ignition system LAND ROVER DISCOVERY 1995 Owner's Guide

19FUEL SYSTEM
8
REPAIR IGNITION COILS
Service repair no - 18.20.45 - Set
Service repair no - 18.20.43 - Each
Service repair no - 18.20.44 - Extra - Each
Remove
1.Disconnect battery negative lead.
2.Disconnect H.T. leads from ignition coils. Note
positions of leads.
3.Place H.T. leads aside.
4.Disconnect ignition coil multiplug.
5.Remove 4 nuts securing coil bracket.
6.Release ignition coil bracket from inlet manifold
studs.
7.Manoeuvre coil/bracket assembly from behind
plenum chamber and remove.
8.Remove terminal cover. Note lead positions.
9.Remove 2 nuts securing leads to coil terminals.
10.Remove leads from terminals.
11.Remove 3 Torx screws securing ignition coil to
bracket and remove coil.Refit
12.Fit ignition coil to bracket. Secure with screws.
13.Connect leads to terminals. Secure with nuts.
14.Fit terminal cover.
15.Position ignition coil bracket on inlet manifold
studs.
16.Secure fuel rail and ignition coil bracket with
nuts. Tighten to
8 Nm.
17.Connect multiplug.
18.Connect H.T. leads to respective coil towers.
19.Reconnect battery negative lead.

SFI
11
REPAIR FUEL PRESSURE REGULATOR
Service repair no - 19.45.06
Remove
1.Disconnect battery negative lead.
2.Depressurise fuel system.
See Fuel System -
Depressurise
3.Position cloth over fuel feed union, slacken union
to release fuel pressure, then re-tighten union.
4.Release fuel return hose clip. Remove fuel
return hose from regulator connecting pipe.
5.Plug connections.
6.Remove 4 nuts ignition coil bracket to inlet
manifold.
7.Release ignition coil bracket from inlet manifold
studs and place aside.
8.Release regulator connecting pipe from clip.
9.Disconnect vacuum hose from fuel pressure
regulator.
10.Remove 2 bolts securing fuel pressure regulator
to fuel rail.
11.Remove fuel pressure regulator assembly.
12.Remove 'O' ring and spacer ring from fuel
pressure regulator. Discard 'O' ring.
13.Release clip and remove connecting pipe from
regulator.
14.Fit plugs to regulator and rail.

19FUEL SYSTEM
12
REPAIR Refit
15.Ensure locations on fuel pressure regulator and
fuel rail are clean.
16.Fit new spacer ring and 'O' ring to fuel pressure
regulator. Lubricate 'O' ring with silicone grease.
17.Fit pressure regulator assembly to fuel rail.
18.Secure regulator connecting pipe in clip.
19.Secure with bolts. Tighten to
10 Nm.
20.Align ignition coil bracket to inlet manifold studs.
21.Secure ignition coil bracket and fuel rail to inlet
manifold with nuts. Tighten to
8 Nm.
22.Remove plugs.
23.Connect return pipe to regulator connecting pipe.
Secure with clip.
24.Connect vacuum hose to fuel pressure regulator.
25.Remove cloth.
26.Reconnect battery negative lead.
27.Start engine. Check for leaks around fuel
pressure regulator, fuel feed and fuel return
unions.IDLE AIR CONTROL (IAC)
Service repair no - 19.22.54
Remove
1.Disconnect battery negative lead.
2.Disconnect IAC multiplug.
3.Remove 2 bolts securing IAC to plenum.
4.Remove IAC.
5.Remove gasket and discard.
Refit
6.Ensure all mating faces are clean.
7.Using a new gasket, fit IAC to plenum. Secure
with bolts. Tighten to
2.3 Nm.
8.Connect multiplug.
9.Reconnect battery negative lead.

