1 General information andprecautions
General information
The fuel system consists of a fuel tank
(mounted under the body, beneath the rear
seats), fuel hoses, an electric fuel pump
mounted in the fuel tank, and a central fuel
injection (CFi) system. Fuel is supplied from the tank by an integral
electric fuel pump (and combined fuel gauge
sender unit). The fuel is passed through an in-
line filter within the engine compartment, then
to the fuel injection unit. The fuel is maintained
at the required operating pressure by a
pressure regulator unit. The CFi unit itself is a relatively simple
device when compared with a conventional
carburettor. Fuel is injected by a single
solenoid valve (fuel injector) which is mounted
centrally on top of the unit. It is this feature
which gives the system CFi (or Central Fuel
injection) its name (see illustration).The injector is energised by an electrical
signal sent from the EEC IV engine
management module. When energised, the
injector pintle is lifted from its seat, and
atomised fuel is delivered into the inlet
manifold under pressure. The electrical
signals take two forms of current - a high
current to open the injector, and a low current
to hold it open for the duration required. At
idle speed, the injector is pulsed at every
other inlet stroke, rather than with every
stroke as during normal operation.
The air-to-fuel mixture ratio is regulated by
the EEC IV module, based on inputs from the
various engine sensors. No adjustments to
the fuel mixture are possible.
The throttle plate control motor (mounted
on the side of the CFi unit) regulates the idle
speed by reacting to the signals sent by the
EEC IV module. The signals are calculated by
the values and information provided from the
engine sensors. When the throttle position
sensor indicates that the throttle is closed, the
module enters the idle speed mode or
dashpot mode (according to engine speed).
The module maintains the idle speed at a constant value, making minor adjustments as
necessary for different loads and conditions.
The base idle speed can only be adjusted by a
dealer or fuel injection specialist with the
necessary equipment to link up to the engine
management module.
To prevent the engine from running on (or
dieseling) when it is switched off, the EEC IV
module sends a signal to the throttle plate
control motor, to fully close the throttle plate
and return it to its preset position ready for
restarting. When the ignition is switched on
to restart the engine, the motor repositions
the throttle plate to the position required
according to the prevailing conditions. The EEC IV module is the heart of the entire
engine management system, controlling the
fuel injection, ignition and emissions control
systems. The module receives information
from various sensors to determine engine
temperature, speed and load, and the
quantity of air entering the engine. The
sensors also inform the module of throttle
position, inlet air temperature and exhaust gas
oxygen content. All the information supplied
to the module is computed and compared
with pre-set values stored in it’s memory, to
determine the required period of injection. Information on crankshaft position and
engine speed is generated by the distributor
on pre-1990 CVH engine models, or by a
crankshaft position sensor on all other
models. The inductive head of the crankshaft
position sensor runs just above the engine
flywheel and scans a series of 36 protrusions
on the flywheel periphery. As the crankshaft
rotates, the sensor transmits a pulse to the
system’s ignition module every time a
protrusion passes it. There is one missing
protrusion in the flywheel periphery at a point
corresponding to 90º BTDC. The ignition
module recognises the absence of a pulse
from the crankshaft position sensor at this
point to establish a reference mark for
crankshaft position. Similarly, the time interval
between absent pulses is used to determine
engine speed. This information is then fed to
the EEC IV module for further processing. Engine temperature information is supplied
by the coolant temperature sensor. This
component is an NTC (Negative Temperature
Coefficient) thermistor - that is, a semi-
conductor whose electrical resistance
decreases as its temperature increases. It
provides the EEC IV module with a constantly-
varying (analogue) voltage signal,
corresponding to the temperature of the
engine coolant. This is used to refine the
calculations made by the module, when
determining the correct amount of fuel
required to achieve the ideal air/fuel mixture
ratio. Inlet air temperature information is supplied
by the inlet air temperature sensor. This
component is also an NTC thermistor - see
the previous paragraph - providing the EEC IV
module with a signal corresponding to the
temperature of air passing into the engine.
4B•2 Fuel system - central fuel injection engines
1.3 Exploded view of the CFi unit
1 Fuel injector assembly
2 Fuel pressure regulator
assembly 3 Fuel feed connector
4 Intake air temperature
sensor 5 Throttle-plate control
motor
6 Throttle position sensor
7 Fuel injector wiring
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