Jaguar AJV8 engine / 5HP24 transmission. Manual - part 14

AJ-V8/5HP24

57

Engine Management

CRUISE CONTROL VACUUM SYSTEM

Reservoirs

Check Valve

VSV 1

303-121

Stability/Traction Control

If the CAN- TORQUE REDUCTION THROTTLE
message from the brake control module requests
torque reduction, the ECM reduces the throttle
valve opening. It also changes the CAN-
TRACTION ACKNOWLEDGE message to confirm
that torque reduction is in progress.

Engine Power Limiting

If the TCM detects a fault in the transmission, it
changes the CAN- TRANSMISSION OVERLOAD
message to request an engine torque limit. The
ECM then limits throttle valve opening to 18˚
maximum in all forward gears.

Vehicle Speed Limiting

The ECM uses throttle control to limit the
vehicle's maximum speed to 248 km/h (155
mph).

Reverse Gear Torque Reduction

When reverse gear is selected the CAN-
TRANSMISSION OVERLOAD message from the
TCM requests an engine torque limit. The ECM
then limits throttle valve opening to 18˚
maximum.

VSV 2

VSV 3

AJ-V8/5HP24

58

Engine Management

Fuel Injection

The ECM operates eight injectors to provide the
engine with fuel. The amount of fuel required is
determined from a base air:fuel ratio which is
then adjusted for specific operating conditions.
The ECM varies the number and duration of
injector pulses per engine cycle to regulate the
fuel flow. Injector timing is synchronised with
engine rotation, except during starting and
acceleration.
Feedback signals from the two HO2S in the
vehicle's exhaust system enable the ECM to
exercise closed loop fueling control and adaptive
fueling. Separate channels in the ECM control
each bank of injectors.
Adaptive fueling accommodates engine efficiency
variations, system tolerances and engine ageing.
Adaptations are produced at idle speed and four
other points through the RPM/load range, on a
fully warm engine, when the adaptive fueling
function centralizes the feedback range. The ECM
retains the adaptations in memory, for use in
subsequent driving cycles. If the difference
between the new and previous adaptations is
excessive, a DTC is logged in the ECM memory.
If the battery supply to the ECM is disrupted (eg.
battery disconnection), the adaptations are lost
from memory. On restoration of the battery
supply, engine operation may be uneven until the
adaptations are restored, especially at idle speed.

An output from the ECM controls the relay that
operates the fuel pump. At ignition on, the pump
will operate for 2 seconds without the ignition
switch being set to crank, after which time the
pump will be de-energized. Similarly, if the engine
stops with the ignition on, the pump will be de-
energized after 2 seconds. The pump operates
continuously while the ignition switch is set to
crank, or to on with the engine running.

FUEL PUMP CONTROL

B+ Battery

B+ Ignition

Fuel Pump
Relay

Trunk
Fuse Box

ECM

Fuel Pump

F7

303-134

Fuel Pump

The two O2S in the vehicle's exhaust system
provide inputs which enable the ECM to monitor
the efficiency of the downpipe catalytic
converters. These inputs also enable the ECM to
modify the HO2S inputs, to optimise the life of
the catalytic converters.

Base Fuel Map

The ECM contains a base fuel map that corrects
the base air:fuel ratio to the optimum mixture for
a nominal engine throughout the engine speed
and load ranges.

Battery Voltage Correction

Fuel flow through the injectors changes with
voltage, so the ECM monitors their supply
voltage and compensates for any variation from
the nominal.

AJ-V8/5HP24

59

Engine Management

Starting

The fueling start strategy operates independent
of accelerator pedal position or movement, with
the exception of a wide open throttle. The ECM
produces steady state running at the target idle
speed within 2 seconds of firing, after an
overshoot of 200 to 300 RPM maximum.
If the accelerator pedal demands a wide open
throttle during cranking, the ECM disables fuel
injection (and signals the throttle valve to the fully
open position) to clear the fuel vapor from a
"flooded" engine.

Warm-up Enrichment

During engine warm-up, the ECM determines the
fuel required from maps which modify an
enrichment factor for coolant temperature,
engine speed and load.

Transient Fueling

During acceleration and deceleration, the ECM
adjusts fueling to optimise the air:fuel ratio for
exhaust emission, response and economy. This
function operates over the full temperature range
for all acceleration and deceleration rates.

Full Load Enrichment

At full load, the ECM inhibits closed loop fueling
and increases the fuel supply to enrich the air:fuel
ratio. Full load is derived from throttle valve
position and engine speed. The degree of
enrichment is dependent on engine speed.

