Discovery 2. Manual — part 94

FUEL DELIVERY SYSTEM - V8

DESCRIPTION AND OPERATION

19-2-7

Fuel pump

The fuel pump assembly comprises a top cover which locates the fuel pressure regulator, electrical connector and
fuel pipe coupling. The top cover is attached to a plastic cup shaped housing by two metal springs. The housing
locates the pump and the fuel gauge sender unit.

The lower part of the housing is the swirl pot, which maintains a constant fuel level at the fuel pick-up. A feed pipe
from the pump to the coupling connection and a return pipe from the regulator connect between the top cover and the
housing.

A coarse filter is attached to the base of the housing and prevents the ingress of large contaminants into the swirl pot.
A gauze filter prevents particles entering the fuel pump.

Surrounding the pump is a large fine paper filter element which further protects the fuel pressure regulator, engine
and injectors from particulate contamination. The paper filter is not a serviceable item and removes the requirement
for an external in-line filter.

A non-return valve is located in the base of the housing. When the fuel tank is full, fuel pressure keeps the valve lifted
from its seat allowing fuel to flow into the swirl pot. As the tank level reduces, the fuel pressure in the tank reduces
causing the valve to close. When the valve is closed fuel is retained in the swirl pot, ensuring that the swirl pot remains
full and maintains a constant supply to the fuel pump.

A four pin electrical connector is located on the top cover of the pump and provides power feed and return for fuel
pump and fuel gauge rotary potentiometer operation. A single quick release coupling connects the fuel feed pipe to
the outer top surface of the pump.

Two metal springs are attached to the top cover and the housing of the pump. When the pump is installed it seats on
the lower surface inside the tank. The springs exert a downward pressure on the pump and ensure that the pump is
located positively at the bottom of the fuel tank.

The fuel pump has a maximum current draw of 6.5 A at 12.5 V.

On NAS vehicles with vacuum type EVAP system leak detection capability only, the fuel pump top cover is fitted with
an On Board Diagnostics (OBD) pressure sensor. This sensor has a three pin electrical connector which provides a
connection between the sensor and the ECM. The sensor is sealed in the top cover with an 'O' ring and secured with
a clip. The sensor monitors tank pressure during OBD tests of the fuel evaporation system integrity. A hose is
connected to the sensor and is routed across the top of the fuel tank and terminates at the top of the fuel filler tube.
The pipe is open to atmosphere and provides atmospheric pressure for the sensor operation.

+

ENGINE MANAGEMENT SYSTEM - V8, DESCRIPTION AND OPERATION, Description - engine

management.

Fuel pressure regulator
The fuel pressure regulator is located in the underside of the top cover. The regulator is sealed with two 'O' rings and
retained with a clip.

The regulator is connected to the fuel feed pipe at the top of the pump housing and maintains the fuel pump delivery
pressure to 3.5 bar (50 lbf.in

2

). When the fuel delivery pressure exceeds 3.5 bar (50 lbf.in

2

), the regulator opens and

relieves excess pressure back to the swirl pot via a return pipe. The regulator ensures that the fuel rails and injectors
are supplied with a constant pressure.

The fuel pump delivery pressure and pressure regulator operating pressure can be checked using a Schraeder type
valve located at the rear of the engine on the fuel rail. The valve allows the pump delivery pressure to be measured
using a suitable gauge and an adaptor and hose which are special tools.

FUEL DELIVERY SYSTEM - V8

19-2-8

DESCRIPTION AND OPERATION

Fuel gauge sender
The fuel gauge sender unit comprises a rotary potentiometer operated by a float. The float rises and falls with the fuel
level in the tank and moves the potentiometer accordingly.

Battery voltage is supplied to the potentiometer. The output voltage from the potentiometer varies according to the
resistance through the potentiometer in relation to the fuel level. The output voltage is connected to the fuel gauge in
the instrument pack. The fuel gauge receives a battery voltage input and this is compared with the output voltage from
the potentiometer. The difference between the two voltages determines the deflection of the fuel gauge pointer.

