Fuel Return System Diagnosis

FUEL RETURN SYSTEM DIAGNOSIS

DIAGNOSTIC FAULT INFORMATION

IMPORTANT: Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Testing and Inspection

CIRCUIT/SYSTEM DESCRIPTION
Fuel is used to cool and lubricate the fuel injectors and the fuel injection pump. The fuel return system is designed to return this fuel to the fuel tank. If the high side fuel pressure becomes excessive, the fuel rail pressure relief valve releases the fuel into the fuel return system. The return fuel travels through the fuel cooler to the fuel tank.

DIAGNOSTIC AIDS
Bent or pinched fuel return lines may cause an external fuel leak or engine performance concerns.

SPECIAL TOOLS REQUIRED
J 44581 Fuel Line Disconnect Tool

CIRCUIT/SYSTEM VERIFICATION
Inspect the fuel return hoses and lines on the engine and chassis for any external fuel leaks.

CIRCUIT/SYSTEM TESTING

IMPORTANT: DO NOT apply more than the specified air pressure to the return line.

1. Disconnect the fuel return line at the engine.
2. Remove the fuel filler cap.
3. Apply 1 psi of air into the fuel return at the engine and listen for air flowing from the tank at the filler tube.
4. If air flow was not detected, disconnect the fuel return line at the fuel sender and retest using 1 psi of air.
- If air flow was present, replace the fuel sender assembly.
- If no air flow was present, inspect for a restricted or a damaged fuel return line. Repair or replace the fuel return line.

REPAIR INSTRUCTIONS

IMPORTANT: Always perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Fuel Return Pipe Replacement
Fuel Sender Assembly Replacement