On the 2.5 P.I. a Lucas Mk. II petrol
injection system replaces carburettors. This system delivers a fine spray of
precisely timed and measured fuel to the air intakes via injectors. The
mixture is then compressed and spark ignited in the usual manner.
The principles of operation as well as the
relevant maintenance, overhaul, adjustments and fault finding procedures
that can be associated with petrol injection are hereunder described.
It is envisaged that faults such as excess
fuel consumption, poor performance, erratic running, etc., will be
attributed to the fuel injection system, whereas they are more likely to
emanate from other systems of the vehicle. It is, therefore, important to
establish the correct functioning of the ignition, electrical, cooling and
other systems and that sufficient clean fuel is available.
DESCRIPTION OF P.I. CIRCUIT
Using the schematic illustration (Fig.1)
for reference, a brief description of the system is as follows:
Fuel from the tank (2) is gravity fed to a
reservoir (4) from which it is drawn, via an in-line filter to an
electrically driven pump (5). Pressurized fuel from the pump is passed to
the metering unit (1) which meters and delivers fuel to each injector (9) in
Fuel line pressure from the pump is
maintained at 106 to 110 p.s.i. by a pressure relief valve (6) which returns
excess fuel to the tank.
The metering unit is driven in conjunction
with the ignition distributor. Fuel is used to lubricate the metering unit
and is then fed back to the tank.
The fuel reservoir acts as an anti-surge device,
preventing loss of fuel to the pump on sharp turns, steep hills and sudden
stops. A pipe, vented to the fuel tank, prevents air locks in the system.