1999 LAND ROVER DEFENDER engine

ENGINE MANAGEMENT SYSTEM
15
DESCRIPTION AND OPERATION SENSOR - THROTTLE POSITION (TP)
FROM VIN 607225
Defender vehicles from VIN 607225 use three track thick film potentiometers. No idle speed sender switch is used
on this type of sensor because the ECM can compare the two or three sets of signals to implement idle speed
control and over-run fuel shut-off. The two potentiometers are known as track 1 and 2 potentiometers. The track 3
potentiometer on later models is used to improve the resolution of the pedal. The ECM provides a 5V supply and
receives a signal from each of the potentiometer tracks.
Td5 TP Sensor Signal Output
A = Track 1
B = Track 2
C = Track 3
D = Voltage
E = Pedal Angle (Degrees)
F = Not applicable for Defender
G = Wide open throttle stop tolerance band
With reference to the above graph, at idle (throttle released), track 2 returns a signal of 4.2V to the ECM and track
1 returns a signal of 0.8V. The ECM calculates the sum of these two figures which totals 5.0V.
ProCarManuals.com

18ENGINE MANAGEMENT SYSTEM
16
DESCRIPTION AND OPERATION On Defender models, at wide open throttle, track 2 returns a signal of 0.28V and track 1 returns a signal of 4.7V to
the ECM. The ECM calculates the sum of these two figures which totals 5.0V.
The ECM uses this strategy to error check the TP sensor signal and ensure that the requested throttle position is
applied. The third potentiometer track measures the tolerance of tracks 1 and 2 and provides an improved
functionality check of the pedal angle.
NOTE: Three track TP sensors cannot be fitted as replacements on vehicles previously fitted with
two track TP sensors. Replacement ECM’s are configured for two track TP sensors and can be
fitted to all Td5 models. When replacement ECM’s are fitted to vehicles using three track TP
sensors, TestBook must be used to configure the ECM for three track TP sensor use.
If the TP sensor fails, the ECM will illuminate the MIL and the engine will operate at normal idle speed only.
ProCarManuals.com

ENGINE MANAGEMENT SYSTEM
17
DESCRIPTION AND OPERATION This page is intentionally left blank
ProCarManuals.com

18ENGINE MANAGEMENT SYSTEM
18
DESCRIPTION AND OPERATION ELECTRONIC UNIT INJECTOR (EUI)
The EUI’s are located in the top of the engine inside the camshaft cover. There is one EUI per cylinder. They inject
finely atomised fuel directly into the combustion chamber. Each EUI has its own electrical connection, which is
linked to a common harness also located under the camshaft cover. Each of the EUI’s has its own 5 letter grading
code. This code is used so that greater EUI precision is achieved.
Using an injection timing map within its memory and information from the CKP sensor the ECM is able to
determine precise crankshaft angle. When the ECM determines the crankshaft speed and position it closes the
spill valve within the EUI. Fuel pressure rises inside the EUI to a predetermined limit of 1500 bar (22,000 lbf.in
2)on
pre EU3 models, and 1750 bar (25,500 lbf.in2) on EU3 models . At this limit the pintle lifts off its seat allowing the
fuel to inject into the combustion chamber. The ECM de-energises the spill valve to control the quantity of fuel
delivered. This causes a rapid pressure drop within the EUI which allows the EUI return spring to re-seat the
pintle, ending fuel delivery.
The electrical circuit that drives the EUI works in two stages depending on battery voltage. If battery voltage is
between 9 and 16 volts the EUI’s will provide normal engine performance. If however battery voltage falls to
between 6 and 9 volts on pre EU3 models, EUI operation is restricted to a limit of 2100 rev/min. On EU3 models,
EUI operation is restricted to idle. If the vehicle is fitted with a new ECM, the EUI grades for that specific vehicle
must be downloaded to the new ECM using TestBook. In the event of the engine failing to rev above 3000 rev/min
it is probable that the EUI grading has not been completed.
Input / Output
Input to the EUI takes the form of both mechanical and electrical signals. The mechanical input to the EUI is diesel
fuel via the fuel pump operating at approximately 4 to 5 bar (58 to 72 lbf.in
2). Each of the EUI’s is operated
mechanically by an overhead camshaft to enable injection pressures of up to 1500 bar (22,000 lbf.in2) on pre EU3
models, and 1750 bar (25,500 lbf.in2) on EU3 models, to be achieved. The ECM controls the EUI’s to ensure that
fuel delivery is precise and as intended.
The EUI’s earth paths are as follows:
EUI 1 (C0522-1) via the ECM (C0158-25) on a yellow wire.
EUI 2 (C0523-1) via the ECM (C0158-26) on a yellow/brown wire.
EUI 3 (C0524-1) via the ECM (C0158-27) on a yellow/blue wire.
EUI 4 (C0525-1) via the ECM (C0158-24) on a yellow/red wire.
EUI 5 (C0526-1) via the ECM (C0158-1) on a yellow/purple wire.
ProCarManuals.com

