Nissan Pathfinder. Manual - part 432

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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 position 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 drive ability 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-18, "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”.

PBIB3020E

SYSTEM

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“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 ignition 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.

ELECTRIC IGNITION SYSTEM
ELECTRIC IGNITION SYSTEM : System Description

INFOID:0000000009178038

SYSTEM DIAGRAM

*: ECM determines the start signal status by the signals of engine speed and battery voltage.

SYSTEM DESCRIPTION

Ignition order: 1 - 2 - 3 - 4 - 5 - 6

The ignition timing is controlled by the ECM to maintain the best air-fuel ratio for every running condition of the

engine. The ignition timing data is stored in the ECM.

SEF179U

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The ECM receives information such as the injection pulse width and camshaft position sensor (PHASE) sig-

nal. Computing this information, ignition signals are transmitted to the power transistor.

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

• 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.

AIR CONDITIONING CUT CONTROL
AIR CONDITIONING CUT CONTROL : System Description

INFOID:0000000009178039

SYSTEM DIAGRAM

*: 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.

AUTOMATIC SPEED CONTROL DEVICE (ASCD)

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AUTOMATIC SPEED CONTROL DEVICE (ASCD) : System Description

INFOID:0000000009178040

SYSTEM DIAGRAM

BASIC ASCD SYSTEM

Refer to Owner's Manual for ASCD operating instructions.

Automatic Speed Control Device (ASCD) allows a driver to keep vehicle at predetermined constant speed

without depressing accelerator pedal. Driver can set vehicle speed in advance between approximately 40 km/

h (25 MPH) and 144 km/h (89 MPH).

ECM controls throttle angle of electric throttle control actuator to regulate engine speed.

Operation status of ASCD is indicated by CRUISE indicator and SET indicator in combination meter. If any

malfunction occurs in the ASCD system, it automatically deactivates control.

NOTE:

Always drive vehicle in a safe manner according to traffic conditions and obey all traffic laws.

SET OPERATION

Press MAIN switch. (The CRUISE indicator in combination meter illuminates.)

When vehicle speed reaches a desired speed between approximately 40 km/h (25 MPH) and 144 km/h (89

MPH), press SET/COAST switch. (Then SET lamp in combination meter illuminates.)

ACCELERATE OPERATION

If the RESUME/ACCELERATE switch is pressed during cruise control driving, increase the vehicle speed until

the switch is released or vehicle speed reaches maximum speed controlled by the system.

And then ASCD will maintain the new set speed.

CANCEL OPERATION

When any of following conditions exist, cruise operation will be canceled.

• CANCEL switch is pressed.

• More than 2 switches at ASCD steering switch are pressed at the same time. (Set speed will be cleared.)

• Brake pedal is depressed.

• Selector lever is in the N, P, and R positions.

• Vehicle speed decreased to 13 km/h (8 MPH) lower than the set speed.

• TCS system is operated.

When the ECM detects any of the following conditions, the ECM will cancel the cruise operation and inform

the driver by blinking indicator lamp.

• Engine coolant temperature is slightly higher than the normal operating temperature, CRUISE lamp may

blink slowly.

When the engine coolant temperature decreases to the normal operating temperature, CRUISE lamp will

stop blinking and the cruise operation will be able to work by pressing SET/COAST switch or RESUME/

ACCELERATE switch.

• Malfunction for some self-diagnoses regarding ASCD control: SET indicator will blink quickly.

If MAIN switch is turned to OFF while ASCD is activated, all of ASCD operations will be canceled and vehicle

speed memory will be erased.

COAST OPERATION

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