Fuel Pressure Test
Warning: Fuel system pressure must be released before a fuel system hose or component is disconnected.1. Perform fuel system pressure release.
2. Remove fuel supply hose quick connector from the chassis lines (at the engine).
Fuel Gauge And Adapter:
3. Connect fuel pressure gauge, to Fuel Pressure Test Adapter 6539, or equivalent. Install the adapter between fuel supply hose and chassis fuel line assembly.
Fuel Line Adapter:
Caution: When using the ASD Fuel System Test, the ASD relay and fuel pump relay remain energized for 7 minutes or until the test is stopped, or until the ignition switch is turned to the OFF position.
4. Place the ignition key in the ON position. Using a scan tool, access ASD Fuel System Test. The ASD Fuel System Test will activate the fuel pump and pressurize the system.
^ If the gauge reads the pressure shown in the Fuel Pressure Specification, further testing is not required. If pressure is not correct, record the pressure and remove gauge. Specifications
^ If pressure is below specifications, proceed to Fuel System Pressure Below Specifications. If pressure is above specifications, proceed to Fuel System Pressure Above Specifications.
Fuel System Pressure Below Specifications
If the fuel pressure reading in step (4) was below specifications, test the system according to the following procedure.
Warning: Fuel system pressure must be released before a fuel system hose or component is disconnected.
1. Perform Fuel Pressure Release procedure.
2. Install Fuel Pressure Gauge C-4799 and Fuel Pressure Adapter 6433 in the fuel supply line between the fuel tank and fuel filter.
3. Using the DRBII scan tool, with the ignition key in the ON position, repeat the ASD Fuel System Test.
^ If pressure is at least 5 psi higher than reading recorded in step (4) replace fuel filter.
^ If no change is observed, gently squeeze return hose. If pressure increases, replace pressure regulator. If the gauge reading does not change when the return hose is squeezed, the problem is either a plugged inlet strainer or defective fuel pump.
Fuel System Pressure Above Specifications
If the fuel pressure reading in step (4) was above specifications, test the system according to the following procedure.
Warning: Fuel system pressure must be released before a fuel system hose or component is disconnected.
1. Perform Fuel Pressure Release procedure.
2. Install Fuel Pressure Gauge C-4799 and Fuel Pressure Adapter 6433 in the fuel supply line (Fig. 7) between the fuel tank and fuel filter.
3. Remove the fuel return line hose from the fuel pump at fuel tank. Connect Fuel Pressure Test Adapter 6541 to the return line. Place the other end of adapter 6541 into an approved gasoline container (minimum 2 gallon size). All return fuel will flow into container.
4. Using a scan tool, with the ignition key in the ON position, repeat the ASD Fuel System Test.
^ If pressure is now correct, replace fuel pump assembly.
^ If pressure is still above specifications, remove fuel return hose from chassis fuel tubes (at engine). Attach Fuel Pressure Test Connect Adapter 6541 to the fuel return hose and place other end of hose in clean container (Fig. 8). Repeat test. If pressure is now correct, check for restricted fuel return line. If no change is observed, replace fuel pressure regulator.