19FUEL SYSTEM
28
REPAIRADD: 09/95 Refit
26.Fit vent line to filler neck.
27.Fit NEW clip to filler neck hose.
28.Fit hose to filler neck.
29.Position filler neck hose clip and tighten until
head shears.
30.Fit filler neck assembly to vehicle.
NOTE: To aid fitment of filler neck through
body grommet apply a soap solution to lip
of grommet.
31.Fit NEW clip to fuel filler neck hose.
32.Connect fuel filler neck internal breather to tank.
33.Connect fuel filler neck hose to tank.
34.Position fuel filler neck hose clip and tighten until
head shears.
35.Connect vent line quickfit connector to
liquid/vapour separator.
36.Connect the pressure sensor breather pipe
connection.
37.Connect the vent line hose connection.
38.Fit mud flap and secure with nuts and bolts.
39.Position filler neck support bracket and earth
strap to mud flap bracket and secure with nut
and bolt.
40.Remove stand(s) and lower vehicle.
41.Reposition loadspace sound insulation and
carpet.
42.Fit RH luggage compartment side panel.
See
CHASSIS AND BODY, Repair,
43.Fit tail door tread strip and secure with screws.
44.Refill tank with drained fuel.
45.Fit fuel filler cap to filler neck.
46.Close filler flap, lock with ignition key and
remove key.
47.Reconnect battery negative lead.FUEL TANK FILLER CAP - ADVANCED EVAPS
Service repair no - 19.55.08
Remove
1.Fit ignition key to fuel filler flap lock and open
flap.
2.Remove screw securing cap retaining strap to
body.
3.Remove fuel filler cap.
Refit
4.Fit fuel filler cap.
5.Position cap retaining strap to body and secure
with screw.
6.Close filler flap, lock with ignition key and
remove key.

Mpi
1
DESCRIPTION AND OPERATION DESCRIPTION
The Mpi Modular Engine Management System
(MEMS) controls the fuel injection and programmed
ignition systems.
The main features are as follows:
·The Engine Control Module (ECM) controls
programmed ignition and fuel injection. The ECM
incorporates short circuit protection and can
store intermittent faults on certain inputs.
Testbook can interrogate the ECM for these
stored faults.
·The ECM uses the speed/density method of air
flow measurement to calculate fuel delivery. This
method measures the inlet air temperature and
inlet manifold pressure and assumes that the
engine is a calibrated vacuum pump with its
characteristics stored in the ECM
·If certain system inputs fail, the ECM implements
a back-up facility to enable the system to
continue functioning, although at a reduced level
of performance.
·A separate diagnostic connector allows engine
tuning or fault diagnosis to be carried out using
Testbook without disconnecting the ECM
harness connector.
·The ECM harness multiplug incorporates
specially plated pins to minimise oxidation and
give improved reliability.
·The throttle potentiometer requires no
adjustment in service. The following components
supply data for both fuelling and ignition:Ignition system
The ECM determines the optimum ignition timing
based on the signals it receives from the following
sensors:
1.Crankshaft sensor - Engine speed and
crankshaft position.
2.Manifold absolute pressure sensor - Engine load
3.Coolant temperature sensor - Engine
temperature.
4.Manifold absolute pressure sensor - Throttle
closed.
5.Knock sensor - Engine noise and vibration.
MEMS uses no centrifugal or vacuum advance, timing
being controlled by the ECM which is energised by the
main relay, within the relay module. Spark distribution
is achieved by 2 coils mounted at the rear of the
engine and controlled by the ECM.

19FUEL SYSTEM
2
DESCRIPTION AND OPERATION Basic ignition timing
MEMS provides the optimum ignition timing for the
relevant engine speed and load. The speed and
position of the engine is detected by the crankshaft
sensor which is bolted to, and projects through the
engine adapter plate.
The sensor incorporates an armature which runs
adjacent to a reluctor insert in the flywheel, the insert
consisting of 34 poles spaced at 10°intervals, with
two missing poles 180°apart to identify the T.D.C.
positions.
The sensor 'reads' these poles to provide a constant
up-date of engine speed and crankshaft position to
the ECM
The load signal is provided by the manifold absolute
pressure sensor mounted inside the ECM casing
which detects manifold pressure via a hose connected
to the manifold chamber. The sensor converts
pressure variations into graduated electrical signals
which can be read by the ECMIgnition timing compensation
Coolant temperature sensor
When the ECM receives a low engine temperature
signal from the coolant sensor, it provides optimum
driveability and emissions by advancing or retarding
the ignition timing.
Knock sensor
The knock sensor is a capacitive device mounted in
the cylinder block between nos. 2 and 3 cylinders
below the inlet manifold. The sensor monitors noise
and vibration in the engine and passes this
information to the ECM which is able to identify the
characteristics of the knocking and make the
necessary corrections to the ignition timing of
individual cylinders.
Idle speed control
When the throttle pedal is released and the engine is
at idle, the ECM uses the fast response of ignition
timing to assist idle speed control.
When loads are placed on, or removed from the
engine the ECM senses the change in engine speed
and in conjuction with the opening of the throttle disc
by the stepper motor, advances or retards the ignition
timing to maintain the specified idle speed. When load
is removed from the engine and the stepper motor
returns to it's original position, the ignition timing
returns to the idle setting.
NOTE: Due to the sensitivity of this system
the ignition timing will be constantly
changing at idle speed.

