1 General information and
precautions
General information
The fuel system consists of a fuel tank,
situated at the rear of the car, with an electric
fuel pump immersed in it, a fuel filter, fuel feed
and return lines, and the throttle body
assembly (which incorporates the single fuel
injector and the fuel pressure regulator), as
well as the engine management electronic
control unit (ECU) and the various sensors,
electrical components and related wiring. The
air cleaner contains a disposable paper filter
element, and incorporates a flap valve air
temperature control system, which allows
cold air (from the outside of the car) and warm
air (heated by the exhaust manifold) to enter
the air cleaner in the correct proportions.
To reduce emissions and to improve
driveability when the engine is cold, the inlet
manifold is heated by the cooling system
coolant and by an electric pre-heater system.
Mixture enrichment for cold starting is a pre-
programmed function of the system.
The ECU fully controls both the ignition and
fuel injection systems, integrating the two in a
complete engine management system; refer
to Chapter 5B for information on the ignition
side of the system.
The Rover/Motorola Modular Engine
Management System uses ECU-controlled
single-point injection (MEMS-Spi) and the
speed/density method of airflow
measurement. The whole system is best
explained if considered as three sub-systems;
the fuel delivery, air metering and electrical
control systems.
The fuel delivery system incorporates the
fuel tank with an electric fuel pump (immersed
in a swirl pot to prevent aeration of the fuel)
inside it. When the ignition is switched on, the
pump is supplied with current via the fuel
pump relay, under the control of the ECU; the
pump feeds petrol via a non-return valve (to
prevent fuel draining out of the system
components and back to the tank when the
pump is not working) to the fuel filter, and
from the filter to the injector. Fuel pressure is
controlled by the pressure regulator, which
lifts to allow excess fuel to return to the tank
swirl pot, where a venturi causes the returning
fuel to draw cool fuel from the tank into the
swirl pot. In the event of sudden deceleration
(ie, an accident) an inertia switch cuts off the
power to the pump, so that the risk of fire
from fuel spraying out of broken fuel lines
under pressure is minimised.
The air metering system includes the inlet
air temperature control system and the air
cleaner, but the main components are in the
throttle body assembly. This incorporates the
injector (which sprays fuel onto the back of
the throttle disc), the throttle potentiometer
(which is linked to the throttle disc spindle,
and sends the ECU information on the rate of
throttle opening by transmitting a varying
voltage), and the stepper motor, (which is
controlled by the ECU, and operates the
throttle disc spindle lever via a cam and
pushrod to provide idle speed control).
The electrical control system consists of the
ECU, with all the sensors that provide it with
information, and the actuators by which it
controls the whole system’s operation. The
ECU’s manifold absolute pressure (MAP)
sensor is connected, by hoses and a fuel
(vapour) trap mounted on the bulkhead, to the
inlet manifold; variations in manifold pressure
are converted into graduated electrical
signals, which are used by the ECU to
determine the load on the engine. The inlet air
temperature sensor is self-explanatory; the
crankshaft sensor provides the engine speed
and crankshaft position; the coolant
temperature sensor supplies the engine
temperature, the accelerator pedal switch tells
the ECU when the accelerator is closed; the
throttle potentiometer is explained above, and
the function of the lambda sensor is explained
in Part C of this Chapter. The ECU also
senses battery voltage, and can adjust the
injector pulses width and use the stepper
motor to increase the idle speed and,
therefore, the alternator output it if is too low.
Short-circuit protection and diagnostic
capabilities are incorporated; the ECU can
both receive and transmit information via the
diagnostic connector, thus permitting engine
diagnosis and tuning by Rover diagnostic
equipment. If either the coolant temperature
sensor, the inlet air temperature sensor or the
manifold absolute pressure sensor circuits
should fail, the ECU has a back-up facility
which assumes a valve corresponding to a
coolant temperature of 60ºC, an inlet air
temperature of 35ºC and an engine load
based on the engine speed and throttle
position; these are used to implement a back-
up air/fuel mixture ratio.
All these signals are compared by the ECU,
using digital techniques, with set values pre-
programmed (mapped) into its memory.
Based on this information, the ECU selects
fuel and ignition settings appropriate to those
values, and controls the ignition HT coil
(varying the ignition timing as required), the
fuel injector (varying its pulse width - the
length of time the injector is held open - to
provide a richer or weaker mixture, as
appropriate), the stepper motor (controlling
the idle and fast idle speeds), the fuel pump
relay (controlling the fuel delivery), the
manifold heater relay (controlling the inlet
manifold pre-heater system) and the main
relay, the purge control valve, and the lambda
sensor and relay, accordingly. The mixture,
idle speed and ignition timing are constantly
varied by the ECU to provide the best settings
for cranking, starting and engine warm-up
(with either a hot or cold engine), idle,
cruising, and acceleration. A rev-limiter circuit
is built into the ECU, which switches off the
injector earth (ie, the fuel supply) if the engine
speed exceeds the recommended limit. The
injector earth is also switched off on the
overrun, to improve fuel economy and reduce
exhaust emissions.
The ECU idle control is an adaptive system;
it learns the engine load and wear
characteristics over a period of time, and
adjusts the idle speed to suit. If the ECU is
renewed, or one from another car is fitted, it
will take a short period of normal driving for
the new ECU to learn the engine’s
characteristics and restore full idle control.
Precautions
Warning: Petrol is extremely
flammable - great care must be
taken when working on any part
of the fuel system. Do not smoke
or allow any naked flames or uncovered
light bulbs near the work area. Note that
gas powered domestic appliances with
pilot flames, such as heaters, boilers and
tumble dryers, also present a fire hazard -
bear this in mind if you are working in an
area where such appliances are present.
Always keep a suitable fire extinguisher
close to the work area and familiarise
yourself with its operation before starting
work. Wear eye protection when working
on fuel systems and wash off any fuel spilt
on bare skin immediately with soap and
water. Note that fuel vapour is just as
dangerous as liquid fuel; a vessel that has
just been emptied of liquid fuel will still
contain vapour and can be potentially
explosive. Petrol is a highly dangerous and
volatile liquid, and the precautions
necessary when handling it cannot be
overstressed.
Many of the operations described in this
Chapter involve the disconnection of fuel
lines, which may cause an amount of fuel
spillage. Before commencing work, refer to
the above Warning and the information in
“Safety first” at the beginning of this
manual.
When working with fuel system
components, pay particular attention to
cleanliness - dirt entering the fuel system
may cause blockages which will lead to
poor running.
Note: Residual pressure will remain in the fuel
lines long after the vehicle was last used,
when disconnecting any fuel line, it will be
necessary to depressurise the fuel system as
described in Section 6.
2 Air cleaner assembly -
removal and refitting
1
Removal
1 Slacken and remove the three screws
securing the air cleaner assembly to the
throttle body (see illustration).
4B•2 Fuel system - fuel injection engines
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