Overflow Valve
Description
The overflow valve is located on the side of the injection pump (Fig. 58). It is also used to connect the fuel return line (banjo fitting) to the fuel injection pump.
Operation
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 opens at approximately 97 kPa (14 psi). If the check valve within the assembly is sticking open, fuel drainage of the injection pump could cause hard starting. 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.
Diagnosis And Testing
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 97kPa (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 N·m (24 ft. lbs.) torque.
Removal
The overflow valve (pressure relief valve) is located at the outside of fuel injection pump (Fig. 58). It connects the fuel return line (banjo fitting) to the pump. The valve has no internal serviceable parts and must be replaced as an assembly. Two sealing gaskets are used. One gasket is located between pump and banjo fitting. The other is located between the banjo fitting and end of valve.
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.
Installation
The overflow valve (pressure relief valve) is located at the outside of fuel injection pump (Fig. 58). It connects the fuel return line (banjo fitting) to the pump. The valve has no internal serviceable parts and must be replaced as an assembly. Two sealing gaskets are used. One gasket is located between pump and banjo fitting. The other is located between the banjo fitting and end of valve.
(1) Install new sealing gaskets to valve.
(2) Install valve through banjo fitting and into pump.
(3) Tighten to 30 N·m (24 ft. lbs.) torque.
Few notes...
Here is a close up of the bleed hole in the overflow valve. This picture is magnified X10 so you can even see the tiny hole used to bleed air from the system.
There is a lot of controversy about the operation of the overflow valve on a VP44 injection pump. From my personal opinion that the overflow valve is a last check valve to hold the pressure up to 14 PSI for the injection pump. As for the bleed hole in the side that hole is so small it can't possibly create enough flow to aid in cooling the VP44 unless the overflow valve is opened.
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