Fuel Filter

I think the fuel filter is worth mentioning here as a fuel injection component mainly because clean fuel is extremely important to a fuel injection system. Dirty fuel can lead to clogged injectors and all kinds of headaches.

The fuel filter is mounted near the pump, in the fuel line upstream of the pump, i.e. the fuel flows through the filter before it flows through the pump. This is important not only to make sure that the pump gets clean fuel but because a filter on the pressure side can be dangerous. If the filter were to become clogged and fuel flow was significantly restricted, theoretically fuel pressure could build to dangerous levels and rupture fuel lines, causing gas leaks and possible fire hazards. In practice, this probably wouldn't happen as the pressure limiter in the fuel pump would prevent it, but engineers don't like to tempt fate and it's considered bad practice to put a fuel filter on the pressure side of the system.

The filter is a somewhat large rectangular plastic box with a filter element designed to catch even very small particles. There is a paper filter element and immediately after that is a strainer. Charles O. Probst, in his Bosch fuel injection book, mentions that the paper filter has a medium pore size of 10 micrometers.

The filters on our beloved Volkswagens have to be replaced every so often. You usually know when you have to replace it by how the van starts bucking and jerking at high rpm, meaning fuel starvation due to a clogged filter. Of course, other things can cause those symptoms, but a clogged filter is always a possibility.