2004 INFINITI QX56 Factory Service Manual

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INFINITI QX56 2004 Factory Service Manual EC-26Revision: August 2007
ENGINE CONTROL SYSTEM
2004 QX56
Multiport Fuel Injection (MFI) SystemUBS00GZE
INPUT/OUTPUT SIGNAL CHART
*1: This sensor is not used to control the engine system under normal

EC-26Revision: August 2007
ENGINE CONTROL SYSTEM
2004 QX56
Multiport Fuel Injection (MFI) SystemUBS00GZE
INPUT/OUTPUT SIGNAL CHART
*1: This sensor is not used to control the engine system under normal conditions.
*2: This signal is sent to the ECM through CAN communication line.
*3: ECM determines the start signal status by the signals of engine speed and battery voltage.
SYSTEM DESCRIPTION
The amount of fuel injected from the fuel injector is determined by the ECM. The ECM controls the length of
time the valve remains open (injection pulse duration). The amount of fuel injected is a program value in the
ECM memory. The program value is preset by engine operating conditions. These conditions are determined
by input signals (for engine speed and intake air) from both the crankshaft position sensor (POS), camshaft
position sensor (PHASE) and the mass air flow sensor.
VARIOUS FUEL INJECTION INCREASE/DECREASE COMPENSATION
In addition, the amount of fuel injected is compensated to improve engine performance under various operat-
ing conditions as listed below.

During warm-up
When starting the engine
During acceleration
Hot-engine operation
When selector lever is changed from N to D
High-load, high-speed operation

During deceleration
During high engine speed operation
Sensor Input signal to ECM ECM function Actuator
Crankshaft position sensor (POS)
Engine speed*
3
Piston position
Fuel injection
& mixture ratio
controlFuel injector Camshaft position sensor (PHASE)
Mass air flow sensor Amount of intake air
Engine coolant temperature sensor Engine coolant temperature
A/F sensor 1 Density of oxygen in exhaust gas
Throttle position sensor Throttle position
Accelerator pedal position sensor Accelerator pedal position
Park/neutral position (PNP) switch Gear position
Knock sensor Engine knocking condition
Battery
Battery voltage*
3
Power steering pressure sensor Power steering operation
Heated oxygen sensor 2*
1Density of oxygen in exhaust gas
ABS actuator and electric unit (control unit)*
2VDC/TCS operation command
Air conditioner switch*
2Air conditioner operation
Wheel sensor*
2Vehicle speed

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INFINITI QX56 2004 Factory Service Manual ENGINE CONTROL SYSTEM
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MIXTURE RATIO FEEDBACK CONTROL (CLOSED LOOP CONTROL)
The mixture ratio feedback system provides the best air-fuel m

ENGINE CONTROL SYSTEM
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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 then better reduce CO, HC and NOx emissions. This system uses air
fuel ratio (A/F) sensor 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 air
fuel ratio (A/F) sensor 1, refer to EC-429
. 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 air fuel ratio (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 air fuel ratio (A/F) sensor 1 or its circuit
Insufficient activation of air fuel ratio (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., 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 long-term to compensate for continual deviation
of the short term fuel trim from the central value. Such deviation will occur due to individual engine differences,
wear over time and changes in the usage environment.
SEF 5 03 YB

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INFINITI QX56 2004 Factory Service Manual EC-28Revision: August 2007
ENGINE CONTROL SYSTEM
2004 QX56
FUEL INJECTION TIMING
Two types of systems are used.
Sequential Multiport Fuel Injection System
Fuel is injected into each cylinder during ea

