System Actuators - Triumph Tiger Service Manual

9 FUEL SYSTEM/ENGINE MANAGEMENT
System Actuators
In response to signals received from the sensors, the
ECM directs messages to a series of electronic and
electro-mechanical actuators. The function and location
of the actuators is given below.
•
Idle Air Control System - located inside the
airbox. The system comprises an air control valve
fitted with a. stepper motor. The system has a
controlling influence over the following:
• Idling.
• Induction air supply during engine overrun.
• Air/fuel ratio correction when operating at
altitudes above sea level.
• Cold and hot start air/fuel ratio correction.
When in operation, the stepper motor opens the air
control valve by a variable distance, allowing a
controlled supply of air to flow along a series of
pipes, into the induction system. The air is fed to a
point between the throttle plates and the inlet
valves.
Idling • When the engine is idling, the stepper
motor opens the idle air control valve allowing air to
be fed to the engine even though the throttles are
closed. The distance that the idle air control valve is
opened is controlled by the ECM using information
received from the coolant temperature sensor,
barometric pressure sensor etc. Idle air fuel ratio is
adjusted by feeding more or less air to mix with the
fuel supplied by the injectors.
Overrun • During overrun conditions, where air
flow into the cylinder is very low, the idle air control
system feeds additional air to the induction system
allowin,g normal air/fuel ratios to be maintained.
Without the additional air flow, incomplete
combustion may take place which could cause
unburnt fuel to collect in the exhaust system
resulting in backfiring when the throttle is
re-opened.
Altitude correction· If the vehicle is operated at
high altitude, the reduced air density will be
compensated for by varying the amount of air fed to
the engine via the idle air control system. For
example, at high altitudes, the idle air control
system feeds a greater volume of air to the induction
system to compensate for the air's reduced oxygen
content.
Cold and hot start· Except in very cold conditions
where a small amount of throttle opening aids cold
start performance, the engine is usually started with
the throttle in the closed position. The idle air
control system regulates the start-up air supply to
the induction system.
9.12
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Canister purge valve (California models only) -
situated in the vapour return line between the
carbon canister and the throttle. The purge valve
controls the return of vapour which has been stored
in the carbon banister during the period when the
engine is switched off. The valve is 'pulsed' by the
ECM .to give control over the rate at which the
canister is purged. If the valve was not pulsed, all
the stored vapour would immediately be drawn into
the engine briefly causing a rich mixture and very
high emissions.
Injectors - located in the throttle body assembly.
The engine is fitted with 3 twin-jet injectors which
are targeted as close as possible to the back face of
the inlet valves. The spray pattern of the injectors is
fixed but the length of time each injector remains
open is variable. The duration of each injection is
calculated by the ECM using data received from the
various sensors in the system.
Plug top ignition coils - mounted directly onto the
top of each spark plug. The ECM controls the point
at which the coils are switched on and off. In
calculating the switch-on time, the ECM allows
sufficient time for the coils to charge to a level where
a spark can be produced. The coils are switched off
at the point of ignition, the timing of which is
optimised for good engine performance.
Main power relay .. situated adjacent to the ECM,
beneath the motorcycle seat. When the ignition is
switched on, the main power relay is powered up to
provide a stable voltage supply for the ECM.
When the ignition is switched off, the ECM holds the
main power relay on so that it can carry out the
power down procedure which includes;
•
writing data to the ECM memory,
•
referencing the position of the idle air control
valve stepper motor,
•
running the cooling fan until the engine is
suffiCiently cool.
Once all the power down procedures have been
carried out, the main power relay is turned off.
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