Defender 90 NAS. Instruction - page 19

17

EMISSION CONTROL

4

DESCRIPTION AND OPERATION

EVAPORATIVE EMISSION CONTROL SYSTEM

The system is designed to prevent harmful fuel vapour
from escaping to the atmosphere. The system
consists of a vapour separator tank, connected to the
fuel tank and located between the body inner and
outer panels on the right hand side of the vehicle near
the rear wheel arch. An Evaporative Emissions
(EVAP) canister, containing activated charcoal, is
positioned in the engine compartment attached to the
front right valance. The two components are
connected by a pipe running the length of the chassis.

A

Pressure relief to atmosphere.

B

From fuel tank to separator.

C

To evaporative emmissions canister.

D

Pressure relief valve.

E

Pressure relief valve.

F

Shut-off valve.

G

"Speed Fit" connectors.

A pressure relief valve is fitted in the hose which is
open to atmosphere. This valve acts as a safety valve
should a build-up of pressure occur in the system, for
example if a hose became blocked or kinked. The
volume of vapour emitted, in such an instance, would
be limited.

A pressure relief valve is also fitted in the hose
connected to the adsorption canister and releases
vapor to the canister when the pressure in the
separator reaches between 5 and 7 Kpa, 0.7 and 1.0
lbf/in

2

.

In the top of the separator a shut-off valve is
incorporated in the vapour exit port to prevent the
possible presence of any liquid fuel being transmitted
to the EVAP canister should the vehicle roll over.

The EVAP canister, which is connected by a hose to
the plenum chamber, absorbs and stores the fuel
vapour from the fuel tank while the engine is not
running. When the engine is started, the vapour is
purged from the canister by air drawn through an
orifice in the base of the canister and by the influence
of vacuum at the top. The vapour drawn into the
plenum chamber through a solenoid operated purge
valve is finally burnt in the combustion chambers.

The purge valve, which is attached to the evap
canister support bracket, is controlled by the Engine
Control Module ECM which determines the optimum
time at which purging should take place. This will
normally be at engine speeds above idle and when
the vehicle is in motion. A signal from the ECM to the
purge valve operates the solenoid and opens the
valve to purge the canister of fuel vapour.

EMISSION CONTROL

5

DESCRIPTION AND OPERATION

1. Vapour separator and pipes
2. Non-return valve to atmosphere
3. Pipe from fuel tank
4. Pipe to EVAP canister
5. EVAP canister and purge valve
6. Fuel tank

EMISSION CONTROL

1

FAULT DIAGNOSIS

TESTING EVAPORATIVE EMISSION CONTROL

Equipment required.

Nitrogen cylinder (compressed air may be used to
pressure the system when there has NEVER been
fuel present in the fuel or evaporative control
systems).

The following pressure test procedure is intended to
provide a method for ensuring that the system does
not leak excessively and will effectively control
evaporative emissions.

Water manometer (0 - 30" H2O or more).

Pipework and a "T" piece.

Method.

1. Ensure that there is at least two gallons of fuel in

the petrol tank unless there has never been any
fuel in the system.

2. Disconnect, at the EVAP canister, the pipe to the

vapour separator.

3. Connect this pipe to the nitrogen cylinder and

the water manometer using the "T" piece.

4. Pressurize the system to between 26.5 and 27.5

inches of water, allow the reading to stabilize,
then turn off the nitrogen supply.

5. Measure the pressure drop within a period of 2

minutes 30 seconds. If the drop is greater than
2.5 inches of water the system has failed the
test. Note that a fully sealed system will show a
slight increase in pressure.

6. Should the system fail the test, maintain the

pressure in the system and apply a soap
solution round all the joints and connections until
bubbles appear to reveal the source of the leak.

7. Repeat the test and if successful, dismantle the

test equipment and reconnect the pipe to the
EVAP canister.

EMISSION CONTROL

1

REPAIR

EVAP CANISTER AND PURGE CONTROL VALVE

Service repair no - 17.15.13

Remove

1. Remove 3 clips securing purge pipe to coolant

hose.

2. Depress tags and disconnect purge pipe from

plenum chamber.

3. Remove PAS reservoir clamp bracket bolt.
4. Open clamp and release reservoir from bracket.
5. Remove 2 nuts securing bracket to wing.

6. Release bracket from wing and disconnect

multiplug from purge valve.

7. Release clip and disconnect fuel tank vapour

separator pipe from canister pipe.

8. Move PAS reservoir aside, release and remove

charcoal canister, purge valve and bracket
assembly.

Do not carry out further dismantling if component
is removed for access only.

9. Remove bracket from purge valve.

Refit

10. Fit bracket to purge valve.
11. Position assembly, connect vapour separator

pipe to canister pipe and secure with clip.

12. Locate purge valve bracket and expansion hose

clip to studs and locate assembly to wing.

13. Fit and tighten nuts.
14. Locate PAS reservoir to bracket clip, compress

clip, fit bolt and tighten to

8 Nm, 6 lb ft.

15. Connect purge pipe to plenum chamber.
16. Secure purge pipe to coolant hose with clips.

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