1995 LAND ROVER DISCOVERY fuel pressure

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.

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
7
REPAIR FUEL RAIL AND INJECTORS
Service repair no - 19.60.04 - Rail
Service repair no - 19.60.10 - Injectors
Remove
1.Remove inlet manifold chamber gasket.
See
MANIFOLD AND EXHAUST SYSTEM, Repair,
Manifold Chamber Gasket - Mpi
2.Remove pressure regulator.
3.Remove 4 bolts securing fuel feed hose flange
stiffening bracket, remove stiffening bracket.
4.Release fuel feed hose from fuel rail.
5.Discard 'O' ring.
6.Disconnect 4 injector multiplugs.
7.Move injector harness aside.
8.Remove 2 bolts securing fuel rail to inlet
manifold.
9.Release 4 injectors from inlet manifold.
10.Remove fuel rail complete with injectors.
11.Discard outlet 'O' rings from injectors.
12.Fix protective cap to each injector.
Do not carry out further dismantling if component
is removed for access only.
13.Remove clip(s) securing injector(s) to fuel rail.
14.Remove injector(s).
15.Discard inlet 'O' ring(s) from injector(s).
16.Remove fuel temperature sensor.

19FUEL SYSTEM
8
REPAIR Refit
17.Clean fuel rail, temperature sensor and pressure
regulator mating surfaces.
18.Fit fuel temperature sensor. Tighten to
7Nm
19.Clean injectors and injector recesses in fuel rail
and inlet manifold.
20.Fit new 'O' ring(s) to inlet end of injector(s).
21.Fit injector(s) to fuel rail, fit and secure clip(s).
22.Fit new 'O' rings to outlet ends of injectors.
23.Align injectors to inlet manifold and push fuel rail
into position.
24.Fit fuel rail securing bolts. Tighten to
10 Nm
25.Connect injector multiplugs.
26.Remove plugs from fuel feed hose and fuel rail.
27.Fit new 'O' ring to fuel feed hose.
28.Connect fuel feed hose to fuel rail.
29.Fit stiffening bracket.
30.Tighten stiffening bracket and feed hose bolts.
31.Fit pressure regulator.
32.Fit inlet manifold chamber.THROTTLE HOUSING
Service repair no - 19.22.45
Remove
1.Loosen clip, disconnect hose from throttle
housing.
2.Disconnect multiplug from stepper motor.
3.Disconnect multiplug from throttle potentiometer.
4.Disconnect breather hose from throttle housing.
5.Loosen 2 nuts securing throttle cable to
abutment bracket and release cable.
6.Release throttle cable from cam.
7.Remove 4 nuts securing throttle housing to
flexible mounting.
8.Release throttle housing from studs.

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.

19FUEL SYSTEM
10
REPAIR
Refit
9.Clean pressure regulator and mating surfaces.
10.Fit new 'O' ring to pressure regulator.
11.Fit vacuum hose to pressure regulator.
12.Position pressure regulator.
13.Fit steady bracket.
14.Fit bolts and tighten.
15.Connect multiplug to air temperature sensor.
16.Remove plugs, fit fuel hose to regulator and
secure with clip.
17.Reconnect battery negative lead.OXYGEN SENSOR
Service repair no - 18.30.41 - L.H
Service repair no - 18.30.42 - R.H
Remove
1.Disconnect oxygen sensor multiplug.
2.Release multiplug from bracket.
3.Release harness lead from cable tie.
4.Remove oxygen sensor; recover sealing washer.
Refit
5.Fit sealing washer to oxygen sensor.
6.Fit oxygen sensor. Tighten to
55 Nm.
7.Secure multiplug to bracket, connect multiplug.
8.Secure harness lead with cable tie.