Fuel Pressure: Testing and Inspection

Figure 8:

The fuel system is equipped with a vacuum assisted fuel pressure regulator (Figure 8). With engine at idle speed, system fuel pressure should be approximately 214 kPa (31 psi) with the vacuum line connected to the regulator. With the vacuum line disconnected from the regulator, fuel pressure should be approximately 269 kPa (39 psi). This is 55-69 kPa (8-10 psi) higher.

Figure 7:

Figure 9:

(1) Remove the protective cap at the fuel rail (Figure 7). Connect the 0-414 kPa (0-60 psi) fuel pressure gauge (from Gauge Set 5069) to test port pressure fitting on fuel rail (Figure 9).

(2) Note pressure gauge reading. Fuel pressure should be approximately 214 kPa (31 psi) at idle.

(3) Disconnect vacuum line (hose) at fuel pressure regulator (Figure 8). Note gauge reading. With vacuum line disconnected, fuel pressure should rise to approximately 269 kPa (39 psi).

Fuel pressure should be approximately 55-69 kPa (8-10 psi) higher with vacuum line removed from regulator. If not, inspect pressure regulator vacuum line for leaks, kinks or blockage. If vacuum line checks OK and fuel pressure does not rise approximately 8-10 psi after disconnecting the vacuum line, replace fuel pressure regulator.

The fuel pressure regulator is not adjustable.

(4) If fuel pressure exceeds 45 psi, check fuel return line/tube for kinks or obstructions.

If the previous tests checked good, fuel pump pressure is correct. If pump pressure was low, proceed as follows:

(5) Release fuel system pressure. Refer to the Fuel Pressure Release Procedure. Service and Repair

(6) Disconnect the 5/16 inch fuel return line quick-connect fitting at fuel rail. For procedures, refer to Fuel Return Line, Service and Repair. Service and Repair

Figure 10:

(7) Connect Fuel Line Pressure Test Adapter Tool number 6539 (5/16 in.) between the disconnected fuel return line and fuel rail (Figure 10).

(8) Connect a 0-689 kPa (100 psi) pressure gauge to Adapter Tool 6539.

WARNING: THE FUEL SYSTEM PRESSURE IN THE FOLLOWING TEST MAY EXCEED 100 psi. BEFORE STARTING TEST, VERIFY GOOD CONNECTIONS AT ENDS OF ADAPTER TOOL 6539. BE SURE TOOL IS LOCKED ONTO FUEL RAIL AND FUEL RETURN LINE. PULL FIRMLY ON ENDS OF TOOL TO VERIFY.

(9) Activate the fuel pump and pressurize the system using the DRB or equivalent scan tool.

(10) MOMENTARILY pinch the rubber hose portion of adapter tool 6539. Pressure should rise to approximately 75 psi within two (2) seconds. DO NOT pinch hose for longer than three (3) seconds.

If fuel pump pressure rises to approximately 75 psi within two seconds, pressure is operating at its maximum and is correct.

If fuel pump pressure does not rise to approximately 75 psi within two seconds, proceed as follows:

(11) Release fuel system pressure. Refer to Fuel Pressure Release, Service and Repair. Service and Repair

(12) Raise and support vehicle.

(13) Disconnect fuel supply line at inlet (fuel tank side) of fuel filter. Connect Fuel Line Pressure Test Adapter Tool number 6631 (3/8 inch) between fuel filter and fuel supply line.

WARNING: THE FUEL SYSTEM PRESSURE IN THE FOLLOWING TEST MAY EXCEED 100 PSI. BEFORE STARTING TEST, VERIFY GOOD CONNECTIONS AT ENDS OF ADAPTER TOOL 6631. BE SURE TOOL IS LOCKED ONTO FUEL FILTER AND FUEL SUPPLY LINE. PULL FIRMLY ON ENDS OF TOOL TO VERIFY.

(14) To activate the fuel pump and pressurize the system, use the DRB scan tool. Refer to Computers and Control Systems, Testing and Inspection, Procedures for DRB operation.

MOMENTARILY pinch the rubber hose portion of adapter tool 6631. Pressure should rise to approximately 75 psi within two (2) seconds. DO NOT pinch hose for longer than three (3) seconds.

If fuel pump pressure now rises to approximately 75 psi within two seconds, but this pressure could not be met at the fuel rail, check for a plugged or restricted fuel filter. Also check the fuel supply line between fuel filter and fuel rail for kinks or obstructions. Proceed to the Fuel Pump Capacity Test under Fuel Pump, Testing and Inspection. Fuel Pump Capacity Test