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
5
DESCRIPTION AND OPERATION
Fuel pump
The electric fuel pump, located inside the fuel tank, is
a self-priming centrifugal 'wet' pump, the motor and
pump are filled with fuel.
The fuel pump supplies more fuel than the maximum
load requirement for the engine, so that pressure in
the fuel system can be maintained under all
conditions.
Fuel pressure regulator
The pressure regulator is a mechanical device
controlled by manifold depression and is mounted in
the fuel rail. The regulator ensures that fuel rail
pressure is maintained at a constant pressure
difference to that in the inlet manifold, as manifold
depression increases the regulated fuel pressure is
reduced in direct proportion.
When pressure exceeds the regulator setting excess
fuel is spill returned to the fuel tank swirl pot which
contains the fuel pick-up strainer.
Relay module
The relay module contains the main relay, fuel pump
relay, starter relay and oxygen sensor relay and is
mounted on the ECM mounting bracket.
The main relay is energised when the ignition is
switched on and supplies current to the ECM
The fuel pump relay is energised by the ECM for a
short period when the ignition is switched on, during
cranking and while the engine is running.
The starter relay is energised by the cranking signal
from the ignition switch.
This oxygen sensor relay is energised when the
ignition is switched on and supplies current to the
ECM
Intake air temperature sensor
The intake air temperature sensor is fitted in the side
of the inlet manifold and sends the ECM a signal
relating to air temperature. The ECM uses this signal
in its calculations on air flow.
Inertia switch
The fuel pump circuit incorporates an inertia switch
which in the event of sudden deceleration isolates the
power supply to the fuel pump. The inertia switch is
situated in the engine compartment on the bulkhead
and can, if tripped, be reset by depressing the central
plunger.
WARNING: Check the integrity of the fuel
system before the inertia switch is reset.
Diagnostic connector
A diagnostic connector is provided to enable
diagnosis to be carried out without disturbing the
system electrical connections and to allow the ECM's
ability to store certain faults to be utilised.
Oxygen sensor - Closed-loop emission control
The MEMS Mpi system operates a closed loop
emission system to ensure the most efficient level of
exhaust gas conversion.
An oxygen sensor fitted in the exhaust manifold
monitors the exhaust gases. It then supplies a small
voltage proportional to exhaust oxygen content to the
ECM As the air/fuel mixture weakens, the exhaust
oxygen content increases and so the voltage to the
ECM decreases. If the mixture becomes richer so the
oxygen content decreases and the voltage increases.
The ECM uses this signal voltage to determine the
air/fuel mixture being delivered to the engine, and
adjusts the injector duration to maintain the ratio
necessary for efficient gas conversion by the catalyst.
The oxygen sensor has an integral heating element to
ensure an efficient operating temperature is quickly
reached from cold. The electrical supply for the heater
element is controlled by the oxygen sensor relay.
Fuel temperature sensor
The fuel temperature sensor is inserted in the fuel rail
and measures fuel and fuel rail temperatures. During
engine cranking at high temperatures, the ECM
increases fuel supply, and opens the throttle disc via
the stepper motor to aid hot starting.

19FUEL SYSTEM
8
DESCRIPTION AND OPERATION MEMS COMPONENTS & LOCATION ON ENGINE
Components Location
1 Fuel pressure regulator Engine rear...........................................
2 Intake air temperature sensor Inlet manifold.................................
3 Crankshaft sensor Under starter motor on flywheel housing...................................................
4 Twin ignition coils Engine rear....................................................
5 Oxygen sensor Exhaust manifold........................................................
6 Coolant temperature sensor Coolant chamber....................................
7 Injectors
8 Stepper motor
9 Throttle potentiometer
10 Fuel temperature sensor Fuel rail.........................................
11 Knock sensor Engine block..........................................................

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.