Volkswagen turbo diesel engines incorporate a boost pressure enrichment mechanism on the fuel injection pump, to increase the amount of fuel injected when the turbocharger is providing more air. The boost enrichment housing, shown in Fig. 5-29, incorporates a diaphragm and push rod connected to the injection pump distributor plunger and to intake manifold pressure. An increase in manifold pressure, due to turbocharger boost, acts on the boost enrichment diaphragm, and in turn the injection pump distributor plunger, to increase the amount of fuel delivered to each injector.

Turbo diesel boost enrichment is pre-set at the factory, and the boost enrichment housing can only be replaced as a unit with the fuel injection pump. The only maintenance necessary is to see that the housing vent is open when a new pump is installed. See Fig. 5-29.

Fig. 5-29.

Boost pressure enrichment housing. Connection from intake manifold shown at a. New injection pump with a vent hose (1) must have sealing clamps (left arrow) removed. Rubber cap (2) must have tip cut off cap (right arrow) for venting.