Range Rover. Manual - part 63

EMISSION CONTROL

DESCRIPTION AND OPERATION

1. Vacuum reservoir
2. SAI vacuum solenoid valve
3. Engine Control Module (ECM)
4. Fuse 26 - Engine Compartment Fusebox
5. Main relay - Engine Compartment Fusebox
6. SAI pump relay - Engine Compartment Fusebox
7. Fuselink 2 - Engine Compartment Fusebox
8. Secondary Air Injection (SAI) pump
9. SAI control valves (2 off)

EMISSION CONTROL

NEW RANGE ROVER

DESCRIPTION AND OPERATION

Secondary air injection system - description

The secondary air injection (SAI) system comprises
the following components:

•

Secondary air injection pump

•

SAI vacuum solenoid valve

•

SAI control valves (2 off, 1 for each bank of
cylinders)

•

SAI pump relay

•

Vacuum reservoir

•

Vacuum harness and pipes

The SAI system is used to limit the emission of carbon
monoxide (CO) and hydrocarbons (HCs) that are
prevalent in the exhaust during cold starting of a spark
ignition engine.

The concentration of hydrocarbons experienced
during cold starting at low temperatures are
particularly high until the engine and catalytic
converter reach normal operating temperature. The
lower the cold start temperature, the greater the
prevalence of hydrocarbons emitted from the engine.

There are several reasons for the increase of HC
emissions at low cold start temperatures, including the
tendancy for fuel to be deposited on the cylinder walls,
which is then displaced during the piston cycle and
expunged during the exhaust stroke. As the engine
warms up through operation, the cylinder walls no
longer retain a film of fuel and most of the
hydrocarbons will be burnt off during the combustion
process.

The SAI pump is used to provide a supply of air into
the exhaust ports in the cylinder head, onto the back
of the exhaust valves, during the cold start period. The
hot unburnt fuel particles leaving the combustion
chamber mix with the air injected into the exhaust
ports and immediately combust. This subsequent
combustion of the unburnt and partially burnt CO and
HC particles help to reduce the emission of these
pollutants from the exhaust system. The additional
heat generated in the exhaust manifold also provides
rapid heating of the exhaust system catalytic
converters. The additional oxygen which is delivered
to the catalytic converters also generate an
exothermic reaction which causes the catalytic
converters to ’light off’ quickly.

The catalytic converters only start to provide effective
treatment of emission pollutants when they reach an
operating temperature of approximately 250

(482

F) and need to be between temperatures of

400

C (752

F) and 800

C (1472

F) for optimum

efficiency. Consequently, the heat produced by the
secondary air injection "afterburning", reduces the
time delay before the catalysts reach an efficient
operating temperature.

The engine control module (ECM) checks the engine
coolant temperature when the engine is started, and if
it is below 55

C (131

F), the SAI pump is started.

Secondary air injection will remain operational for a
period controlled by the ECM and is dependent on the
starting temperature of the engine. This varies from
approximately 95 seconds for a start temperature of
8

C (46

F) to 30 seconds for a start temperature of

C (131

F). The SAI pump operation can be cut

short due to excessive engine speed or load.

Air from the SAI pump is supplied to the SAI control
valves via pipework and an intermediate T-piece
which splits the air flow evenly to each bank.

At the same time the SAI pump is started, the ECM
operates a SAI vacuum solenoid valve, which opens
to allow vacuum from the vacuum reservoir to be
applied to the vacuum operated SAI control valves on
each side of the engine. When the vacuum is applied
to the SAI control valves, they open simultaneously to
allow the air from the SAI pump through to the
exhaust ports. Secondary air is injected into the inner
most exhaust ports on each bank.

When the ECM breaks the ground circuit to
de-energise the SAI vacuum solenoid valve, the
vacuum supply to the SAI control valves is cut off and
the valves close to prevent further air being injected
into the exhaust manifold. At the same time as the SAI
vacuum solenoid valve is closed, the ECM opens the
ground circuit to the SAI pump relay, to stop the SAI
pump.

A vacuum reservoir is included in the vacuum line
between the intake manifold and the SAI vacuum
solenoid valve. This prevents changes in vacuum
pressure from the intake manifold being passed on to
cause fluctuations of the SAI vacuum solenoid valve.
The vacuum reservoir contains a one way valve and
ensures a constant vacuum is available for the SAI
solenoid valve operation. This is particularly important
when the vehicle is at high altitude.

EMISSION CONTROL

DESCRIPTION AND OPERATION

Secondary air injection system - operation

When the engine is started, the engine control module
(ECM) checks the engine coolant temperature and if it
is below 55

C (131

F), the ECM grounds the electrical

connection to the coil of the SAI pump relay.

