What the Perkins 1004 / 1006 Mechanical Lift Pump does
The lift pump draws diesel from the tank and feeds it, through the filters, to the injection pump. On Perkins 1004 and 1006 engines it is a mechanical diaphragm pump driven from the camshaft, usually with a hand lever for priming.
When the diaphragm or valves wear, the pump cannot keep the injection pump full. The engine may start and idle but starve when load comes on — a fault that is easily mistaken for a governor or injection pump problem.
Signs it needs replacing
- Hard starting, especially after the generator has stood unused.
- Engine hunting or losing power when load is applied.
- Air bubbles in the fuel at the filter or bleed screw.
- Diesel leaking from the pump body, or diesel in the engine oil.
- The hand-priming lever has no resistance.
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- A photo of the engine dataplate — the engine serial number decides the exact part.
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Fitting notes
The pump bolts to the engine block over the camshaft, and the lever must sit correctly on the cam when fitted. Afterwards the whole fuel system must be bled of air — filters, injection pump and, if needed, injector pipes. Always check the filters and the tank pickup at the same time: a blocked filter makes a good lift pump look faulty.
Frequently asked questions
How do I know it is the lift pump and not the filters?+
Fit new filters and bleed the system first. If the engine still starves under load and the priming lever feels weak, the lift pump is the likely cause.
Does the generator need bleeding after the pump is changed?+
Yes. Air must be bled from the filters and injection pump before the engine will run properly.
Can diesel in the oil come from the lift pump?+
Yes — a ruptured diaphragm can leak fuel into the crankcase. If your oil level is rising or smells of diesel, stop the engine and have it checked.