The VW injection pump is an electronically controlled Bosch VE distributor pump. The basic design was used in all 1996-2003 North American VW diesels. 2004 and later VW TDIs used the pumpe duse injection system which had no injection pump because the fuel injectors acted like injection pumps. See 1000q: fuel injection generational differences for more details on distributor pump, pumpe duse, and common rail systems.
Minor changes are mounting and electrical connector changes. The biggest changes are between the 11mm automatic and 10mm manual transmission pumps. The 11mm pump moves more fuel. All top cover seals and fuel temperature sensors are interchangeable and easily replaced. The quantity adjusters are also interchangeable in all models but the electrical connectors are different in the 1Z/AHU engine for 1996-1999 engines and ALH 1998-2003 engines. The cold start injector and fuel shut off solenoid are also user serviceable. All other seals and internal parts are harder to service so professional rebuilding and maintenance is recommended.
Below is a rough translation of a rebuild of a renault 1.6L diesel injection pump. It's similar to a VW TDI injection pump but has slightly different internals and is not electronically controlled. I can't read French - if you can, please help improve this translation. The original post is from this French site: http://www.forum-auto.com/pole-technique/section12/sujet293129.htm I take no credit for the following info, it's only an english mirror of the french site and is saved because it's an excellent Bosch injection pump disassembly. I added some notes to help describe the function of each part and make up for a poor translation.
Here is a picture of the pump disassembled to give an idea of how many parts
First, clean everything thoroughly.
Start with one of the fuel output hard lines unions. Shown below are the various parts from one of the hard line and unions: the valve, valve end, and a new union and threaded connection.
Assembled and in the pump head:
Start by reassembling the stator of the transfer pump. This is what
delivers fuel to the injection pump under suction. Pay attention to the position of the holes relative to the holes at the bottom of the pump housing,
circled in green.
The rotor and its pallets:
first place it in the rotor:
then add the pallets using a grip with needle nose pliers:
then the lid of the pump:
in position with its screws
Now the main shaft:
For assembly, note the two keys and the assembly grease.
then the disc spacer
and finally the key:
Place it in the injection pump
Now you need to assemble the rollers:
Place the roller in, paying attention to the position of the hole
places the assembly in the pump housing:
Note the position of the roller: it is sometimes in, sometimes out.:
The door roller, when advanced, has to be able to fit in here:
Note that the axis is pointing up:
The piston in place:
Pay attention to its position! Note the hollow part of the piston which receives the spring and it's relation to the active hole of evacuation to the transfer pump:
Again, check the axis in its place.
Lock it with the pin
And lock the pin with its clip:
Use a new o-ring here:
On the other side, the spring and other parts.
Then finally the electric "surcalor". Some models may have this part or a stopper. On VW TDI, this is the cold start advance solenoid. I believe that is what "surcalor" is.
Then this part which finishes this section:
Then add the rollers. They are shown here on their support separated from the pump: pay attention to the bent washer in relation to the pin.