Engine Overspeed Protection

The ECM disables fuel injection if engine speed
reaches 7100 RPM. Fuel injection is re-instated
when RPM falls to 7050.

Stability/Traction Control

If the CAN-FAST TORQUE REDUCTION
CYLINDER message from the BCM requests fuel
intervention, the ECM reduces engine torque by
disabling fuel injection until the throttle valve
reaches its required torque reduction position. It
also changes the CAN-TRACTION
ACKNOWLEDGE message to confirm that torque
reduction is in progress.

Ignition

The ECM supplies two ignition amplifier
modules, which each supply four spark plug
mounted ignition coils. The ECM varies the
ignition timing to optimise power, emissions and
driveability at all operating conditions.
A diagnostic signal from each amplifier module
enables the ECM to monitor the supply to each
ignition coil. If the ECM detects a failure it
disables fuel injection to the affected cylinder.

IGNITION AMPLIFIER MODULES

303-091

Over-run Fuel Cut-off

When the throttle is closed at high engine
speeds, the ECM disables fuel injection until the
engine is at a lower speed. The speeds at which
fuel injection is disabled and re-instated are
mapped against coolant temperature.
On re-instatement the ECM uses a lean air:fuel
ratio, to provide a smooth transition between the
two states, which it then progressively returns to
the nominal. The initial injector pulses are given a
correction value to compensate for cylinder wall
wetting. The ECM derives the air:fuel ratio for re-
instatement from throttle valve position and
engine speed.
During over-run fuel cut-off, operation of the
EVAP valve, EGR valve (where fitted) and closed
loop fueling are inhibited.

AJ-V8/5HP24

60

Engine Management

Base Ignition Map

A base ignition map contains optimum timing for
a nominal engine throughout the engine speed
and load ranges. Corrections are then added to
adjust for specific operating conditions.

Temperature Corrections

Corrections are added to the ignition timing to
compensate for variations in intake air
temperature and engine coolant temperature.

Knock Control

Between 700 and 6800 RPM, the ECM retards
the ignition timing of individual cylinders if it
detects detonation. Also, during acceleration at
critical load and speed conditions, the ECM
retards the ignition timing to prevent the onset of
detonation.

Full Load Advance

At full load, the ECM advances the ignition timing
at the same time as fuel enrichment is applied.
The degree of advancement is dependent on
engine speed.

Fuel Cut-off Interaction

Immediately prior to over-run fuel cut-off, the
ECM retards the ignition timing to provide a
smooth transition between the two states. On
fueling re-instatement the ECM progressively
returns the ignition timing to the nominal.
Throttle valve position and engine speed
determine the rate at which the timing is returned
to the nominal.

Starting

The ECM incorporates separate timing values for
starting.

EGR

The ignition timing is advanced while the EGR
system is active. The degree of advancement is
dependent on engine speed and load.

Gear Shift Management

When the TCM decides a gear shift is necessary,
it requests a percentage torque reduction using
the CAN - TORQUE REDUCTION REQUEST
message. The ECM then retards the ignition
timing sufficient to achieve the torque reduction
requested. As the ECM retards the ignition, it

changes the CAN-TORQUE REDUCTION
ACKNOWLEDGE message to the TCM to trigger
the gear shift. 

Transient Interaction

A correction is applied to the ignition timing
during throttle transients. The correction is
against rate of change for both opening and
closing of the throttle.

Stability/Traction Control

If the CAN-FAST TORQUE REDUCTION
IGNITION message from the BCM requests
ignition intervention, the ECM retards the ignition
by the amount requested until the throttle valve
reaches its required torque reduction position. It
also changes the CAN-TRACTION
ACKNOWLEDGE message to confirm that torque
reduction is in progress.

EVAP System

The ECM operates the EVAP valve to purge the
fuel vapor from the carbon canister. Purge rates
(ie. the amount the EVAP valve opens) are a
function of engine operating conditions and the
vapor concentration level.
The engine operating conditions that affect the
purge rate are:
•

speed and load

•

coolant temperature

•

time from start-up

•

closed loop fueling.

To determine the vapor concentration level, the
ECM applies stepped opening signals to the
EVAP valve and monitors the subsequent fueling
correction. This is usually performed prior to
purging, so that when purging starts, the EVAP
valve can immediately be set to the optimum
position. If the ECM is unable to determine the
vapor concentration before purging, it uses a
default value which it then modifies while purging
is in progress. During purging, the ECM applies a
correction to the basic fueling calculation based
on the vapor concentration level.
Purging is inhibited during fuel cut-off and
stability/traction control fueling intervention.