MAN high-pressure fuel pumps

Replacing a high-pressure fuel pump

The high-pressure pump takes fuel at feed pressure and raises it to the level injection demands, which on a modern common rail engine means well over a thousand bar. On older mechanical D-Series engines the in-line injection pump does two jobs at once: it pressurises the fuel and it meters and times the delivery to each cylinder. Either way it is a precision machine, and the fuel passing through it is the only thing lubricating its internals.

That is why pumps fail. Water in the fuel breaks down the lubricating film and corrodes the plunger and barrel. Abrasive dirt scores those same surfaces until the pump can no longer build or hold pressure. Running the tank dry does the damage in seconds rather than months. The result is hard starting, low power, rough running, and on common rail engines a pressure fault logged by the ECU.

Before condemning a pump, rule out the cheap causes first. A blocked filter, a collapsing suction hose, a leaking union or a failing feed pump will all starve the high-pressure pump and produce very similar symptoms. Replacing a pump that was only ever short of fuel is an expensive way to fix a five euro problem.

Our recommendations when a pump is replaced:

• Find the cause before fitting the new pump. If water or dirt killed the old one, it will kill the new one too
• Clean the tank, renew every fuel filter and drain the water separator before the engine runs again
• Check the injectors and the high-pressure lines. A pump that has failed internally sends metal debris downstream, and fitting a new pump to a contaminated system simply repeats the failure
• Work scrupulously clean. Cap every open line and union, because contamination introduced during fitting is a common cause of early failure
• Observe timing and calibration. A mechanical injection pump must be timed to the engine correctly, and set up on a test bench if it has been overhauled
• Prime and bleed the system properly before cranking, so the new pump is never turned dry

Every pump we supply is genuine MAN, comes with a 2-year warranty and can be dispatched worldwide. Send us the model and serial number from your engine's data plate and we will confirm the correct pump before anything is ordered.