300Tdi Discovery
BRAKES
9
DESCRIPTION AND OPERATION
Petrol engine vacuum system
The vacuum necessary to operate the brake servo on
petrol engine vehicles is provided by the engine inlet
manifold. During normal operation of the brakes only a
small volume of air is drawn from the servo and into
the inlet manifold or plenum chamber. However any
excessive air leaks due to damage in the brake servo
system or manifold hose connection, will effect the
mixture strength and ECM fuelling calculations on
engines equipped with an MFI system.
Diesel engine vacuum system
As the diesel engine inlet system does not produce
depression sufficient to operate the brake servo, it is
necessary to install an engine driven vacuum pump.
During normal operation of the brakes only a small
volume of air is drawn from the servo by the vacuum
pump. However as the pump exhausts air into the
engine crankcase atmosphere, an air leak due to
damage in the brake servo system or pump hose
connection, may cause excessive crankcase
pressure.