regulator.
LATE MODEL VEHICLES
Note: This test assumes that there is a good ignition spark. If this is not the case diagnose and repair any ignition system problems before proceeding with fuel system testing.
Injector Connectors:
Fuel Pressure Release:
1. Loosen fuel tank filler cap to relieve fuel tank pressure. Disconnect injector wiring harness at connector and connect a jumper wire from terminal #1 of the injector harness to ground. Connect a second jumper wire to terminal #2, and touch the battery positive post for no more than 5 seconds. System pressure is now released.
2. Carefully remove fuel supply hose from the engine fuel line assembly and connect fuel pressure gauge C-4799, and hose adapter C-6539 or equivalents between supply hose and fuel line assembly.
Fuel Pressure Test Equipment:
3. Using the appropriate tester (DRB II) or equivalent scanner, place ignition switch in "RUN" position and use Actuate Output Test "Auto Shutdown (ASD) Relay", to activate fuel pump and pressurize system, (listen for hum from fuel tank area). This test will activate the fuel pump for 1.5 second intervals. If fuel pump fails to activate, check for voltage to fuel pump, and fuel pump ground. If fuel pump has no voltage test Auto Shut Down (ASD) relay operation.
The gauge should read 265 kPa plus or minus 7 kPa, (39 psi plus or minus 1 psi) and hold for one minute or more.
^ If fuel pressure is below specification proceed to step 4.
^ If fuel pressure is above specification proceed to step 6.
^ If pressure is as specified fuel system is operating correctly and no further testing is necessary. If pressure bleeds off continue testing procedure to step 5.
4. If fuel pressure is below specification, move pressure gauge to fuel supply line and install between fuel tank and fuel filter. Repeat test procedure, and check fuel system pressure. If pressure is 5 psi higher than previous reading and within specification, replace fuel filter. If no change occurs in pressure proceed to step 5.
5 Gently squeeze fuel return hose. If pressure increases to specification, replace fuel pressure regulator. If no change in pressure occurs, either the fuel pump is defective or the sock type filter is obstructed. Remove pump assembly to inspect.
6. If fuel pressure is above 272 kPa (40 psi) remove fuel return hose from fuel pressure regulator end, and install a suitable hose from fuel pressure regulator output. Place the other end of the hose in a large (2 gallon minimum), clean and approved container. START engine and observe fuel pressure. If pressure is now within specification, problem is a restriction in fuel return line, or an obstructed fuel return check valve in tank. Clear return line obstruction if necessary, and/or replace fuel tank assembly if in-tank check valve is obstructed. If pressure is still above specification replace fuel pressure regulator.