How to remove the lift pump, disassembly, and FAQ, for Volkswagen TDI
The lift pump is the name for the electric fuel pump inside the fuel tank of your VW TDI. The main difference with most car fuel pumps is the pressure and how the fuel system works. In most gasoline cars, the fuel pump is responsible for supplying about 40-80 psi of fuel pressure to the fuel injectors. The fuel injectors won't spray without fuel pressure and the engine will stall. Most gasoline cars have no secondary fuel pump or bypass valves.
Pre pumpe duse (1996-2003 in North America)
2003 and earlier VW TDI sold in North America didn't have any electric fuel pumps because the timing belt driven injection pump draws fuel from the fuel tank and pressurizes it. You can add a lift pump to pressurize the fuel lines. This will add power at high rpm on highly modified VW TDI by ensuring adequate fueling. It also makes priming a lot easier if you run the fuel lines dry. Unless you have at least a larger than stock turbo, I would add other power modifications like chip tuning or injector nozzles first. See 1000q: basic power upgrades for more details.
Pumpe duse TDI (2004-2006 Volkswagen TDI)
2004 saw the introduction of pumpe duse to North America. European TDI already had it for a few years. The lift pump works at about 5-10 psi to move fuel to the tandem pump (dual vacuum and fuel pump) on the cylinder head where it is pressurized again to the fuel rail and injectors. The camshaft lobes press on the fuel injector heads and it pressurizes the fuel to about 29,000 psi!
Early lift pumps have bypass valves so that if the electric motor fails (which was a problem with early pumps), the engine can still run off the fuel sucked by the tandem pump. Later lift pumps don't have bypass valves so if the electric motor fails, the engine will stall. Luckily, most later pumps are more reliable but there are still occasional reports of failure and engine stalling. You can also put a T and one way valve on the pump's pressure line as a bypass valve.
Some part numbers for the lift pumps are VW# 1k0 919 050 d, VW# 1k0 919 050 j, and VW# 1j0 919 050 b.
Common rail TDI (2009+ Volkswagen TDI)
These use the same lift pumps as the pumpe duse. However, after leaving the lift pump it goes to a high pressure fuel pump on the cylinder head which pressurizes the fuel into the accumulator rail to about 20-28,000 psi!
How the TDI lift pump works
NOTE - The lift pump pictured below from a 2005 VW Passat TDI. Function of early lift pumps is also described.
All lift pumps
Lift pumps flow between .8 and 1 gallon per minute, depending on model. The electric pump flows more but any excess exits through a high pressure release valve. Whenever you turn the ignition key to "ON", the lift pump runs for a second to prime the system, then shuts off to prevent excess running. As you start the engine, the lift pump runs constantly until the engine is shut off.
Early lift pumps (no longer sold, VW# 1j0 919 050 b)
The pump is all light tan and manufactured by POM. Fuel enters through a large screen in the bottom of the assembly, the tub. It then passes a fine screen filter and into the electric pump. From there, it goes to a high pressure release valve/intake nozzle/bypass valve. Any excess fuel exits the pressure valve into the tub, the rest goes to the engine. If the electric fuel pump dies the bypass opens and the engine can still run as long as vacuum is held by the tandem pump (second fuel pump). If the intake nozzle is clogged, no pressure can get to the engine and most if not all fuel will come through the bypass valve. Return fuel is emptied back into the fuel tank. It's interchangeable with the newer style.
Aftermarket and newer lift pumps (shown below)
The pump has grey or white top, white bottom/tub, made by VDO. Fuel enters through a check valve in the bottom of the assembly, the tub. It then passes a fine screen filter and into the electric pump. From there, it goes to the engine. Any excess pressure is released through a high pressure release valve that empties into the check valve inlet. Excess fuel returning from the engine comes back into the tub. If the electric fuel pump dies the engine will stall from a lack of fuel. It's interchangeable with the older style.
Procedure and disassembly
Lift the rear seats or carpet in the trunk to reveal the fuel tank access cover. Remove the 3x phillips screws.
Lay plastic and paper around the interior before removing the pump. Diesel is an oil and your interior will smell like fuel if it soaks into the carpet.
Release the electrical plug and the fuel feed/return lines. The fuel lines have small clips at the base holding them down. Do not forcefully pry them off. Push the fuel line down and push the clip in to release.
Unscrew the fuel tank cap ring. It's very tight - during installation, make sure it's tight or else fuel can leak out. To turn it, use a punch or screwdriver to hit the teeth. VW sells a special wrench for this cap.
You can now remove the lift pump. Tilt it to clear the fuel level sensor. There's a lot of fuel inside so use a bucket to catch all the fuel that will come out during removal.
To disassemble the lift pump, first remove the 4x torx screws on the back.
Then you can get access release all the clamps holding the white tub.
There's a fine screen to protect the motor.
The return line empties into the tub. The advantage of this is that if the fuel is close to gelling temperature (well below freezing or fuel not winterized properly), the return line will help prevent gelling and fuel starvation. This is because the return line is warmed by the being pressurized at the engine and by radiant heat off the engine. The disadvantage is that cold fuel is better for performance and efficiency. The engine fuel temperature sensor tells the car's computer how warm the fuel is and then adjusts engine operating parameters.
fuel level sensor
suction bypass nozzle
Clogged suction bypass nozzle can cause problems at low fuel levels or high fuel temperatures
test pump with 12v, blue/red is power (check your wiring schematic to confirm),
brown is ground.