Nissan Maxima. Manual - part 390

EC-44

< SYSTEM DESCRIPTION >

[VQ35DE]

ENGINE CONTROL SYSTEM

PCV valve

EC-514, "Description"

Power steering pressure sensor

EC-386, "Description"

Power valves 1 and 2

EC-518, "Description"

Refrigerant pressure sensor

EC-515, "Description"

Stop lamp switch

EC-448, "Description"

TCM

EC-397, "Description"

Throttle control motor

EC-462, "Description"

Throttle control motor relay

EC-456, "Description"

Throttle position sensor

EC-207, "Description"

VIAS control solenoid valve 1

EC-442, "Description"

VIAS control solenoid valve 2

EC-445, "Description"

Component

Reference

MULTIPORT FUEL INJECTION SYSTEM

EC-45

< SYSTEM DESCRIPTION >

[VQ35DE]

C

D

E

F

G

H

I

J

K

L

M

A

EC

N

P

O

MULTIPORT FUEL INJECTION SYSTEM

System Diagram

INFOID:0000000010094801

System Description

INFOID:0000000010094802

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 via the CAN communication line.

JMBIA1534GB

Sensor

Input Signal to ECM

ECM function

Actuator

Crankshaft position sensor (POS)

Engine speed*

3

Piston position

Fuel injection 
& mixture ratio 
control

Fuel injector

Camshaft position sensor (PHASE)

Mass air flow sensor

Amount of intake air

Intake air temperature sensor

Intake air temperature

Engine coolant temperature sensor

Engine coolant temperature

Air fuel ratio (A/F) sensor 1

Density of oxygen in exhaust gas

Throttle position sensor

Throttle position

Accelerator pedal position sensor

Accelerator pedal position

TCM

Gear position

Battery

Battery voltage*

3

Knock sensor

Engine knocking condition

Power steering pressure sensor

Power steering operation

Heated oxygen sensor 2*

1

Density of oxygen in exhaust gas

ABS actuator and electric unit (control unit)

VDC/TCS operation command*

2

Unified meter and A/C amp.

Air conditioner operation*

2

Vehicle speed*

2

EC-46

< SYSTEM DESCRIPTION >

[VQ35DE]

MULTIPORT FUEL INJECTION SYSTEM

*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 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.

<Fuel increase>

• 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

<Fuel decrease>

• During deceleration

• During high engine speed operation

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-218, "Description"

. This maintains the mixture ratio within the range of stoichiometric (ideal air-fuel mix-

ture).

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

PBIB3020E

MULTIPORT FUEL INJECTION SYSTEM

EC-47

< SYSTEM DESCRIPTION >

[VQ35DE]

C

D

E

F

G

H

I

J

K

L

M

A

EC

N

P

O

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

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 six cylinders twice each engine cycle. In other words, pulse signals of

the same width are simultaneously transmitted from the ECM.

The six injectors will then receive the signals 2 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, operation of the engine at excessively high speeds or oper-

ation of the vehicle at excessively high speeds.

SEF179U