The Main and Secondary Air Injection (SAI) pump
relays are located in the engine compartment fusebox.
A 12V battery supply is fed to the contacts of the SAI
pump relay via fuselink 2. When the ECM completes
the earth path, the coil energises and closes the
contacts of the SAI pump relay to supply 12V to the
SAI pump. The SAI pump starts to operate, and will
continue to do so until the ECM switches off the earth
connection to the coil of the SAI pump relay.

An earth connection from the Main relay coil is
connected to the ECM. When the ECM completes the
earth path, the coil energises and closes the contacts
of the Main relay. When the contacts of the Main relay
are closed, a 12V battery supply is fed to the SAI
vacuum solenoid valve via fuse 26 in the engine
compartment fusebox. The ECM grounds the
electrical connection to the SAI vacuum solenoid
valve at the same time as it switches on the SAI pump
motor.

The SAI pump remains operational for a period
determined by the ECM and depends on the starting
temperature of the engine, or for a maximum
operation period determined by the ECM if the target
engine coolant temperature has not been reached in
the usual time.

When the SAI vacuum solenoid valve is energised, a
vacuum is provided to the operation control ports on
both of the vacuum operated SAI control valves at the
exhaust manifolds. The control vacuum is sourced
from the intake manifold depression and routed to the
SAI control valves via a vacuum reservoir and the SAI
vacuum solenoid valve.

The vacuum reservoir is included in the vacuum
supply circuit to prevent vacuum fluctuations caused
by changes in the intake manifold depression affecting
the smooth operation of the SAI control valves.

When a vacuum is applied to the control ports of the
SAI control valves, the valves open to allow
pressurised air from the SAI pump to pass through to
the exhaust ports in the cylinder heads for
combustion.

When the ECM has determined that the SAI pump
has operated for the desired duration, it switches off
the earth paths to the SAI pump relay and the SAI
vacuum solenoid valve. With the SAI vacuum solenoid
valve de-energised, the valve closes, cutting off the
vacuum supply to the SAI control valves. The SAI
control valves close immediately and completely to
prevent any further pressurised air from the SAI pump
entering the exhaust manifolds.

The engine coolant temperature sensor incurs a time
lag in respect of detecting a change in temperature
and the SAI pump automatically enters a ’soak period’
between operations to prevent the SAI pump
overheating. The ECM also compares the switch off
and start up temperatures, to determine whether it is
necessary to operate the SAI pump. This prevents the
pump running repeatedly and overheating on repeat
starts.

Other factors which may prevent or stop SAI pump
operation include the prevailing engine speed/load
conditions.

EMISSION CONTROL

NEW RANGE ROVER

DESCRIPTION AND OPERATION

Evaporative emission control system - pre
advanced EVAPS.

The system is designed to prevent harmful fuel vapour
escaping to the atmosphere. The system comprises a
vapour separator (C) and a two way valve (D), both
located on the fuel filler neck (A), an Evaporative
Emissions (EVAP) canister and an EVAP canister
purge valve.

Fuel filler neck

External fill breather pipe

Fuel/vapour separator

Two way valve - fuel vapour to EVAP canister

Fuel vapour from fuel tank

During conditions of high ambient temperatures, fuel
in the tank vapourises, and pressure rises. Fuel
vapour enters the vapour separator and any liquid fuel
runs back to the tank. Three roll over valves (ROVs)
are fitted in the fuel tank vapour lines. These valves
prevent liquid fuel entering the vapour separator if the
vehicle rolls over. When pressure rises above 5 to 7
kPa (0.7 to 1.0 lbf/in

), the two way valve opens and

allows fuel vapour to flow to the EVAP canister where
it is stored in the canister’s activated charcoal
element. When the correct engine operating
conditions are met, the Engine Control Module (ECM)
opens the EVAP canister purge valve and vapour is
drawn from the canister, into the plenum chamber to
be burned in the engine. Fresh air is drawn into the
canister through a vent to take up the volume of
displaced vapour. If the two way valve should fail, or
the main vapour line becomes blocked, excess
pressure is vented to atmosphere through a valve in
the fuel filler cap. Similarly, the cap vent valve will
open to prevent the tank collapsing if excessive
vacuum is present.

When the temperature of fuel in the tank reduces,
pressure also reduces and vapour must be drawn
back into the tank. When tank pressure drops into
vacuum, the two way valve opens, allowing fuel
vapour to be drawn out of the EVAP canister into the
fuel tank. Again, fresh air is drawn into the canister to
take up the displaced volume.

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