EC-28Revision: August 2007
ENGINE CONTROL SYSTEM
2004 QX56
FUEL INJECTION TIMING
Two types of systems are used.
Sequential Multiport Fuel Injection System
Fuel is injected into each cylinder during each engine cycle according to the firing order. This system is used
when the engine is running.
Simultaneous Multiport Fuel Injection System
Fuel is injected simultaneously into all eight cylinders twice each engine cycle. In other words, pulse signals of
the same width are simultaneously transmitted from the ECM.
The eight injectors will then receive the signals two times for each engine cycle.
This system is used when the engine is being started and/or if the fail-safe system (CPU) is operating.
FUEL SHUT-OFF
Fuel to each cylinder is cut off during deceleration or operation of the engine at excessively high speeds.
Electronic Ignition (EI) SystemUBS00GZF
INPUT/OUTPUT SIGNAL CHART
*1: This signal is sent to the ECM through CAN communication line.
*2: ECM determines the start signal status by the signals of engine speed and battery voltage.
SYSTEM DESCRIPTION
The ignition timing is controlled by the ECM to maintain the best air-
fuel ratio for every running condition of the engine. The ignition tim-
ing data is stored in the ECM. This data forms the map shown.
The ECM receives information such as the injection pulse width and
camshaft position sensor signal. Computing this information, ignition
signals are transmitted to the power transistor.
e.g., N: 1,800 rpm, Tp: 1.50 msec
A °BTDC
During the following conditions, the ignition timing is revised by the
ECM according to the other data stored in the ECM.
At starting
During warm-up
PBIB0122E
Sensor Input signal to ECM ECM function Actuator
Crankshaft position sensor (POS)
Engine speed*
2
Piston position
Ignition timing
controlPower transistor Camshaft position sensor (PHASE)
Mass air flow sensor Amount of intake air
Engine coolant temperature sensor Engine coolant temperature
Throttle position sensor Throttle position
Accelerator pedal position sensor Accelerator pedal position
Knock sensor Engine knocking
Park/neutral position (PNP) switch Gear position
Battery
Battery voltage*
2
Wheel sensor*1Vehicle speed
SEF 7 42 M

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INFINITI QX56 2004 Factory Service Manual ENGINE CONTROL SYSTEM
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At idle
At low battery voltage
During acceleration
The knock sensor retard system is designed only for emergenci

ENGINE CONTROL SYSTEM
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At idle
At low battery voltage
During acceleration
The knock sensor retard system is designed only for emergencies. The basic ignition timing is programmed
within the anti-knocking zone, if recommended fuel is used under dry conditions. The retard system does not
operate under normal driving conditions. If engine knocking occurs, the knock sensor monitors the condition.
The signal is transmitted to the ECM. The ECM retards the ignition timing to eliminate the knocking condition.
Nissan Torque Demand (NTD) Control SystemUBS00GZG
INPUT/OUTPUT SIGNAL CHART
*1: Signal is sent to the ECM through CAN communication line.
SYSTEM DESCRIPTION
NTD control system decides the target traction based on the accelerator operation status and the current driv-
ing condition. It then selects the engine torque target by correcting running resistance and atmospheric pres-
sure, and controlling the power-train. Using electric throttle control actuator, it achieves the engine torque
development target which corresponds linearly to the driver's accelerator operation.
Running resistance correction control compares the engine torque estimate value, measured vehicle acceler-
ation, and running resistance on a flat road, and estimates vehicle weight gain and running resistance varia-
tion caused by slopes to correct the engine torque estimate value.
Atmospheric pressure correction control compares the engine torque estimate value from the airflow rate and
the target engine torque for the target traction, and estimates variation of atmospheric pressure to correct the
target engine torque. This system achieves powerful driving without reducing engine performance in the prac-
tical speed range in mountains and high-altitude areas.
Sensor Input signal to ECM ECM function Actuator
Camshaft position sensor (PHASE)
Crankshaft position sensor (POS)Engine speed
NTD controlElectric throttle con-
trol actuator and fuel
injector Mass air flow sensor Amount of intake air
Engine coolant temperature sensor Engine coolant temperature
Throttle position sensor Throttle position
Accelerator pedal position sensor Accelerator pedal position
Park/Neutral position (PNP) switch Gear position
Power steering pressure sensor Power steering operation
Battery Battery voltage
TCM (CAN communication) A/T control signal
Air conditioner switch*
1Air conditioner operation
ABS actuator and electric unit (control unit)*
1VDC/TCS/ABS operation
Wheel sensor*
1Vehicle speed
Electrical load*
1Electrical load signal

