1995 LAND ROVER DISCOVERY fuel pressure

17EMISSION CONTROL
8
DESCRIPTION AND OPERATION ADD: 09/95 System operation
The system is designed to prevent fuel vapour
escaping to atmosphere, and consists of four roll-over
valves fitted internally in the fuel tank, connected to
the liquid/vapour separator by a nylon line. The
separator is mounted to the side of the filler neck. An
EVAP canister is positioned in the engine
compartment mounted on the right front side valance.
The liquid/vapour separator and EVAP canister are
connected by a nylon line which runs the length of the
chassis.
Pressure/vacuum relief valves are incorporated into
the fuel filler cap and are designed to protect the fuel
tank from permanent deformation in the event of
system pressure or vacuum exceeding the system
operating parameters. There are no other relief or
one-way valves in the system.
A vent line flow restrictor known as an anti-trickle fill
valve is fitted to the filler pipe in the line between the
tank and EVAP canister. The function of this valve is
to prevent overfilling the tank by trickling fuel in,
thereby preserving the vapour space in the tank to
allow for fuel expansion during hot weather.
The valve achieves this by blocking the vent line
during the fuel filling process. The valve is operated
by the action of inserting the filler gun so that when
the fuel in the tank reaches the level of the filling
breather, flow cut off occurs due to fuel filling the filler
pipe.During normal vehicle operation and when the engine
is switched off, the venting system between the fuel
tank and EVAP canister is open to allow the free
passage of vapour.
The EVAP canister, which is connected by a nylon
hose to the plenum chamber, absorbs and stores the
fuel vapour from the fuel tank when the engine is not
running. With the engine running, vapour is purged
from the EVAP canister by allowing outside air to be
drawn through the EVAP canister vent solenoid and
link pipe by the influence of manifold vacuum to the
EVAP canister purge connection on the canister.
Filter pads are fitted above and below the charcoal
and in the EVAP canister vent solenoid to prevent the
ingress of foreign matter into the purge line.
The EVAP canister purge valve, which is fitted in the
line from the EVAP canister to the plenum, is
controlled by the ECM which determines the most
emission acceptable time at which purging should
take place. This will normally be at engine speeds
above idle and when the vehicle is in motion.
The EVAP canister vent solenoid is mounted on the
side of the EVAP canister bracket and is connected to
the EVAP canister by a length of large bore hose. The
ECVS is controlled by the ECM and is normally open.
The function of the ECVS is to block the air intake
side of the EVAP canister. When the system receives
an ECM signal the valve closes; this allows the
system leak check to take place. The leak check only
occurs when pre-determined vehicle operating
conditions are met.

EMISSION CONTROL
1
FAULT DIAGNOSIS REV: 09/95 TESTING EVAPORATIVE EMISSION CONTROL -
PRE ADVANCED EVAPS
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.
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).
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 adsorption 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
adsorption canister.LEAK DETECTION PROCEDURE - ADVANCED
EVAPS
1.Connect TestBook to the vehicle and confirm
that the fault code(s) displayed relate to an
EVAP system fault.
2.Examine components in fuel and EVAP system
for damage or poorly connected joints.
3.Repair or replace components to rectify any
faults found, then reset the Check Engine light
using TestBook.
4.Carry out Drive Cycle,
See Drive Cycle -
Advanced EVAPS
5.Using TestBook confirm that the Evaporative
Loss Control (ELC) Inspection and Maintenance
(IM) flag has cleared. This procedure should
confirm that the ELC test was carried out during
the drive cycle and that the fault was cured.
6.If the IM flag is still shown, use TestBook to
interrogate the engine management system to
ascertain which of the following situations exists:
·If a fault code is shown then further investigation
is required, proceed to the next step.
·If the IM flag is still shown, but no faults are
indicated the conditions for the ELC check have
not been met and the drive cycle must be
repeated.
7.Connect the Leak Detection/EVAP Diagnostic
Station to the vehicle and carry out the
procedures given in the operating instructions
supplied with the equipment.
8.Rectify faults indicated by the Leak
Detection/EVAP Diagnostic Station and return to
step 4.

