All Buses and Vanagons with fuel injection also have a closed circuit fuel delivery system comprised of:
1) Fuel tank
2) Fuel hoses and tubing to/from engine
3) Fuel pressure regulator
4) Electric fuel pump
The fuel pump is controlled by the fuel injection system’s electronic control unit (ECU) via a fuel pump relay. When the ignition key is turned to the RUN position, the ECU tells the fuel pump to run for about 1½ seconds. So, if you turn your ignition key ON and don’t hear the pump running continuously, that is normal. When you turn the ignition key to START, the ECU tells the fuel pump to run continuously as long as you have the key in the START position. Once the key is put back in the RUN position, if the engine does not start, the fuel pump stops. If the engine is running, the ECU tells the pump to continue to run.
The fuel pump is supplied with fuel on the inlet side via gravity feed from the fuel tank; there is no in-tank “pre-pump” on Buses or Vanagons. This works really, really well on Buses and Syncro (4WD) Vanagons where the fuel tank is directly above the fuel pump. It does not work so well on 2WD Vanagons that have a relatively flat fuel tank that is not very much higher than the fuel pump.
The one (and only) external fuel pump provides fuel supply and pressure to the engine’s fuel injectors via fuel hoses and tubing. All injectors get the same fuel supply. Downstream from the fuel injectors is a fuel pressure regulator, which restricts the fuel that is returning to the fuel tank, which increases the pressure upstream where the fuel injectors are located. After the fuel passes through the pressure regulator, it is plumbed back to the fuel tank. Thus, the fuel circulates continuously. In fact, the fuel pump moves about 10 times more fuel than the engine actually uses, on average. This is why adding more or larger fuel pumps does nothing to improve performance.
From 1980 to about 1984, Vanagons were fitted with a small square pre-filter before the fuel pump. This filter (133-133-511) had a 7mm inlet nipple and a 12mm outlet nipple. The fuel tank on a 1980-85 Vanagon has a 7mm outlet nipple. The electric fuel pump on all Vanagons has a 12mm inlet nipple. The pre-filter also acted as a sort of adaptor. Sometime in 1984, Vanagons were also fitted with a post-filter (0-450-905-030) and also kept the pre-filter. Then, at some point in 1985, they eliminated the pre-filter and replaced it with a little 7mm/12mm adaptor fitting. Finally, in 1986, VW changed the design of the fuel tank, and the nipple coming out of the tank on all 2WD Vanagons was modified to 12mm, which eliminated the need for any pre-filter or adaptor. It was at this time that the Syncro was introduced, which was designed from the get-go with a fuel tank that has a 12mm nipple, and no pre-filter was used.
On Vanagons fitted with the pre-filter, the combination of this small filter, small tubing size, and the relatively flat design of the 2WD Vanagon fuel tank would cause the fuel pump to starve for fuel at the inlet side, which created cavitation. This cavitation causes the fuel pump to make a buzzing noise. The noise would not be so bad if it were not actually hurting the pump. This is because the fuel that flows through the fuel pump is what lubricates it and keeps it cool. Cavitation negatively affects both the cooling and lubrication.
That is the reason VW eliminated the small filter before the pump—and increased the size of the hose and nipple between it and the tank—to insure an ample, non-obstructed fuel supply to the pump. The pre-filter was not only redundant and strange, but it was also tiny and clogged much too easily. By contrast, the 0-450-905-030 post-filter is very common and very large, so it usually lasts at least 30,000 miles. The nipples (inlet and outlet) are both 7mm, which matches the outlet nipple of the fuel pump and the plastic fuel line that continues on. Thus, installation is straight forward. The GoWesty fuel filter upgrade kit contains all you need to update a Vanagon that has a fuel filter before the pump.
A noisy fuel pump may mean it is worn out and possibly on its way to leaving you stranded. But, it could also just be a pump that is being operated improperly. As stated above, if the pump is starved for fuel—it will make noise. Also, if there is not enough back-pressure, that could cause it to make noise, too. The back pressure in the fuel supply system is controlled by the fuel pressure regulator, which keeps the fuel supply at around 35psi. So, if you have a noisy pump and are trying to figure out why—you need to make sure there is no obstruction on the intake side and proper back pressure on the outlet side. So, before you condemn a noisy fuel pump, be sure these two criteria are met.