Fuel System Diagnosis

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. Disconnect the 5/16 fuel supply hose from the engine fuel line. Connect fuel system pressure gauge C-3292 or equivalent between fuel supply hose and engine fuel line.
3. Using the appropriate tester (DRB II) or equivalent place ignition switch in RUN position and actuate ATM button to activate fuel pump and pressurize system. If fuel pump fails to actuate, check for voltage to fuel pump, and fuel pump ground. If fuel pump has no voltage proceed to ASD RELAY TEST. After actuating fuel pump the gauge should read 330 kPa plus or minus 14 kPa (48 psi plus or minus 2 psi).
- If fuel pressure is below specification proceed to step 4.
- If fuel pressure is above specification proceed to step 5.
- If pressure is as specified fuel system is operating correctly and no further testing is necessary. Reinstall fuel hose using a new rolled edge clamp, and torque to 1 Nm (10 in. lbs.).
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, 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.
5. If fuel pressure is above 394 kPa (57 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 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.