19FUEL SYSTEM
4
DESCRIPTION AND OPERATION OPERATION
Diesel engines operate by compression ignition. The
rapid compression of air in the cylinder during the
compression cycle heats the injected fuel, causing it
to self ignite. During cold starting, automatically
controlled glow plugs assist in raising the temperature
of the compressed air to ignition point.
A cold start advance unit advances the injection timing
to further assist starting. Idle quality is improved by
the high idle setting.
The engine is supplied with pre-compressed air by a
single stage turbocharger.
Exhaust gases passing over a turbine cause it to
rotate, driving a compressor mounted on the turbine
shaft. Air drawn from the cold air intake passes, via
the air cleaner, to the turbocharger where it is
compressed. The compressed air passes to the
cylinders via an intercooler, which reduces the
temperature of the compressed air, increasing its
density.
Fuel is drawn from the tank by a mechanical lift pump
and passes to the injection pump via a filter. In
addition to removing particle contamination from the
fuel, the filter incorporates a water separator, which
removes and stores both bound and unbound water.
The injection pump meters a precisely timed, exact
quantity of fuel to the injectors in response to throttle
variations, injection timing varying with engine speed.
Any excess fuel delivered to the injection pump is not
injected, passing back to the tank via the fuel return
line.
Fuel is injected in a finely atomised form into a
pre-combustion chamber in the cylinder head where it
ignites. The burning fuel expands rapidly into the main
combustion chamber, creating extreme turbulence
which mixes the burning fuel thoroughly with the
compressed air, providing complete combustion.
Cold Starting is assisted by glow plugs, a cold start
advance unit and a high idle setting.Glow plugs
Glow plug operation is controlled by a timer unit, start
relay and resistor. When the ignition is turned on the
timer unit is energised, the glow plugs start to operate
and a warning light on the dashboard illuminates,
remaining illuminated until the glow plugs are
automatically switched off.
The length of time the glow plugs will operate is
dependent on under bonnet temperature, which is
monitored by a sensor located in the timer unit.
Starting the engine results in the power supply to the
glow plugs passing through the resistor, which
reduces their operating temperature. The glow plugs
are cut out either by the temperature sensor in the
timer, or by a microswitch on the injection pump which
operates when the throttle is depressed.
Cold start advance
The cold start advance unit is connected to the engine
cooling system via hoses. It contains a temperature
sensitive element which is retracted when cold and
pulls the advance lever, via cable, towards the rear of
the pump against spring pressure. As coolant
temperature rises, the cold start element expands
releasing tension on the cable and allowing spring
pressure to move the advance lever forwards.

19FUEL SYSTEM
6
DESCRIPTION AND OPERATION DESCRIPTION ELECTRONIC DIESEL CONTROL
The Electronic Diesel Control (EDC) 'drive by wire'
system derives its from the replacement of
conventional mechanical controls by electronic
components.
The EDC system supplies the exact amount of fuel to
the engine according to the prevailing engine
operating conditions. To monitor these conditions,
sensors are fitted to the engine to measure engine
parameters. Data from the sensors is received by the
Engine Control Module (ECM) which determines the
exact amount of fuel, injection timing and Exhaust
Gas Recirculation (EGR) required for any running
condition.
Safety and emergency features are built into the
system which protect the engine against overspeed
and overheating damage. In the event of component
failure the system is designed to compensate and
allow emergency start and limp home facilities to
operate. The ECM does this by substituting a default
value for the failed component which may result in a
noticeable loss in power but keeps the engine
running.FUEL SYSTEM COMPONENT LOCATION EDC
1. Vehicle speed sensor
2. No. 4 injector sensor
3. Coolant temperature sensor
4. Boost pressure sensor
5. Electro-pneumatic modulator
6. Airflow sensor
7. Engine speed sensor
8. Brake/clutch switches
9. Injector pump
10. Throttle position sensor
11. Engine control module

19FUEL SYSTEM
8
DESCRIPTION AND OPERATION FUEL SYSTEM LAYOUT EDC
1. Fuel injection pump
2. Fuel temperature sensor
3. Air temperature sensor
4. Water temperature sensor
5. No. 4 injector sensor
6. Air flow sensor
7. Engine speed sensor
8. Boost pressure sensor
9. Vehicle speed sensor
10. Clutch switch
11. Brake switch
12. Throttle position sensor
13. Electro-pneumatic modulator
14. Exhaust gas recirculation (EGR) valve
15. Engine control module (ECM)
16. Diagnostic indicator
A. To turbo
B. To air box.
C. To 'T' piece on brake servo hose position
D. Solenoid operated valve energization timing device.
E. Fuel cut off
F. Actuator current
G. Control collar

