Discovery 2. Manual — part 59

EMISSION CONTROL - V8

DESCRIPTION AND OPERATION 17-2-31

SAI Control Valves

1 Pressurised air from SAI pump
2 Vacuum operated SAI control valve
3 Vacuum hose from SAI vacuum solenoid valve

4 Pressurised air to exhaust manifold
5 Protective heat sleeving
6 Air delivery pipe to exhaust manifold

The SAI control valves are located on brackets at each side of the engine.

The air injection supply pipes connect to a large bore port on the side of each SAI control valve via a short rubber
connection hose. A small bore vacuum port is located on each SAI control valve at the opposite side to the air injection
supply port. The vacuum supply to each vacuum operated SAI control valve is through small bore nylon hoses from
the SAI vacuum solenoid valve. An intermediate connector is included in the vacuum supply line to split the vacuum
applied to each vacuum operated valve, so that both valves open and close simultaneously.

When a vacuum is applied to the SAI control valves, the valve opens to allow the pressurised air from the SAI pump
through to the exhaust manifolds. The injection air is output from each SAI control valve through a port in the bottom
of each unit. A metal pipe connects between the output port of each SAI control valve and each exhaust manifold via
an intermediate T-piece. The T-piece splits the pressurised air delivered to ports at the outer side of the two centre
exhaust ports on each cylinder head. The pipes between the T-piece and the exhaust manifold are enclosed in
thermal sleeving to protect the surrounding components from the very high heat of the exhaust gas, particularly at
high engine speeds and loads.

When the SAI vacuum solenoid valve is de-energised, the vacuum supply line opens to atmosphere, this causes the
vacuum operated valves to close automatically and completely to prevent further air injection.

As a result of SAI control valve malfunction, certain fault codes may be stored in the ECM diagnostic memory, which
can be retrieved using Testbook/T4. These may include the following::

M17 0205

1

3

4

4

2

6

5

EMISSION CONTROL - V8

17-2-32 DESCRIPTION AND OPERATION

NOTE: Refer to 'SAI System Fault Finding' and 'Checking Malfunctions on SAI System' at the end of the 'Secondary
Air Injection System Operation' section to determine root cause of fault codes.

The system diagnostics monitor the whole SAI system for correct operation. Malfunction of any one of the SAI
components can cause the above fault codes to be stored.

Therefore, correct fault finding methods and investigation are essential to determine the root cause of the fault
code(s). TestBook/T4 must be used to perform active SAI diagnostics.

P-code

Description

P1412

Secondary Air Injection System – Malfunction Bank 1 LH (Insufficient SAI flow
during passive test)

P1413

Secondary Air Injection System – Air control valve always open Bank 1 LH
(Excessive SAI flow during active leak test)

P1414

Secondary Air Injection System – Malfunction Bank 1 LH (Insufficient SAI flow
during passive test)

P1415

Secondary Air Injection System – Malfunction Bank 2 RH (Insufficient SAI flow
during passive test)

P1416

Secondary Air Injection System – Ait control valve always open Bank 2 RH
(Excessive SAI flow during active leak test)

P1417

Secondary Air Injection System – Low air flow Bank 2 RH (Insufficient SAI flow
during active test)

EMISSION CONTROL - V8

DESCRIPTION AND OPERATION 17-2-33

Vacuum Reservoir

1 Vacuum port to SAI vacuum solenoid valve
2 Vacuum port to intake manifold

(one-way valve end)

3 Vacuum reservoir

A vacuum reservoir is included in the vacuum supply line between the intake manifold and the SAI vacuum solenoid
valve. The vacuum reservoir contains a one-way valve, to stop depression leaking back towards the intake manifold
side. The reservoir holds a constant vacuum so that the SAI control valves open instantaneously as soon as the SAI
solenoid valve is energised.

The vacuum reservoir is a plastic canister construction located on a bracket at the LH side of the engine compartment
on vehicles up to 2003 model year and on the RH side of the engine compartment, near the bulkhead, on vehicles
from 2003 model year. It is important to ensure the reservoir is fitted in the correct orientation, and the correct vacuum
hoses are attached to their corresponding ports. The one-way valve end of the vacuum reservoir (cap end, to inlet
manifold) is fitted towards the rear of the vehicle.

A small bore nylon hose is used to connect the one-way valve end of the vacuum reservoir to a port on the RH side
of the inlet manifold. A further hose connects between the other port on the vacuum reservoir and a port on the front
of the SAI vacuum solenoid valve.

M17 0212

1

2

3

EMISSION CONTROL - V8

17-2-34 DESCRIPTION AND OPERATION

Crankcase Emission Control Operation

Oil laden noxious gas in the engine crankcase is drawn through a spiral oil separator located in the stub pipe to the
ventilation hose on the right hand cylinder head rocker cover, where oil is separated and returned to the cylinder head.
The rubber ventilation hose from the right hand rocker cover is routed to a port on the right hand side of the inlet
manifold plenum chamber, where the returned gases mix with the fresh inlet air passing through the throttle butterfly
valve. The stub pipe on the left hand rocker cover does not contain an oil separator, and the ventilation hose is routed
to the throttle body housing at the air inlet side of the butterfly valve. The mass of fresh air which is drawn in from the
atmospheric side of the throttle butterfly to mix with the returned crankcase gas depends on the throttle position and
the engine speed.

1 Hose – RH rocker cover to inlet manifold
2 Inlet manifold
3 Throttle body
4 Air intake
5 Hose – LH rocker cover to inlet manifold
6 LH rocker cover breather tube

(without oil separator)

7 LH rocker cover baffle
8 RH rocker cover baffle
9 RH rocker cover breather tube

10 Oil separator (integral with breather tube)

When the engine is running in cruise conditions or at idle, manifold pressure is low and the majority of gases are drawn
into the inlet manifold through the oil / vapour separator in the RH rocker cover stub pipe. At the same time, filtered
air is drawn from the throttle body into the engine via the LH rocker cover.

During periods of driving at Wide Open Throttle (WOT), pressure at either side of the throttle disc equalizes (manifold
depression collapses). The larger ventilation opening at the throttle housing positioned in the fast moving stream of
intake air, now offers more 'pull' than the small opening in the RH rocker cover and the flow of ventilation reverses,
drawing gases from the LH rocker cover into the throttle body for subsequent burning in the combustion chambers.