Infiniti QX56 (Z62). Manual - part 515

 

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Infiniti QX56 (Z62). Manual - part 515

 

 

EC-38

< 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

EC-39

< SYSTEM DESCRIPTION >

[VK56VD]

C

D

E

F

G

H

I

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EC

N

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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

EC-40

< 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

EC-41

< SYSTEM DESCRIPTION >

[VK56VD]

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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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