1995 LAND ROVER DISCOVERY ABS

Mpi
3
DESCRIPTION AND OPERATION Fuel system
ECM
The MEMS system is controlled by the ECM which is
located in the engine compartment.
The ECM is an adaptive unit and can learn the load
and wear characteristics of a particular engine.
The ECM remembers and updates two main engine
requirements when the engine is fully warm:
1.The idle stepper position required to achieve the
specified idle speed.
2.The fuelling change or offset required to achieve
a set oxygen sensor voltage.
The stepper position is used as a reference to update
the amount of stepper motor movement required to
achieve the specified idle speed under all conditions.
The fuelling offset is required to enable the system
when not in closed loop control to provide the correct
fuelling and while in closed loop control to prevent
having to apply excessive adjustments to the fuelling
which can adversely affect the emissions and
driveability.
NOTE: After fitting a different ECM, a full
tune procedure must be carried out using
Testbook.
The ECM inputs and outputs are shown in the table.INPUTS TO MEMS ECM
Crankshaft sensor
Manifold absolute pressure
Coolant temperature sensor
Inlet air temperature sensor
Knock sensor
Oxygen sensor
Throttle potentiometer
Throttle closed
Battery supply
Ignition supply
Diagnostic input
Power earth
Sensor earth
Fuel temperature sensor
Oxygen sensor
Air conditioning switch
OUTPUTS FROM MEMS ECM
Ignition coil
Injectors
Aircon relays
Stepper motor
Temperature gauge
Fuel pump relay (inside relay module)
Main relay (inside relay module)
Diagnostic output

Mpi
9
DESCRIPTION AND OPERATION SYSTEM OPERATION
Ignition on
When the ignition is switched on, voltage is applied to
ECM pin 11. The ECM then switches on the main
relay by supplying an earth path at pin 4. This allows
battery voltage to pass to ECM pin 28, to the four
injectors and through the ignition coil to ECM pin 25.
In addition, the fuel pump relay is switched on by the
ECM supplying an earth path on pin 20. Voltage is
applied through the inertia switch to the fuel pump.
The pump runs for a short period to pressurise the
fuel rail. The fuel pressure regulator will open at its
maximum setting and excess fuel is spill returned to
the tank.
The ECM determines the amount of stepper motor
movement from the following signals:
·Engine coolant temperature data at pin 33.
·Inlet air temperature data at pin 16.
·Throttle potentiometer data at pin 8.
·Engine speed data at pins 31 and 32.
·Manifold absolute pressure data (via pipe from
manifold).
·Battery voltage at pin 28.
·Ignition signal at pin 11.
If one or more of the following inputs fail, the ECM will
substitute the back-up values shown to maintain
driveability.
Input Back-up value
Coolant temperature Idle Speed controlled until
engine is fully warm. 60°Cat
speeds above idle.
Inlet air temperature Derived from engine speed and
engine load.
Manifold absolute Derived from engine speed and
pressure throttle position.
Starter operation
Whilst the starter relay is energised, battery voltage is
applied to the starter motor solenoid. The solenoid
also energises and supplies battery voltage directly to
the starter motor.
Ignition is controlled by the ECM switching the low
tension circuit via pin 25.
The ECM provides an earth signal on pins 24, 23, 26
and 1 for the period the injectors are required to be
open, the injector solenoids are energised
(simultaneously on naturally aspirated models) and
fuel is sprayed into the manifold onto the back of the
inlet valves. The ECM carefully meters the amount of
fuel injected by adjusting the injector opening period
(pulse width). During cranking, when the engine
speed is below approx. 400 rev/min, the ECM
increases the injector pulse width to aid starting. The
amount of increase depends upon coolant
temperature. To prevent flooding, injector pulses are
intermittent i.e. 24 on then 8 pulses off.
Idling
After start enrichment is provided at all temperatures
immediately cranking ceases. The ECM controls the
enrichment by increasing injector pulse width. The
enrichment decays in relation to the rising coolant
temperature.
Provided the ECM is receiving a signal that the engine
speed is close to the idle speed set point, the ECM
will implement idle speed control.
The ECM activates a unipolar stepper motor acting
directly on the throttle lever. Idle speed response is
improved by the ignition system advancing or
retarding the timing when load is placed on, or
removed from the engine.
If, during engine idle, the load on the engine is
increased sufficiently to cause engine speed to fall,
the ECM will sense this via the crankshaft sensor and
instantly advance the ignition timing to increase idle
speed and then energise the stepper motor to open
the throttle disc thus maintaining the idle speed.
Finally the ignition timing is retarded to its nominal
value.
The ECM monitors battery voltage and, if voltage falls
sufficiently to cause fluctuations in injector pulse
widths, it increases the injector pulse widths to
compensate.
On return to idle, the ECM will implement a slightly
higher idle speed to prevent the engine stalling.

