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The lift pump on a GM 6.5 liter turbo-diesel engine provides diesel oil to the fuel pump, which in turn supplies fuel to the injectors. When a lift pump malfunctions, the engines fuel pressure will drop. The typical symptoms of a failing lift pump will be harder starting and lower power during operation.
Step 1
Park the truck on level ground and allow engine to cool before starting. The fuel lift pump on a GM 6.5 turbo-diesel is typically located underneath the truck, under the driver seat area, inside the frame rail. You can feel and hear this pump operating when the truck is idling, which is the easiest way to determine if the pump is still functioning.
Step 2
Open the fuel filter water drain in the engine compartment, with the truck running. If the fuel lift pump is operating, diesel fuel will spray from the end of the hose. If the engine continues to idle, then the lift pump is functioning, as it is delivering more fuel to the fuel system. If the engine dies, then the lift pump is not functioning properly.
Step 3
Determine if there is air in the system. If there is air present in the fuel system, then the lift pump will be unable to provide fuel to the fuel pump. Air will enter the system if you have changed the fuel filter, run the tank dry, or even if the vehicle has sat for an extended period of time.
Step 4
Remove the fuel filter and check the housing to see if it is dry. Add some diesel fuel to the fuel filter and reconnect it to the fuel lines. Vent the air out of the system via the vent on the filter housing. If the vehicle has been sitting for an extended period it will take time for the air to purge from the system. Open the air bleed and turn over the engine to bleed air out of the filter.
Crank the engine while you aim a test light at the lift pump to ascertain proper operation. You can typically hear the lift pump if it is engaging when you crank the engine, on GMs 6.5 turbo-diesels the lift pump will not engage when the ignition is turned to the ON position.
Items you will need
- Comprehensive set of hand tools including wrenches and socket set
- Test light
- Small can of diesel fuel
- Clean-up rags