Page 1221 of 3371

INFINITI QX56 2004 Factory Service Manual EC-30Revision: August 2007
ENGINE CONTROL SYSTEM
2004 QX56
Air Conditioning Cut ControlUBS00GZH
INPUT/OUTPUT SIGNAL CHART
*1: Signal is sent to the ECM through CAN communication line.
*2: ECM determin

EC-30Revision: August 2007
ENGINE CONTROL SYSTEM
2004 QX56
Air Conditioning Cut ControlUBS00GZH
INPUT/OUTPUT SIGNAL CHART
*1: Signal is sent to the ECM through CAN communication line.
*2: ECM determines the start signal status by the signals of engine speed and battery voltage.
SYSTEM DESCRIPTION
This system improves engine operation when the air conditioner is used.
Under the following conditions, the air conditioner is turned off.
When the accelerator pedal is fully depressed.
When cranking the engine.
At high engine speeds.
When the engine coolant temperature becomes excessively high.
When operating power steering during low engine speed or low vehicle speed.
When engine speed is excessively low.
When refrigerant pressure is excessively low or high.
Fuel Cut Control (at No Load and High Engine Speed)UBS00GZI
INPUT/OUTPUT SIGNAL CHART
*1: Signal is sent to the ECM through CAN communication line.
SYSTEM DESCRIPTION
If the engine speed is above 1,400 rpm under no load (for example, the shift position is neutral and engine
speed is over 1,400 rpm) fuel will be cut off after some time. The exact time when the fuel is cut off varies
based on engine speed.
Fuel cut will be operated until the engine speed reaches 1,000 rpm, then fuel cut will be cancelled.
NOTE:
This function is different from deceleration control listed under Multiport Fuel Injection (MFI) System, EC-26
.
Sensor Input signal to ECM ECM function Actuator
Air conditioner switch*
1Air conditioner ON signal
Air conditioner
cut controlAir conditioner relay Throttle position sensor Throttle position
Accelerator pedal position sensor Accelerator pedal position
Crankshaft position sensor (POS)
Camshaft position sensor (PHASE)Engine speed*
2
Engine coolant temperature sensor Engine coolant temperature
Battery
Battery voltage*
2
Refrigerant pressure sensor Refrigerant pressure
Power steering pressure sensor Power steering operation
Wheel sensor*
1Vehicle speed
Sensor Input signal to ECM ECM function Actuator
Park/neutral position (PNP) switch Neutral position
Fuel cut control Fuel injector Accelerator pedal position sensor Accelerator pedal position
Engine coolant temperature sensor Engine coolant temperature
Crankshaft position sensor (POS)
Camshaft position sensor (PHASE)Engine speed
Wheel sensor*
1Vehicle speed

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INFINITI QX56 2004 Factory Service Manual ENGINE CONTROL SYSTEM
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CAN communicationUBS00GZJ
SYSTEM DESCRIPTION
CAN (Controller Area Network) is a serial communication line for real

Page 1223 of 3371

INFINITI QX56 2004 Factory Service Manual EC-32Revision: August 2007
BASIC SERVICE PROCEDURE
2004 QX56
BASIC SERVICE PROCEDUREPFP:00018
Idle Speed and Ignition Timing CheckUBS00GZK
IDLE SPEED
With CONSULT-II
Check idle speed in “DATA MONIT

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INFINITI QX56 2004 Factory Service Manual BASIC SERVICE PROCEDURE
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3. Check ignition timing.
Idle Speed/Ignition Timing/Idle Mixture Ratio AdjustmentUBS00GZL
PREPARATION
1. Make su

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