19FUEL SYSTEM
10
DESCRIPTION AND OPERATION
Driving
When the throttle pedal is depressed, the ECM
implements the cruise air/fuel ratio map. During
driving the ECM continually monitors inlet air
temperature and engine speed and load for it's air
flow calculations, together with coolant temperature
for any temperature corrections. Additional inputs are
throttle potentiometer for acceleration and throttle
pedal switch for cruise/idle fuel map selection and
over-run fuel cut-off.
Acceleration enrichment
When the throttle pedal is depressed, the ECM
receives a rising voltage from the throttle
potentiometer and detects a rise in manifold pressure
from the manifold absolute pressure sensor. The ECM
provides additional fuel by increasing the normal
injector pulse width and also provides a small number
of extra injector pulses on rapid throttle openings.
Over-run fuel cut-off
The ECM implements over-run fuel cut-off when the
following signals are received.
·Throttle disc closed.
·Engine speed is above 2000 rev/min - engine at
normal operating temperature.
Fuel is reinstated progressively when any of the
above signals cease.
Over-speed fuel cut-off
To prevent damage at high engine speeds the ECM
inhibits the earth path for the injectors, cutting off
injection. As engine speed falls, injection is reinstated.
Ignition switch off
When the ignition is switched off, the ECM will keep
the main relay energised for approx. 30 seconds while
it drives the stepper motor to the 35 step position for
the next engine start.

Mpi
9
REPAIR
Refit
9.Examine flexible mounting for splits or damage;
renew as necessary.
10.Thoroughly clean throttle housing and mating
face of flexible mounting.
11.Connect breather hose to throttle housing.
12.Position throttle housing to mounting studs, fit
nuts. Tighten to
7 Nm.
13.Connect throttle cable to cam.
14.Adjust throttle cable.
15.Connect multiplug to stepper motor.
16.Connect multiplug to throttle potentiometer.
17.Connect hose to throttle housing, tighten clip.FUEL PRESSURE REGULATOR
Service repair no - 19.45.06
Remove
1.Disconnect battery negative lead.
2.Position absorbant cloth around fuel pipe to fuel
rail union. Loosen bolt to relieve pressure.
Re-tighten bolt.
3.Release clip and disconnect fuel hose from
pressure regulator.
CAUTION: Plug the connectors.
4.Disconnect intake air temperature sensor
multiplug.
5.Remove 4 bolts securing pressure regulator
steady bracket to fuel rail and manifold, remove
steady bracket.
6.Disconnect vacuum hose from pressure
regulator.
7.Manoeuvre pressure regulator from fuel rail.
8.Discard 'O' ring.