Fuel gauge reading

Tank volume litres (US Gallons) *

Sender unit resistance

ohms

Ω

FULL

95 (25)

15

3/4

71 (18.8)

36

1/2

48 (12.7)

64

1/4

24 (6.4)

110

RESERVE (fuel light ON)

11 (2.9)

158

EMPTY

0 (0)

245

*Tank volumes are approximate.

FUEL DELIVERY SYSTEM - V8

DESCRIPTION AND OPERATION

19-2-9

Injectors

1 'O' ring 2 off
2 Electrical connector
3 Steel housing
4 Filter strainer
5 Spring

6 Valve needle and armature
7 Valve seat/spray orifice
8 Plastic housing
9 Solenoid winding

An injector for each cylinder is mounted externally in the lower inlet manifold on the engine. The injector protrudes
into the inlet manifold tract, where it releases a controlled delivery of fuel into the manifold air inlet.

Each injector is sealed to the fuel rail and the inlet manifold with 'O' rings. Spring clips retain each injector to the fuel
rail and the attachment of the fuel rail clamps the injectors in the lower manifold.

The injector housing is manufactured from plastic which encapsulates a high-alloy steel housing. The steel housing
contains all components which come into contact with fuel. The plastic housing also provides the attachment for the
engine harness connector for the injector. A solenoid is located between the two housings and moves a valve needle
via an armature. The valve needle seats on a valve seat which incorporates a spray orifice plate. A filter strainer is
fitted at the connection with the fuel rail to remove any particulate matter from the fuel before it enters the injector.

When the ECM energises the solenoid, the armature moves lifting the valve needle off its seat. This allows
pressurised fuel from the fuel rail to pass through the injector housing and needle to the spray orifice. The spray orifice
controls the spray shape and fuel metering. When the solenoid is de-energised, the valve needle returns to the valve
seat, aided by a spring, closing off the injection of fuel into the inlet.

Each injector receives a battery supply voltage via a fuse in the engine compartment fusebox. The fuel delivery timing
is controlled by the ECM, which, at a precisely timed interval, provides a ground path for the injector. The completion
of the ground path operates the injector to allow fuel at pump pressure to be delivered from the fuel rail to the injector
nozzle. Each injector sprays a finely atomized spray of fuel into the inlet, where it is mixed with the intake air prior to
combustion.

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ENGINE MANAGEMENT SYSTEM - V8, DESCRIPTION AND OPERATION, Description - engine

management.

Faults for each injector are stored in the ECM and can be retrieved using TestBook. Each injector can be checked
across the two connector pins. For a correctly functioning injector a resistance of between 13.8 and 15.2 ohms at a
temperature of 20

°

C (65

°

F) should be read across the pins.

FUEL DELIVERY SYSTEM - V8

19-2-10 DESCRIPTION AND OPERATION

Operation
When the ignition switch is moved to position II, the fuel pump relay in the engine compartment fusebox is energised
by the ECM. Battery voltage is supplied from the fuel pump relay to the fuel pump which operates. If engine cranking
is not detected by the ECU within a thirty second period, the ECU will 'time-out', de-energising the fuel pump relay.

+

ENGINE MANAGEMENT SYSTEM - V8, DESCRIPTION AND OPERATION, Description - engine

management.

The fuel pump draws fuel from the swirl pot and pumps it along the fuel feed pipe to the injector fuel rail on the engine.
When the pressure in the fuel feed line reaches 3.5 bar (50 lbf.in

2

) the fuel pressure regulator opens and relieves

pressure by directing fuel back into the swirl pot. The pressure regulator is constantly opening and closing to maintain
the pressure in the fuel feed pipe and the fuel rail at 3.5 bar (50 lbf.in

2

).

The pressure is felt at each of the eight injectors connected to the fuel rail. The ECM controls the injection timing and
energises each injector to allow a metered amount of fuel at pump pressure to be injected into the inlet tract of the
inlet manifold. The atomised fuel from the injector is mixed with air from the inlet manifold before passing into the
cylinder.