Discovery 2. Manual — part 449

EMISSION CONTROL - TD5

DESCRIPTION AND OPERATION 17-1-11

EU3 models: The exhaust gases are routed from the exhaust manifold through the EGR cooler to the underside of
the EGR valve. The EGR cooler is bolted to the front of the engine cylinder head. An EGR pipe connects the EGR
cooler to the exhaust manifold and is secured by two Allen screws. The two Allen screws fixing the EGR pipe to the
exhaust manifold should be replaced every time the EGR pipe is removed. A second pipe connects the EGR cooler
to the EGR valve; this pipe is secured to the EGR valve by a clip, and to the cooler by two Allen screws.Extreme care
should be exercised when removing and refitting the EGR pipe to avoid damage. When refitting the EGR
cooler, always tighten the pipe connections BEFORE tightening the bolts securing the cooler to the cylinder
head.

When a vacuum is applied to the EGR suction port, it causes a spindle with sealing disc (EGR valve) to be raised,
opening the port at the EGR pipe to allow the recirculated exhaust gas to pass through into the inlet manifold. The
valve is spring loaded so that when the vacuum is removed from the suction port, the valve returns to its rest position
to tightly close the exhaust gas port.

A vacuum is simultaneously applied to the inlet throttle (ILT) valve suction port which causes the butterfly valve in the
inlet manifold to close by means of a spindle and lever mechanism. Closing the butterfly valve limits the supply of
fresh intercooled air entering the inlet manifold and causes a depression within the inlet manifold to create a greater
suction at the open port to the EGR delivery pipe. In this condition a greater mass of recirculated exhaust gas is drawn
into the inlet manifold for use in the combustion process. When the vacuum is released from the ILT valve suction port
a spring returns the butterfly valve to its fully open position.

By controlling the quantities of recirculated exhaust gas and fresh intake air available in the inlet manifold, the
optimum mix for the prevailing engine operating conditions can be maintained which ensures the intake gas to the
combustion chambers will have burning rate properties which will reduce the NO

x

emissions to an acceptable level.

Normally, full recirculation is only applicable when the NO

x

emissions are most prevalent.

EMISSION CONTROL - TD5

17-1-12 DESCRIPTION AND OPERATION

EMISSION CONTROL - TD5

REPAIRS 17-1-13

REPAIRS

Modulator - EGR

$% 17.45.04

There are two types of modulator fitted. System type
1 has a single modulator, and type 2 has a second
modulator (ILT modulator) bolted to the same
mounting plate.

Remove

1. Disconnect vacuum pipe(s) and multiplug(s)

from EGR modulator.

2. Remove 2 nuts and remove EGR modulator.

Refit

1. Position EGR modulator and tighten securing

nuts.

2. Connect vacuum hose(s) and multiplug(s).

Inlet Throttle (ILT) Modulator

$% 17.45.03

Remove

1. Identify the fitted positions of the 3 vacuum

pipes, then disconnect from the ILT modulator
valve.

2. Disconnect multiplug from ILT modulator.
3. Remove 2 nuts securing modulator and remove

ILT modulator from its mountings.

Refit

1. Fit ILT modulator to its mountings, fit the nuts

and tighten to 10 Nm (7 lbf.ft).

2. Connect vacuum pipes to the positions

identified during removal.

3. Connect multiplug to ILT modulator.

EMISSION CONTROL - TD5

17-1-14 REPAIRS

Valve - EGR - Pre EU3 models

$% 17.45.01

On all vehicles up to VIN number 1A736339, the
EGR pipe assembly must be replaced every time the
system is disturbed.

Remove

1. Release turnbuckles and remove battery cover.
2. Disconnect battery earth lead.
3. Remove 3 bolts and remove engine acoustic

cover.

4. Remove cooling fan coupling.

+

COOLING SYSTEM - Td5, REPAIRS,

Fan - viscous.

5. Disconnect vacuum hose(s) from EGR valve.
6. Loosen clip and release air intake from EGR

valve.

7. Remove 4 bolts, release EGR valve from inlet

manifold and discard gasket.

8. Remove 2 bolts and release EGR valve clip

from cylinder head.

9. Remove and discard 2 bolts securing EGR

valve pipe to exhaust manifold.

10. Remove EGR valve assembly.
11. Remove clip and remove pipe from EGR valve.

Refit

1. Clean EGR valve and mating face on pipe.
2. Position pipe to EGR valve and fit retaining clip.

Fit bolt but do not tighten at this stage.

3. Position EGR valve assembly, locate pipe

flange to exhaust manifold, fit new bolts but do
not tighten at this stage.

4. Clean inlet manifold and EGR valve mating

faces.

5. Using new gasket, position EGR valve to inlet

manifold fit bolts and tighten to 10 Nm (7 lbf.ft).

6. Align EGR pipe clip to cylinder head, fit bolts

but do not tighten at this stage.

7. Tighten EGR pipe bolts to correct torque in

following sequence:

l

EGR pipe retaining clip bolt 6 Nm (4.5 lbf.ft)

l

EGR pipe clip to cylinder head bolts 10 Nm
(7 lbf.ft)

l

EGR pipe flange to exhaust manifold bolts
10 Nm (7 lbf.ft)

8. Position air intake hose and tighten clip.
9. Connect vacuum hoses to EGR valve.

10. Fit cooling fan coupling.

+

COOLING SYSTEM - Td5, REPAIRS,

Fan - viscous.

11. Connect battery earth lead.
12. Fit battery cover and secure the fixings.