Tdi
9
DESCRIPTION AND OPERATION OPERATION EDC
Under start up conditions, signals from the crank
speed and water temperature sensors are relayed to
the ECM to control starting fuel quantity and injection
timing. Once the engine has started the ECM initiates
a 'closed loop' monitoring system for fuel quantity,
injector timing and EGR relative to the appropriate
engine operating conditions.
As driver demand increases, signals from the throttle
position sensor are received by the ECM together with
crank speed and position pulses. The ECM signals
the injection pump to adjust fuel quantity and timing
relative to driver demand.
As engine coolant, fuel and air temperature changes
the ECM will correct fuel delivery and injection timing
for more efficient and accurate running. The ECM will
also make corrections for atmospheric pressure on
injection timing and EGR.
Electronic Control Unit (ECM)
The EDC system is controlled by the ECM located in
the drivers footwell on the 'A' post beneath the fascia.
The unit consists of a microprocessor with integrated
circuits and components and is connected to the main
harness by a 55 pin plug.
Inputs to the ECM from engine sensors control start of
injection, injected fuel quantity, fuel cut-off and EGR.
The ECM will also make corrections for engine
coolant, fuel and air temperature and atmospheric
pressure.Injection pump
The injection pump incorporates actuator controlled
injected fuel quantity and solenoid operated timing
which operate in response to ECM signals against
driver demand, engine speed, temperature and boost
pressure.
A fuel cut-off facility and fuel temperature sensor is
incorporated in the pump.
Injection timing sensor
An inductive sensor in No 4 injector body monitors
needle movement. This forms part of a 'closed loop'
system to control start of injection.
The system measures timing, relating the needle
movement signal to crank position (determined by
flywheel pulses from the engine speed sensor).
Air flow sensor
The Air Flow Sensor is mounted on a bracket
attached to the wheel arch valance, and connected by
hose to the air cleaner and turbo charger inlet.
The unit consists of a flap valve airflow sensor which
measures the fresh air flow into the engine. The
sensor informs the ECM and, provided that the other
conditions are met, will implement EGR.
Engine speed sensor
The engine speed sensor is an active inductive sensor
mounted on the flywheel housing. Pulses from the
sensor activated by radial slots in the flywheel give
engine speed and position information to the ECM.

19FUEL SYSTEM
10
DESCRIPTION AND OPERATION Vehicle speed sensor
The vehicle speed sensor is located on the transfer
box behind the transmission brake. The unit has a
multirole as the vehicle electronic speedometer
sensor and as a sensor for 'surge damping', (a
function which smooths out engine response to sharp
accelerator movement and reduces vehicle 'bucking').
The sensor is an additional input for engine overheat
protection.
Brake and clutch switches
The brake and clutch switches are located on the
pedal box and serve as safety features to the system.
They return information to the ECM which limits
maximum fuel quantity under braking.
Throttle position sensor
The accelerator pedal is connected directly to a
sensor mounted in the pedal box. Driver demand is
relayed back to the ECM to increase or decrease
injected fuel quantity.
Incorporated in the sensor is a backup idle switch
which the system will default to in the event of sensor
failure.
Boost pressure sensor
The boost pressure sensor is mounted on the
bulkhead. It relays boost pressure information to the
ECM which compensates fuel quantity to reduce
smoke during acceleration.
Electro-pneumatic modulator
The electro-pneumatic modulator is located on the
inner wing just forward of the air cleaner. It regulates
vacuum signals from the source to the EGR valve.
The ECM controls the modulator to open the EGR
valve according to required airflow.Exhaust gas recirculation valve
The EGR valve is located on the engine exhaust
manifold and is controlled by vacuum from the
electro-pneumatic modulator.
Once open the EGR valve directs a quantity of
exhaust gas back into the inlet manifold to be burnt
inside the engine. This reduces NOx (Oxides of
nitrogen) emissions of the engine.
Temperature sensors
Water, Fuel and Air temperature sensors monitor
engine conditions and relay their information back to
the ECM which makes adjustments to injected fuel
quantity, injection timing, EGR and corrections to
measured boost pressure and airflow.

19FUEL SYSTEM
2
ADJUSTMENT LOW AND HIGH IDLE SPEED
Adjust
The high idle speed (cold start idle) is
automatically set by the setting of the low idle
speed and can not be adjusted individually.
1.Check and adjust throttle cable.
2.Start engine and run it until normal operating
temperature is reached.
3.Using a suitable tachometer, check the engine
idle speed.
See ENGINE TUNING DATA,
Information, 300 Tdi Engine
4.If adjustment is necessary, loosen the locknut on
the injector pump.
5.Turn the adjustment screw either clockwise to
increase the engine speed or anti-clockwise to
decrease the speed. Run the engine at an
increased speed for a few seconds then check
the idle speed again.
6.When the correct speed has been achieved,
hold the adjuster screw steady while tightening
the locknut.
NOTE: The low idle speed control is the
only permitted adjustment in service. Any
additional adjustments required must be
entrusted to authorised Bosch agents.CHECK TURBOCHARGER BOOST PRESSURE
For boost pressure.
See ENGINE TUNING DATA,
Information, 300 Tdi Engine
1.Disconnect, from turbocharger, hose to actuator.
Insert into a suitable "T" piece.
2.Connect a short length of suitable hose to
turbocharger and connect other end to "T" piece.
3.Connect a further length of hose to third leg of
the "T" piece and other end to a pressure gauge
capable of reading in excess of 61 cm Hg. The
pressure gauge hose must be capable of
reaching passenger compartment so that gauge
may be observed.
4.To check maximum boost pressure, drive
vehicle normally but in such a manner that full
throttle can be maintained whilst climbing a hill
with engine speed held steady between 2,500
and 3,000 rev/min.