Overflow Valve Test

Fig.66 Overflow Valve Location:

Fuel volume from the fuel transfer (lift) pump will always provide more fuel than the fuel injection pump requires. The overflow valve (a check valve) is used to route excess fuel through the fuel return line and back to the fuel tank. Approximately 70% of supplied fuel is returned to the fuel tank. The valve is located on the side of the injection pump (Fig. 66). It is also used to connect the fuel return line (banjo fitting) to the fuel injection pump. The valve opens at approximately 97 kPa (14 psi). If the check valve within the assembly is sticking, low engine power or hard starting may result.

If a Diagnostic Trouble Code (DTC) has been stored for "decreased engine performance due to high injection pump fuel temperature", the overflow valve may be stuck in closed position.

A rubber tipped blow gun with regulated air line pressure is needed for this test.
1. Clean area around overflow valve and fuel return line at injection pump before removal.
2. Remove valve from pump and banjo fitting.
3. Discard old sealing gaskets.
4. Set regulated air pressure to approximately 97 kPa (14-16 psi).
5. Using blow gun, apply pressure to overflow valve inlet end (end that goes into injection pump).
6. Internal check valve should release, and air should pass through valve at 97 kPa (14-16 psi). If not, replace valve.
7. Reduce regulated air pressure to 10 psi and observe valve. Valve should stay shut. If not, replace valve.
8. Install new sealing gaskets to valve.
9. Install valve through banjo fitting and into pump.
10. Tighten to 30 Nm (24 ft. lbs.) torque.