Discovery 2. Manual - part 472

ENGINE MANAGEMENT SYSTEM - TD5

DESCRIPTION AND OPERATION 18-1-31

The purpose of the glow plugs is:

Assist cold engine start.

Reduce exhaust emissions at low engine load/speed.

The main part of the glow plug is a tubular heating element that protrudes into the combustion chamber of the engine.
The heating element contains a spiral filament that is encased in magnesium oxide powder. At the tip of the tubular
heating element is the heater coil. Behind the heater coil and connected in series is a control coil. The control coil
regulates the heater coil to ensure that it does not overheat and cause a possible failure. The glow plug circuit has its
own control relay located in the engine compartment fuse box.

Pre-heat is the length of time the glow plugs operate prior to engine cranking. The ECM controls the pre-heat time of
the glow plugs based on battery voltage and coolant temperature information via the glow plug relay.

Post-heat is the length of time the glow plugs operate after the engine starts. The ECM controls the post-heat time
based on ECT information. If the ECT fails the ECM will operate pre/post-heat time strategies with default values from
its memory. The engine will be difficult to start.

Input/Output
The glow plugs receive voltage from the glow plug relay that is controlled by the ECM. The ECM provides the earth
path for the relay coil closing the relay contacts and supplying the glow plugs with battery voltage. The supply voltage
heats the coils to approximately 1000

C (1832

F). The glow plug circuit is wired in parallel, the body of each glow

plug is screwed directly into the engine block which provides each glow plug with an earth path.

The glow plugs can fail in the following ways:

Heater coil open circuit.

Control coil open circuit.

Poor earth quality.

Short circuit to vehicle supply.

Short circuit to vehicle earth.

Wiring loom fault.

Relay windings open circuit.

Incorrect relay fitted.

In the event of a glow plug failure any of the following symptoms may be observed:

Difficult starting.

Excessive smoke emissions after engine start.

ENGINE MANAGEMENT SYSTEM - TD5

18-1-32 DESCRIPTION AND OPERATION

Turbocharger

1 Exhaust gas from manifold
2 Studs to exhaust manifold
3 Turbocharger cast iron housing
4 Wastegate valve linkage
5 Exhaust gas out to front exhaust pipe
6 Compressed intake air
7 Fresh intake air
8 Turbocharger aluminium alloy housing
9 Wastegate valve vacuum port

The Td5 engine utilises a Garrett GT20 turbocharger with an electronically controlled wastegate modulator to improve
engine performance. The turbocharger uses the engine's exhaust gas to spin a turbine at very high speed. This
causes inlet air on the other side of the turbine to be drawn in through the turbocharger intake for compression. The
inlet air is carried round by the vanes of the compressor and then thrown out under centrifugal force from the
turbocharger's outlet duct. This compression of air enables a greater quantity of air to be delivered to the inlet manifold
via an intercooler. Combustion is improved through better volumetric efficiency. The use of a turbocharger improves
fuel consumption and increases engine torque and power. Exhaust noise is also reduced due to the smoothing out of
exhaust pulsations.

The rear cast iron body of the turbocharger housing connects to a port on the exhaust manifold at the LH side of the
cylinder head by three studs and nuts. The interface between the exhaust manifold and the turbocharger housing is
separated by a metal gasket. The exhaust outlet of the turbocharger is located at the bottom of the turbocharger cast
iron housing; it is connected to the exhaust system front downpipe and is attached by three studs and nuts. The
interface between the turbocharger housing and the exhaust front pipe is separated by a metal gasket.

The front casing of the turbocharger is constructed from aluminium alloy and is connected to the air inlet duct by a
metal band clip. The compressed air outlet is connected to the intercooler by a metal pipe which has rubber hose
extensions at each end attached by metal band clips.

ENGINE MANAGEMENT SYSTEM - TD5

DESCRIPTION AND OPERATION 18-1-33

The turbocharger is exposed to extremely high operating temperatures (up to 1,000

C (1832

F)) because of the hot

exhaust gases and the high speed revolution of the turbine (up to 150,000 rev/min). In order to resist wear of the
turbine bearings a flow of lubrication oil is supplied from the engine lubrication system to keep the bearings cool. Oil
is supplied from a tapping at the front of the full-flow filter adaptor housing via a metal pipe with banjo connections.
Oil is returned to the sump via a metal pipe which connects to the cylinder block at a port below the turbocharger
assembly.

A heatshield is attached to the left hand side of the engine to protect adjacent components from the heat generated
at the turbocharger. The heatshield is attached to the engine by two bolts an additional bolt attaches the heatshield
to the turbocharger casting.

The engine control module controls the amount of boost pressure the engine receives by way of the turbocharger.
When full boost is reached a control signal is sent to the wastegate modulator, and a vacuum is applied to the
wastegate valve. The wastegate valve opens, bypassing some of the exhaust gas away from the turbine to be output
to the exhaust system.

The engine should be allowed to idle for 15 seconds following engine start up and before the engine is switched off
to protect the turbocharger by maintaining oil supply to the turbine bearings.

Intercooler
The intercooler is an air-to-air heat exchanger which lowers the intake air temperature to obtain a higher air density
for better combustion efficiency. The intercooler receives compressed air from the turbocharger via a metal pipe; it
cools the intake air via the intercooler matrix and delivers it to the intake manifold by means of a rubber hose which
connects between the intercooler outlet and the intake manifold outlet. The rubber hose is connected to ports at each
end by metal band clips.

COOLING SYSTEM - Td5, DESCRIPTION AND OPERATION, Description.

The intercooler is located at the front of the engine bay, forward of the radiator.

ENGINE MANAGEMENT SYSTEM - TD5

18-1-34 DESCRIPTION AND OPERATION

Turbocharger wastegate modulator

The turbocharger wastegate modulator is located on the ancillary bracket on the engine, and is connected by flexible
pipes to the turbocharger. The modulator controls turbocharger boost pressure by varying the pressure used to open
the turbocharger wastegate. This control is vital to ensure the turbocharger does not over boost the engine.

Input/Output
The turbocharger wastegate modulator receives battery voltage from the main relay. The ECM supplies the earth path
in the form of a pulse width modulated (PWM) signal. The PWM signal from the ECM operates the modulator at a
frequency of less than 50 Hz. This signal allows the turbocharger wastegate modulator to open and close the
wastegate. This permits a proportion of the exhaust gas to bypass the turbocharger through the wastegate, thereby
regulating boost pressure.

Input voltage to the turbocharger wastegate modulator is via the main relay.

The earth path is via a PWM signal generated at pin 21 of the ECM connector C0158.

The turbocharger wastegate modulator can fail as follows:

Open circuit.

Short circuit to voltage supply.

Short circuit to vehicle earth.

Wiring loom fault.

Connector water ingress.

Connector failure due to excess heat.

Component failure due to excess heat.

Component failure due to excess vibration.

In the event of a turbocharger wastegate modulator failure any of the following symptoms may be observed:

Reduced engine performance.

Increased engine performance.

Lack of power.

Excess smoke.

Reduced fuel economy.

The MIL will not illuminate in the event of a turbocharger wastegate modulator failure.

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