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4C•2 Emissions control systems
2.3 Disconnect the charcoal canister
quick-release connectors
fuel mixture accordingly by altering the fuel
injector pulse width.
Fuel evaporation emission control
9 To minimise the escape into the atmosphere
of unburned hydrocarbons, a fuel evaporation
emission control system is fitted. The fuel tank
filler cap is sealed and a charcoal canister is
mounted behind the right-hand front wing.
The canister collects the petrol vapours
generated in the tank when the car is parked
and stores them until they can be cleared from
the canister (under the control of the engine
management system ECU) via the purge valve
into the intake manifold to be burned by the
engine during normal combustion.
10 To ensure that the engine runs correctly when
it is cold and/or idling and to protect the catalytic
converter from the effects of an over-rich mixture,
the purge control valve is not opened by the ECU
until the engine has warmed-up, and the engine is
under load; the valve solenoid is then modulated
on and off to allow the stored vapour to pass into
the intake manifold.
Exhaust gas recirculation system
11 This system is designed to recirculate
small quantities of exhaust gas into the intake
manifold, and therefore into the combustion
process. This reduces the level of unburnt
hydrocarbons present in the exhaust gas before
it reaches the catalytic converter. The system
is controlled by the engine management ECU,
using the information from its various sensors,
via the electrically-operated EGR solenoid valve
mounted on a housing bolted to the left-hand
end of the cylinder head.
Diesel engines
Crankcase emission control
12 To reduce the emission of unburned
hydrocarbons from the crankcase into the
atmosphere, the engine is sealed and the
blow-by gases and oil vapour are drawn from
inside the crankcase, through an oil separator,
into the intake tract to be burned by the engine
during normal combustion.
13 Under all conditions the gases are forced
out of the crankcase by the (relatively} higher
crankcase pressure; if the engine is worn, the
raised crankcase pressure (due to increased
blow-by) will cause some of the flow to return
under all manifold conditions.
2. 7 Withdraw the canister, together with
the vapour hoses from the inner wing
Exhaust emission control
14 To minimise the level of exhaust pollutants
released into the atmosphere, a catalytic
converter and a diesel particulate filter are
fitted in the exhaust system.
15 The catalytic converter consists of a
canister containing a fine mesh impregnated
with a catalyst material, over which the hot
exhaust gases pass. The catalyst speeds up
the oxidation of harmful carbon monoxide,
unburned hydrocarbons, effectively reducing
the quantity of harmful products released into
the atmosphere via the exhaust gases.
16 The diesel particulate filter is incorporated
in the exhaust system intermediate pipe and
contains a silicon carbide honeycomb block
containing microscopic channels in which the
exhaust gases flow. As the gases flow through
the honeycomb channels, soot particles are
deposited on the channel walls. To prevent
clogging of the honeycomb channels, the soot
particles are burned off at regular intervals
during what is known as a 'regeneration
phase'. Under the control of the injection
system ECU, the injection characteristics
are altered to raise the temperature of the
exhaust gases to approximately 600°C.
At this temperature, the soot particles are
effectively burned off the honeycomb walls as
the exhaust gases pass through. A differential
pressure sensor and two temperature sensors
are used to inform the ECU of the condition of
the particulate filter, and the temperature of the
exhaust gases during the regeneration phase.
When the ECU detects that soot build-up is
reducing the efficiency of the particulate filter,
it will instigate the regeneration process.
This occurs at regular intervals under certain
driving conditions and will normally not be
detected by the driver.
Exhaust gas recirculation system
17 This system is designed to recirculate
small quantities of exhaust gas into the intake
tract, and therefore into the combustion
process. This process reduces the level of
unburnt hydrocarbons present in the exhaust
gas before it reaches the catalytic converter.
The system is controlled by the injection
system ECU, using the information from its
various sensors, via the electrically-operated
EGR valve.
2.9 Typical purge valve location (arrowed)
Crankcase emission control
1 The components of this system require no
attention other than to check that the hose(s)
are clear and undamaged at regular intervals.
Evaporative emission control
Testing
2 If the system is thought to be faulty,
disconnect the hoses from the charcoal
canister and purge control valve and check
that they are clear by blowing through them.
Full testing of the system can only be carried
out using specialist electronic equipment
which is connected to the engine management
system diagnostic wiring connector (see
Chapter 4A). If the purge control valve or
charcoal canister are thought to be faulty, they
must be renewed.
Charcoal canister renewal
3 At the right-hand rear corner of the engine
compartment, disconnect the quick-release
connectors connecting the charcoal canister
to the intake manifold and fuel vapour hose
(see illustration). A Vauxhall special tool
is available to release the connectors, but
provided care is taken, the connectors can be
released using a pair of long-nosed pliers, or a
similar tool, to depress the retaining tangs.
4 Apply the handbrake, then jack up the front
of the vehicle and support it on axle stands
(see Jacking and vehicle support). Remove
the right-hand front roadwheel.
5 Remove the wheel arch liner for access to
the charcoal canister which is located on the
inner wing.
6 Unbolt the charcoal canister from the
mounting bracket.
7 Withdraw the canister, together with the
vapour hoses from the inner wing (see
illustration).
8 Refitting is a reversal of the removal
procedure. Make sure the hoses are correctly
and securely reconnected.
Purge valve renewal
9 Disconnect the wiring from the purge
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