ENGINE MANAGEMENT SYSTEM
19
DESCRIPTION AND OPERATION The EUI can fail if one or more of the following occurs:
Open circuit.
Short circuit to voltage supply.
Short circuit to vehicle earth.
Wiring loom fault.
Connector water ingress.
Connector failure due to excess heat.
In the event of an EUI failure, any of the following symptoms may be observed:
Engine misfire.
Idle faults.
Reduced engine performance.
Reduced fuel economy.
Difficult cold start.
Difficult hot start.
Excess smoke.
ProCarManuals.com

18ENGINE MANAGEMENT SYSTEM
20
DESCRIPTION AND OPERATION SENSOR - FUEL TEMPERATURE (FT)
The FT sensor is located at the RH rear of the engine in the connector block, with the tip of the sensor inserted at
least 10mm into the fuel flow. This allows the sensor to respond correctly to changes in fuel density in relation to
fuel temperature.
The FT sensor works as an NTC sensor. As fuel temperature rises the resistance in the sensor decreases. As
temperature decreases the resistance in the sensor increases. The ECM is able to compare the voltage signal to
stored values and compensates fuel delivery as necessary for hot engine start.
The operating range of the sensor is -40 to 130°C (-40 to 266°F).
Input / Output
The ECM (C0158-19) provides the FT sensor (C0184-2) with a 5 volt supply signal on a yellow/white wire. The
sensor is earthed (C0184-1) via the ECM (C0158-5) on a pink/black wire.
The FT sensor can fail or supply an incorrect signal if one or more of the following occurs:
Sensor open circuit.
Short circuit to vehicle supply.
Short circuit to vehicle earth.
Sensor fitted incorrectly.
In the event of an FT sensor signal failure any of the following symptoms may be observed:
Difficult cold start.
Difficult hot start.
Driveability concern.
In the event of a component failure, the ECM reverts to a fixed value of 60°C stored in its memory.
ProCarManuals.com

ENGINE MANAGEMENT SYSTEM
21
DESCRIPTION AND OPERATION RELAY - FUEL PUMP
The fuel pump relay is located in the engine compartment fuse box. It switches on the fuel pump to draw fuel from
the tank to the electronic unit injectors (EUI).
Input / Output
The fuel pump relay is a 4 pin normally open relay. The fuel pump relay (C0730-4) is provided with a feed by the
main relay (C0063-78) via header 291 on a brown/orange wire. An earth path is provided for the fuel pump relay
(C0730-6) via the ECM (C658-5) on a blue/purple wire. This energises the fuel pump relay and allows a feed to be
provided to the fuel pump. When the ECM interrupts the earth, the relay is de-energised and the fuel pump stops
operating.
The fuel pump relay can fail in one or more of the following ways:
Relay open circuit.
Short circuit to vehicle supply.
Short circuit to vehicle earth.
Broken relay return spring.
In the event of a fuel pump relay failure any of the following symptoms may be observed:
Engine will crank but not start.
If the engine is running, it will stop.
RELAY - MAIN
The main relay is located in the engine compartment fuse box and supplies battery voltage to the following:
The ECM.
The MAF sensor.
Fuel pump relay.
Input / Output
The main relay is a 4 pin normally open relay, which must be energised to provide a voltage to the ECM. The main
relay (C0063-86) is provided with an earth path via a transistor within the ECM (C0658-21) on a blue/red wire.
When the earth path is completed, the relay is energised and supplies the ECM (C0658-3, C0658-22 & C0658-27)
with a feed on brown/orange wires via header 291.
The main relay can fail in the following ways:
Relay open circuit.
Short circuit to vehicle supply.
Short circuit to vehicle earth.
Broken relay return spring.
In the event of a main relay failure any of the following symptoms may be observed:
Engine will crank but not start.
If the engine is running, it will stop.
For the ECM start up to take place the ignition feed when the switch is in position’II’must be greater than 6.0
volts.
ProCarManuals.com

18ENGINE MANAGEMENT SYSTEM
22
DESCRIPTION AND OPERATION SWITCH - BRAKE PEDAL
The brake pedal switch is located at the rear of the brake pedal box, and activates when the brake pedal is
operated. The ECM uses the signal from the brake pedal to activate the brake lamps and to limit fuelling under
braking.
The brake pedal switch can fail in any of the following ways:
Switch open circuit.
Short circuit to vehicle supply.
Short circuit to earth.
SWITCH - CLUTCH PEDAL
The clutch pedal switch is located on the clutch master cylinder and is activated when the clutch pedal is operated.
The ECM uses the signal from the clutch pedal switch to provide surge damping during gear change. Surge
damping stops engine speed rising dramatically (engine flaring) during gear change. Surge damping assists
driveability as follows:
Smoother gear change.
Greater exhaust gas emission control.
Improved fuel consumption.
Input / Output
When the clutch pedal is in the rest position, the clutch switch is closed. This allows a feed to flow from the switch
(C0667-1) to the ECM (C0658-35) on a black/white wire. When the clutch pedal is pressed the switch contacts
open, cutting the feed to the ECM.
The clutch pedal switch can fail in any one of the following ways:
Switch open circuit.
Short circuit to vehicle supply.
Short circuit to vehicle earth.
In the event of a clutch pedal switch failure surge damping will be inactive.
ProCarManuals.com