Jaguar AJV8 engine / 5HP24 transmission. Manual — part 15
AJ-V8/5HP24
61
Engine Management
Variable Valve Timing
The ECM energizes the valve timing solenoids to
advance the intake valve timing and de-energizes
them to retard it.
The ECM uses engine load and speed maps to
decide when to advance and retard the timing.
The maps incorporate hysteresis for both engine
load and speed to prevent "hunting".
Between 1250 and 4500 RPM (nominal), at
engine loads greater than approximately 25 % of
the maximum, the timing is advanced. At low
engine loads and at the two ends of the RPM
range, the timing is retarded.
System operation is inhibited at engine coolant
temperatures below -10˚C (14˚F). System
operation is monitored using the input from the
camshaft position sensor. If a fault is detected
the ECM defaults to the retarded (de-energized)
condition.
EGR System
The ECM operates the 4 pole stepper motor in
the EGR valve to control the recirculation of
exhaust gases. Unlike previous systems, there
are no temperature or position feedback signals
from the valve. The ECM monitors EGR operation
using changes of mass air flow.
Engine Starting
At ignition on, if the gear selector is in Park or
Neutral, the ECM enables the fuel injection and
ignition functions. It also outputs a hard wired
digital security acknowledge signal to the BPM to
enable engine cranking. While the engine cranks,
the BPM outputs a hard wired digital engine
cranking signal to the ECM, which employs
engine starting strategies for the duration of the
signal.
If the gear selector is not in Park or Neutral at
ignition on, the ECM inhibits the fuel injection and
ignition functions, and withholds the security
acknowledge signal to prevent cranking.
VARIABLE VALVE TIMING MAP
Engine Speed, RPM x 1000
Retarded
Advanced
Engine Load
1
2
3
4
5
6
7
303-135
AJ-V8/5HP24
62
Engine Management
H02S Heaters
The ECM energizes the heater elements of the
HO2S during engine warm-up to shorten the time
it takes for them to produce accurate outputs.
Instrument Cluster
The instrument cluster uses CAN messages from
the ECM to operate the trip computer,
tachometer, engine coolant temperature gauge
and the BRAKE, CHECK ENG and general
warning lamps.
Note:
The CHECK ENG lamp is commonly
known as the MIL.
A/C Compressor Clutch
Operation of the A/C compressor clutch is
controlled by the ECM, to prevent unnecessary
loads on the engine during unfavorable operating
conditions.
On receipt of an A/C request signal from the
A/CCM, the ECM immediately energizes the A/C
compressor clutch relay provided the engine is
not at idle speed, the coolant temperature is not
above 119˚C (246˚F) and the throttle valve is not
fully open. When the A/C compressor clutch relay
energizes, the relay output is sensed by the
A/CCM, confirming that the A/C compressor
clutch is engaged.
If the engine is at idle speed, the coolant
temperature is above 119˚C (246˚F) or the throttle
is fully open, the ECM outputs a load inhibit
signal to the A/CCM and delays energising the
A/C compressor clutch relay. At idle speed the
delay is only momentary (in the order of 50 ms)
while idle speed compensation is implemented,
after which the load inhibit signal is removed. At
coolant temperatures above 119˚C (246˚F) or with
a fully open throttle, the delay is for the duration
of the inhibiting condition.
Similarly, with the A/C compressor clutch relay
already energized, if the engine coolant
temperature exceeds 119˚C (246˚F) or the
throttle goes to fully open, the ECM de-energizes
the A/C compressor clutch relay and outputs the
load inhibit signal to the A/CCM until the
inhibiting condition is removed.
When the windshield heaters and/or the
backlight heater are requested on, the A/CCM
sends a screen request signal to the ECM.
Provided the engine is not at idle speed, the
coolant temperature is not above 119˚C (246˚F)
and the throttle valve is not fully open, the ECM
takes no action and the A/C control module
subsequently energizes the heaters.
If the engine is at idle speed, the coolant
temperature is above 119˚C (246˚F) or the throttle
is fully open, the ECM outputs the load inhibit
signal (the same one as used for the A/C
compressor clutch operation) to the A/CCM to
delay energising the heaters. At idle speed the
delay is only momentary while idle speed
compensation is implemented, after which the
load inhibit signal is removed. At coolant
temperatures above 119˚C (246˚F) or with a fully
open throttle, the delay is for the duration of the
inhibiting condition.
Similarly, with the heaters already energized, if
the engine coolant temperature exceeds 119˚C
(246˚F) or the throttle goes to fully open, the
ECM outputs the load inhibit signal to the A/CCM
and the heaters are de-energized until the
inhibiting condition is removed.
