Quicker acceleration and better mileage... Change the injection timing advance curve...
This CAN be done on the car without removing the injection pump. On the side of the pump facing the front of the car, there's a round plate with two screws. This is where the advance mechanism lives. Before you begin, go to the dealer and get the seal kit for the advance piston housing. It'll consist of two large green o-rings, several smaller ones and an e-clip. Cost is about $5.
Loosen the cover, using a T30 Torx bit. Now you are going to remove the screws and cover. Be careful as there is a rather large spring behind the cover, as well as some spacer shims. Once the cover is off, you should find two shims between the spring and cover, and if you remove the spring, there will be one more shim. Take all of them out and look at them. Take the thickest one and set it aside... you won't be needing it. Now, smear some vaseline on both ends of the spring and stick a thin shim to each end. Insert the spring back in and put the cover back on, using a new o-ring. You must have a shim on each side of the spring, otherwise the spring will "machine" the aluminum cover and advance piston, filling your pump with fine metal filings... thus destroying the pump and injectors. Take a ride and feel the throttle response!
For those of you that have access to parts for these pumps (new or used), you can get even better throttle response and power by changing the advance spring too... Just replace the spring currently in your pump with a "lime green" colored spring. This spring has the softest spring rate and allows the pump to advance the timing MUCH sooner, with more overall advance. These springs are commonly found in early rabbits (pre 80) and Vanagon diesel pumps. Color codes from softest spring rate to hardest is as follows... Green, Gold, Red, yellow, silver, and blue. The hardest spring rates will give the LEAST timing advance.
Modified by TurboDieselTech at 6:29 PM 4-19-2007