30MANIFOLD AND EXHAUST SYSTEM
2
REPAIR Remove
Catalysts - remove and refit 1 to 5
1.Raise vehicle on a ramp [hoist].
2. Catalyst vehicles only:Disconnect two heated
oxygen sensor wiring connectors.
NOTE: NAS models have four heated
oxygen sensors fitted.
3.Remove two nuts securing rear exhaust
assembly to front exhaust assembly.
4.Remove nuts and release front downpipes from
manifolds. Discard gaskets.
5.Lower front exhaust assembly with catalysts (if
fitted), retain olive.
NOTE: Assistance is required for removing
and refitting rear exhaust assembly.
6.Remove bolts securing three hanger brackets to
chassis. Lower exhaust assembly onto rear axle.
Detach rubbers from hanging brackets.
7.Place extended axle stands underneath chassis,
in front of chassis mounted rear towing brackets.
8.Lower ramp[hoist] until vehicle weight is
supported securely on stands.
9.Lower ramp [hoist] until rear shock absorbers
are ALMOST fully extended.
10.Move rear exhaust to a diagonal position, centre
silencer to right of vehicle.
11.Facing rear of vehicle, twist assembly
anti-clockwise clear of rear axle.
12.Remove rear exhaust assembly from vehicle.
Refit
13.Position rear exhaust assembly over rear axle in
a diagonal position, as for removing.
14.Twist assembly clockwise until it is in mounting
position.
15.Reverse removal procedure. 1. to 9. using new
manifold gaskets and applying exhaust sealer to
system joint.
16.Examine system for leaks, ensuring that system
does not foul underbody components. Rectify if
necessary.EXHAUST MANIFOLD - V8i
Service repair no - Left hand - 30.15.10
Service repair no - Right hand - 30.15.11
Remove
1.Disconnect front exhaust pipe(s) from
manifold(s).
2.Tap back bolt locking tabs and remove eight
bolts, lock tabs and washers.
3.Remove manifold(s) and old gaskets.
Refit
4.Ensure that mating surfaces of cylinder head
and exhaust manifold are clean and smooth.
5.Coat threads of each bolt with anti-seize
compound.
6.Place manifold and new gaskets in position on
cylinder head and fit securing bolts, new
lockplates and plain washers. Plain washers are
fitted between manifold and lockplates.
7.Evenly tighten manifold bolts to
20Nmbend
over lockplate tabs.
8.Reconnect front exhaust pipe, using new
exhaust flange gaskets.

MANIFOLD AND EXHAUST SYSTEM
5
REPAIR INLET MANIFOLD GASKET - Mpi
Service repair no - 30.15.08
Remove
1.Disconnect battery negative lead.
2.Position absorbent cloth around fuel pipe to fuel
rail union. Unscrew union to relieve fuel
pressure. Re-tighten union.
CAUTION: Plug connections.
3.Release clip and remove air cleaner to throttle
housing hose.
4.Disconnect stepper motor multiplug.
5.Disconnect throttle potentiometer multiplug.
6.Release throttle cable from abutment bracket.
7.Release throttle cable from cam. Remove
coolant bypass hose.
8.Disconnect fuel temperature sensor multiplug.
9.Release clip and disconnect brake servo hose
from manifold.

MANIFOLD AND EXHAUST SYSTEM
9
REPAIR MANIFOLD CHAMBER GASKET - Mpi
Service repair no - 30.15.37
Remove
1.Disconnect battery negative lead.
2.Position absorbent cloth around fuel pipe to fuel
rail union. Loosen union to relieve pressure.
Re-tighten union.
3.Release clip and remove air cleaner to throttle
housing hose.
4.Disconnect stepper motor and throttle
potentiometer multiplugs.
5.Release clip and disconnect breather hose from
throttle housing.
6.Release throttle cable from abutment bracket.
7.Release throttle cable from cam. Remove
coolant bypass hose from throttle housing.
8.Disconnect fuel temperature sensor multiplug.
9.Release clip and disconnect brake servo hose
from manifold.

33CLUTCH
2
DESCRIPTION AND OPERATION When the clutch pedal is depressed, hydraulic fluid
transmits the movement via the slave cylinder, release
lever 10, bearing 9, to the inner fingers of the
diaphragm spring 4.
The diaphragm spring 4 pivots on the bearing rings 7
and fulcrum posts 6 causing the pressure plate 5 to
release the clamping force on the friction plate and
linings 2.As the the clamping force is removed from the friction
plate 2, the plate slides on the splines of the primary
shaft 15 and takes up a neutral position between the
flywheel 1 and the pressure plate 5 , thus breaking the
drive between the engine and the gearbox.
NOTE: Diesel engined vehicles have an
hydraulic damper 19 fitted into the system.
The damper contains a steel diaphragm
which absorbs slight hydraulic pulses caused by
cyclic variations of the diesel engine crankshaft at
low rpm.