Infiniti QX56 (Z62). Manual — part 515
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< SYSTEM DESCRIPTION >
[VK56VD]
SYSTEM
Homogeneous combustion is a combustion method that fuel is injected during intake process so that combus-
tion occurs in the entire combustion chamber, as is common with conventional methods.
As for a start except for starts with the engine cold, homogeneous combustion occurs.
MIXTURE RATIO FEEDBACK CONTROL (CLOSED LOOP CONTROL)
The mixture ratio feedback system provides the best air-fuel mixture ratio for driveability and emission control.
The three way catalyst (manifold) can better reduce CO, HC and NOx emissions. This system uses A/F sen-
sor 1 in the exhaust manifold to monitor whether the engine operation is rich or lean. The ECM adjusts the
injection pulse width according to the sensor voltage signal. For more information about A/F sensor 1, refer to
EC-21, "Air Fuel Ratio (A/F) Sensor 1"
. This maintains the mixture ratio within the range of stoichiometric
(ideal air-fuel mixture).
This stage is referred to as the closed loop control condition.
Heated oxygen sensor 2 is located downstream of the three way catalyst (manifold). Even if the switching
characteristics of A/F sensor 1 shift, the air-fuel ratio is controlled to stoichiometric by the signal from heated
oxygen sensor 2.
• Open Loop Control
The open loop system condition refers to when the ECM detects any of the following conditions. Feedback
control stops in order to maintain stabilized fuel combustion.
- Deceleration and acceleration
- High-load, high-speed operation
- Malfunction of A/F sensor 1 or its circuit
- Insufficient activation of A/F sensor 1 at low engine coolant temperature
- High engine coolant temperature
- During warm-up
- After shifting from N to D
- When starting the engine
MIXTURE RATIO SELF-LEARNING CONTROL
The mixture ratio feedback control system monitors the mixture ratio signal transmitted from A/F sensor 1.
This feedback signal is then sent to the ECM. The ECM controls the basic mixture ratio as close to the theoret-
ical mixture ratio as possible. However, the basic mixture ratio is not necessarily controlled as originally
designed. Both manufacturing differences (i.e., mass air flow sensor hot wire) and characteristic changes dur-
ing operation (i.e., fuel injector clogging) directly affect mixture ratio.
Accordingly, the difference between the basic and theoretical mixture ratios is monitored in this system. This is
then computed in terms of “injection pulse duration” to automatically compensate for the difference between
the two ratios.
“Fuel trim” refers to the feedback compensation value compared against the basic injection duration. Fuel trim
includes “short-term fuel trim” and “long-term fuel trim”.
“Short term fuel trim” is the short-term fuel compensation used to maintain the mixture ratio at its theoretical
value. The signal from A/F sensor 1 indicates whether the mixture ratio is RICH or LEAN compared to the the-
oretical value. The signal then triggers a reduction in fuel volume if the mixture ratio is rich, and an increase in
fuel volume if it is lean.
“Long-term fuel trim” is overall fuel compensation carried out over time to compensate for continual deviation
of the “short-term fuel trim” from the central value. Continual deviation will occur due to individual engine differ-
ences, wear over time and changes in the usage environment.
FUEL INJECTION TIMING
Sequential Direct Injection Gasoline System
PBIB2793E
SYSTEM
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< SYSTEM DESCRIPTION >
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Fuel is injected into each cylinder during each engine cycle accord-
ing to the ignition order.
STRATIFIED-CHARGE START CONTROL
The use of the stratified-charge combustion method enables emissions-reduction when starting the engine
with engine coolant temperature between 5
°
C (41
°
F) and 40
°
C (104
°
F).
FUEL SHUT-OFF
Fuel to each cylinder is shut-off during deceleration, operation of the engine at excessively high speed or oper-
ation of the vehicle at excessively high speed.
FUEL PRESSURE CONTROL
FUEL PRESSURE CONTROL : System Diagram
INFOID:0000000006217701
FUEL PRESSURE CONTROL : System Description
INFOID:0000000006217702
INPUT/OUTPUT SIGNAL CHART
JSBIA0407GB
JSBIA0315GB
Sensor
Input signal to ECM
ECM function
Actuator
Crankshaft position sensor
Engine speed
Fuel injection
& mixture ratio
control
High pressure fuel pump
Camshaft position sensor
Camshaft position
Fuel rail pressure sensor
Fuel rail pressure
Low fuel pressure sensor
Low fuel pressure
Engine coolant temperature sensor
Engine coolant temperature
Throttle position sensor
Throttle position
Accelerator pedal position sensor
Accelerator pedal position
Battery
Battery voltage
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< SYSTEM DESCRIPTION >
[VK56VD]
SYSTEM
SYSTEM DESCRIPTION
Low fuel pressure control
• The low fuel pressure pump is controlled by the fuel pump control module (FPCM) and pumps fuel according
to a driving condition. The pumped fuel passes through the fuel filter and is sent to the high pressure fuel
pump. FPCM controls the low pressure fuel pump, according to a signal from ECM as shown in the table
below.
• Low fuel pressure is adjusted by the fuel pressure regulator.
High fuel pressure control
• The high pressure fuel pump raises the pressure of the fuel sent from the low pressure fuel pump. Actuated
by the camshaft, the high pressure fuel pump activates the high pressure fuel pump solenoid based on a sig-
nal received from ECM, and adjusts the amount of discharge by changing the timing of closing the inlet
check valve to control fuel rail pressure.
COOLING FAN CONTROL
JSBIA0235GB
Conditions
Amount of fuel flow
Supplied voltage
After a laps of 1 second after ignition ON
OFF
0 V
• For 1 second after turning ignition switch ON
• Engine is running under low load and low speed conditions
Low
Approximately 8.5 V
• Engine cranking
• Engine coolant temperature is below 10
°
C (50
°
F)
• Engine is running under high load and high speed conditions
High
Battery voltage
(11 – 14 V)
Except the above
Mid
Approximately 10 V
SYSTEM
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COOLING FAN CONTROL : System Diagram
INFOID:0000000006217703
COOLING FAN CONTROL : System Description
INFOID:0000000006217704
INPUT/OUTPUT SIGNAL CHART
*1: The ECM determines the engine speed by the signals of crankshaft position and camshaft position.
*2: This signal is sent to ECM via the CAN communication line.
SYSTEM DESCRIPTION
• Based on a signal transmitted from each sensor, ECM calculates a target fan speed responsive to a driving
condition. In addition, ECM calculates a fan pulley speed according to an engine speed and transmits a cool-
ing fan request signal to IPDM E/R via the CAN communication line to satisfy the target fan speed. Then,
IPDM E/R transmits ON/OFF pulse duty signal to electrically-controlled cooling fan coupling.
The cooling fan speed sensor detects a cooling fan speed and transmits the detection result to ECM.
• ECM judges the start signal state from the engine speed signal and battery voltage.
ELECTRIC IGNITION SYSTEM
JSBIA0237GB
Sensor
Input signal to ECM
ECM function
Actuator
Crankshaft position sensor
Engine speed*
1
Cooling fan speed request
signal*
2
IPDM E/R
↓
Electrically-controlled cooling fan
coupling
Camshaft position sensor
Camshaft position
Engine coolant temperature sensor
Engine coolant temperature
Refrigerant pressure sensor
Refrigerant pressure
Intake air temperature sensor
Intake air temperature
Battery
Battery voltage
Combination meter
Vehicle speed signal*
2
BCM
A/C switch signal*
2
Cooling fan speed sensor
Cooling fan speed
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