Diesel fuel injection system, leak testing: Notes

WARNING: This page is about a different car, the 1996 Volkswagen Jetta. However, it is still accessible from the selected car via links, so may be relevant.

Run engine at idle speed and open the throttle several times to remove any air in the system.
Disconnect fuel return line at injection pump.
Attach the adapter line to the injection pump in place of the return line.
Clamp the fuel supply line closed at the fuel tank with a clamp.
Build up a pressure of 1.0-1.5 bar (15-21 psi) using VAG 1274 hand pump.
It may be necessary to pump up the system several times because of air in the system that is compressed when the system is pressurized.
If the continues to drop, locate and eliminate the leak.

Fig 1: Attaching Adapter Line To Injection Pump In Place Of Return Line

NOTE:

The leak can be isolated by repositioning the hose clamp downstream of the fuel filter.
The fuel return line can be pressurized by connecting the adapter to the fuel supply line. The return and supply lines at the fuel tank as well as the supply line at the outlet of the fuel filter must then be disconnected.