Radiator Cooling Fans
The ECM monitors inputs from the A/C single
and triple pressure switches, and from the ECT
sensor on the engine, to control the operation of
the two radiator cooling fans. Outputs from the
ECM control two relays contained in the radiator
fans module, to operate the fans in off, slow or
fast mode. In the slow mode the fans are
connected in series; in the fast mode the fans are
connected in parallel. Hysteresis in the
temperature and pressure switching values
prevents "hunting" between modes.
Windshield and Backlight
Heaters
AJ-V8/5HP24
63
Engine Management
To counteract the increase in engine coolant
temperature that occurs after the engine stops,
at ignition off:
•
if the fans are already on, the ECM keeps
them on for 5 minutes, or until the ECT
decreases to a pre-determined value,
whichever occurs first
•
if the fans are off, the ECM determines, from
ECT and intake air temperature inputs, if the
fans need to be switched on. If they do, it
switches them on for 5 minutes, or until the
ECT decreases to a pre-determined value,
whichever occurs first.
Radiator Fan Switching Points
Mode
Coolant Temperature, ˚C (˚F)
A/C System Pressure, Bar (psi)
On
Off
On
Off
Slow
90 (194)
86 (187)
12 (174)
8 (116)
Fast
97.5 (207.5)
93.5 (200.5)
22 (319)
17.5 (254)
Diagnostics
The ECM performs self test routines and
monitors engine functions, inputs and outputs to
ensure correct operation of the engine and the
engine management system. Hard wired inputs
and outputs are monitored for short and open
circuits, and sensor inputs are also monitored for
range.
Additional checks are run on the more critical
sensor inputs to ensure their validity. Some of the
more critical inputs have substitute or default
values which the ECM adopts if the input is
diagnosed as faulty.
Any faults detected are logged in the ECM
memory as DTC. The ECM also outputs engine
malfunction messages on the CAN and adopts a
default mode of operation. Most default modes
retain some degree of engine operation (limp
home).
The ECM also stores OBD II related DTC
detected by other control modules on the CAN.
Non-OBD II related DTC are retained in the
memory of the control module that detects the
fault.
To prevent false DTC being logged, the
monitoring of some inputs and engine functions
is inhibited while the vehicle is above a given
altitude:
•
at altitudes of 2438m (8000ft) and
above,the ECM inhibits diagnostics on:
EGR valve and EGR flow; EVAP valve and
EVAP purge flow; idle speed control; misfire
detection; catalytic converter efficiency.
•
at altitudes of 2652m (8700ft) and
above, the ECM also inhibits diagnostics on:
HO2S; MAFS; O2S.
AJ-V8/5HP24
64
Engine Management
Additional Input Checks
Input
Additional Strategy
Action, Substitute or DefaultValue
Accelerator pedal
Accelerator pedal position input 1 compared to
If one input fails, the input of the other
position (x 2) and
accelerator pedal position input 2.
two is used.
mechanical guard
Both accelerator pedal position inputs compared to
If two inputs fail, ECM adopts fixed
position
mechanical guard position input.
throttle mode.
Throttle position
1 compared to input 2.
If either input fails, ECM adopts
(x 2)
Input 1 compared to target value (target value
mechanical guard mode of operation.
depends on operating mode, eg. normal running,
cruise control, traction active).
Engine coolant
After engine start, checks that expected
If fault detected, uses substitute value
temperature
temperature increase occurs, then monitors for
derived from transmission oil
excessive temperature decrease.
temperature.
Mass air flow
Compares input with predicted air flow (derived
If fault detected, uses throttle angle as
from a map of throttle angle against engine speed).
load measurement.
Intake air
Monitors for too fast change of input and for fixed
If fault detected, uses a fixed intake air
temperature
input.
temperature of 50˚C (122˚F).
Default Modes
Mode
Effect
General
CHECK
Message
Warning
ENG
Lamp
Lamp (MIL)
Engine shutdown
Activates fuel cut-off to stop engine
Red
On
ENGINE FAULT
Fixed throttle
Fixed throttle valve angle of approximately 2.5˚
Red
On
ENGINE FAULT
set, producing maximum engine speed (unloaded)
of approximately 1200 RPM.
Mechanical guard
Engine speed increases as throttle valve goes to
Red
On
ENGINE FAULT
mechanical guard position; idle speed increases to
approximately 1400 RPM; full throttle available
Engine speed
Engine speed limited to 3000 RPM
Amber
On
ENGINE FAULT
limiting
Redundancy
Substitute or default value adopted; no noticeable
Amber
Off
ENGINE FAULT
difference in performance
Exhaust emission
Substitute or default value adopted; potential
None
On
None
difference in performance
Note:
In mechanical guard mode, fuel intervention smooths the transition from normal to default mode, to prevent sudden
acceleration of the vehicle. Also, fuel intervention limits idle speed. Without fuel intervention idle speed would be
approximately 2000 RPM and cause excessive shock loads on the transmission when shifting out of Park or Neutral.
When engine load increases, idle speed fuel intervention is progressively withdrawn.
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