I've recently upgraded the bald 29" road tyres that came with mine with some 235/85/16 Muddies (courtesy of 4wdTV
) and noticed that it lacked a fair bit mid and upper range after the upgrade. Being used to the V8 in the Rangie, i decided that something had to be done......
The tdi utilises a Bosch VE injection pump which is used on a number of diesel vehicles. There are some very easy mods which can be done to these which have a marked impact on performance. Note that these mods will raise your EGT and should only be performed if you know what you're doing, if you f*ck anything up, you could destroy your motor!!!
Firstly, check out this image....
This shows what the the injection pump looks like, note where the smoke adjustment screw is and the diaphragm, these are the important bits.
On this top bit is something that looks like a welsh plug, this can be removed by levering out with a small screw driver. Under this plug is the smoke screw which is a T25 torx bit surrounded by a 13mm locknut. Undo the nut, and now mark the position of the torx screw. This is can be quite tight.
Turn this screw between 1 and 1.5 turns clockwise. I turned mine 1 full rotation (360 degrees) to err on the safe side before i install an EGT gauge. Adjusting this will improve the low manifold boost pressure responsiveness.
The next step is to remove the cover held down by four screws (see above photo). This will allow access to the diaphagm and star wheel.
Once removed mark the position of the diaphagm. The diaphragm can now be pulled out. You will note that the bottom of the pin is not symmetrical. By rotating the diaphragm approximately 90 degrees clockwise you will improve full throttle response.
While you have the diaphagm removed you should be able to see the starwheel. Rotating this clockwise increases the tension on the spring which improves the fuel load delivery rate. Again, note the position of the star wheel. Rotate approximately 180 degrees.
Now put back together and see how much it smokes. There should not be much black smoke as this indicates unburnt diesel and most likely high EGT's. These settings can be tweaked more but do so at your own risk. High EGT's will kill a diesel! You have been warned!
Check out LRE for further discussion on this. I got most of my info from there but a lot of it was not very clear.
Also, for more info....
http://dodgeram.org/tech/dsl/more_power/Power_ve.htm
http://www.cs.rochester.edu/u/jag/vw/en ... jpump.html
Good luck, it will really transform your Tdi. Mine goes as good as a Td5 now and is much safer and more enjoyable to drive.
I got it done for $9.96 (had to buy a bigger screwdriver for the diaphragm cover). 
