Diesel feed pumps on HGVs: what they do and how they fail
The diesel feed pump, sometimes called the lift pump, is the low-pressure supply pump that draws fuel from the tank and feeds the high-pressure injection pump. On modern common rail diesel systems, the feed pump typically maintains a feed pressure of around 3 to 8 bar. If this pressure drops, the high-pressure pump struggles to generate the required injection pressure, and the engine loses power, runs roughly, or fails to start.
Feed pump failure is often misdiagnosed. A basic fuel pressure test at the feed pump outlet takes a few minutes and rules out a supply problem before any expensive components are removed. Common failure modes are wear in the pump internals on high-mileage engines, a failed check valve, and contamination from water in the fuel.
Frequently Asked Questions
How do I test a diesel feed pump on an HGV?
Connect a fuel pressure gauge to the feed pump outlet line and crank the engine. Compare the reading against the manufacturer's specified feed pressure. A reading significantly below specification confirms pump failure or a supply restriction. Check for a blocked fuel filter or collapsed inlet hose before condemning the pump.
What symptoms does a failing diesel feed pump cause?
Hard starting when cold, power loss under load, rough running, and fuel starvation at high engine speeds are all consistent with low feed pump pressure. These symptoms are also shared with fuel filter blockage and high-pressure pump wear, so a fuel pressure test is the first diagnostic step.
Is a diesel feed pump a service item on HGVs?
Feed pumps are not typically included in standard service schedules but should be considered on high-mileage engines showing fuel system symptoms. Fuel filter replacement at the correct service interval is the best preventive measure.
Does Truckstop Group stock feed pumps for all HGV makes?
We stock diesel feed pumps for the main HGV makes including DAF, Scania, Volvo, MAN, Mercedes-Benz, Iveco, and Renault. Call us on 01527 598 000 with your chassis number if you need help identifying the correct pump.
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