What Is a Tandem Pump, and How Do I Maintain It?

What Is a Tandem Pump, and How Do I Maintain It?


– Tandem pump: description of the technology

– Maintenance of the tandem pump

– Prices and suppliers of the tandem pump

The tandem pump is related to a particular technology of high-pressure diesel direct injection systems, the pump injectors, and serves as both a vacuum pump and a fuel pump. We tell you all about the usefulness of this automotive part in our article!

Tandem pump: description of the technology

Vacuum pump function


The air vacuum of the tandem pump is mainly used to power the brake assist (brake booster) and various pneumatic controls:

– turbocharger solenoid valve;

– EGR solenoid valve;

– air conditioning valves, etc.

The diesel engine has the particularity of not having throttle valves like gasoline cars: there is no air depression (negative pressure) created directly by the engine’s suction.

Note: In the diesel engine, the intake pressure varies between the atmospheric pressure and the turbo pressure by about 1 bar.

The tandem pump compensates for this through the vacuum pump, which is positioned at the end of the camshaft and is driven by the camshaft, creating the necessary air vacuum.

Fuel supply: fuel pump function

The unique feature of the tandem pump is that it also supplies fuel to the pump injectors: it incorporates the feed pump, juxtaposed with the vacuum pump, which takes advantage of the camshaft drive to convey the gas from the tank to the pump injectors via channels inside the cylinder head.

In addition to standard rail technology used in most new generation TDI engines, pump injectors are mainly utilized in Volkswagen Group engines.

Each cylinder has a short injector with an individual high-pressure pump driven by the camshaft.

Please note: This robust and reliable technology is on the way out due to increasingly strict emission standards.

Maintenance of the tandem pump


The malfunctions noted are the breakage of the drive, like any vacuum pump (loss of braking assistance caused by a hard brake pedal) and losses of seals that can have significant consequences on the operation and reliability of the engine.

Three fluids coexist in this organ (air-oil – diesel), which can end up in contact by default:

– fuel and air:

Whether it is by the depression of air generated by the pump or the outside air, the air in the fuel system will cause a disarming of the system with difficulties or impossibility of starting.

– fuel and oil:

Even more annoying, diesel in the lubrication circuit causes the oil level to rise, with the risk of the oil-diesel mixture being sucked in by the air intake circuit.

As a result, the engine has difficulty starting and, in the worst case, runs away at high speed (which can destroy the engine and the turbo).

Replacing the tandem pump

If it is a leakage problem, an alternative to replacement is to repair the pump by replacing the seals. Otherwise, you must replace the tandem pump.

Note: The repair of the pump is a careful operation with severe consequences if it is not carried out correctly. Therefore, it should be carried out by a professional or a well-informed and organized amateur, under optimal conditions of cleanliness.

Price and suppliers of the tandem pump

Bosch fuel pump

The tandem pumps must be original brands (Bosch, Pierburg, Luk): a seal kit is charged $55.

They are supplied by:

– the manufacturer’s network, from $300 to $500;

– by automotive suppliers and technical parts specialists, from $250 to $400;

– by the Internet sites of car parts whose referencing is generally more limited; the prices are advantageous: $200 on average.

As previously mentioned, the reconditioning must be done by a professional:

– removal + reconditioning = 1h30 of work or on average $120;

– the replacement alone (removal/installation) is approximately $60 for 45 minutes of work.

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