Nissan Altima (L32) 2007-2012 Service Manual: Multiport fuel injection system

System Diagram

System Description

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 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 operating 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 (CVT models) • 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 then better reduce CO, HC and NOx emissions. This system uses 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 A/F sensor 1, refer to EC-724, "DTC Logic". 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 (CVT models)

- 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 theoretical 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 during 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 theoretical 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.

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 four cylinders twice each engine cycle. In other words, pulse signals of the same width are simultaneously transmitted from the ECM.

The four 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, operation of the engine at excessively high speeds or operation of the vehicle at excessively high speeds.

Component Parts Location

1. Intake valve timing control solenoid valve

2. Ignition coil (with power transistor) and spark plug

3. Knock sensor, Crankshaft position sensor (POS)

4. Air fuel ratio (A/F) sensor 1

5. Camshaft position sensor (PHASE)

6. Engine coolant temperature sensor

7. Park/neutral position (PNP) switch

8. ECM

9. Refrigerant pressure sensor

10. Battery current sensor

11. IPDM E/R

12. Mass air flow sensor (with intake temperature sensor)

13. EVAP service port

14. Electric throttle control actuator (with built in throttle position sensor and throttle control motor)

15. EVAP canister purge volume control solenoid valve

16. Fuel injector

17. Power steering pressure sensor

1. Battery

2. Fuel pump fuse (15A)

3. IPDM E/R

4. Brake master cylinder

5. Engine ground

6. Air cleaner assembly

7. Mass air flow sensor (with intake air temperature sensor)

8. Radiator hose (upper)

9. Engine coolant temperature sensor

10. Intake air duct

11. Camshaft position sensor (PHASE)

12. Tie rod (RH)

13. Power steering pressure sensor

14. Knock sensor

15. Engine oil cooler

16. Crankshaft position sensor (POS)

17. Drive shaft (RH)

1. Exhaust manifold cover

2. Air fuel ratio (A/F) sensor 1

3. Heated oxygen sensor 2 (This illustration is a view from under vehicle.)

4. Engine oil pan

1. EVAP service port

2. Intake air duct

3. EVAP canister purge volume control solenoid valve

4. Intake manifold collector

5. Park/neutral position (PNP) switch (CVT) (This illustration is view with air cleaner assembly removed.)

6. Park/neutral position (PNP) switch (M/T) (This illustration is view with air cleaner assembly removed.)

7. Intake valve timing control solenoid valve (This illustration is view with engine removed.)

8. Exhaust manifold cover

9. Air fuel ratio (A/F) sensor 1

10. Air fuel ratio (A/F) sensor 1 harness connector

11. Heated oxygen sensor 2 (This illustration is view from under vehicle.)

12. Heated oxygen sensor 2 harness connector (This illustration is view from under vehicle.)

13. Engine oil pan

1. Throttle valve (This illustration is view with intake air duct removed.)

2. Electric throttle control actuator

3. Fuel injector harness connector

4. Condenser-2

5. Radiator hose (upper)

6. Battery

7. ECM

8. Fuel level sensor unit and fuel pump harness connector (This illustration is view with rear seat cushion and inspection hole cover removed.)

9. Fuel level sensor unit and fuel pump assembly

10. Fuel pressure regulator

11. Fuel tank temperature sensor

12. EVAP control system pressure sensor (This illustration is view with rear suspension member removed.)

13. EVAP canister vent control valve (This illustration is view with rear suspension member removed.)

14. EVAP canister (This illustration is view with rear suspension member removed.)

1. No.1 ignition coil

2. Cooling fan motor-1 harness connector

3. Cooling fan motor-2 harness connector

4. Refrigerant pressure sensor

5. Accelerator pedal position sensor

6. ASCD brake switch

7. Stop lamp switch

8. Brake pedal

9. ASCD clutch switch

10. Clutch pedal

11. ASCD steering switch

12. CANSEC switch

13. RESUME/ACCELERATE switch

14. SET/COAST switch

15. MAIN switch

Component Description