Infiniti I35 (A33). Manual — part 173
Multiport Fuel Injection (MFI) System
DESCRIPTION
NHEC0014
Input/Output Signal Chart
NHEC0014S01
Sensor
Input Signal to ECM
ECM func-
tion
Actuator
Crankshaft position sensor (POS)
Engine speed
Piston position
Fuel injec-
tion & mix-
ture ratio
control
Injectors
Camshaft position sensor (PHASE)
Mass air flow sensor
Amount of intake air
Engine coolant temperature sensor
Engine coolant temperature
Heated oxygen 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
Vehicle speed (From combination meter)
Vehicle speed
Ignition switch
Start signal
Air conditioner switch
Air conditioner operation
Knock sensor
Engine knocking condition
Battery
Battery voltage
Absolute pressure sensor
Ambient air barometric pressure
Power steering pressure sensor
Power steering operation
Heated oxygen sensor 2*
Density of oxygen in exhaust gas
*: This sensor is not used to control the engine system under normal conditions.
Basic Multiport Fuel Injection System
NHEC0014S02
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 and the mass air
flow sensor.
Various Fuel Injection Increase/Decrease Compensation
NHEC0014S03
In addition, the amount of fuel injected is compensated to improve engine performance under various oper-
ating conditions as listed below.
<Fuel increase>
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During warm-up
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When starting the engine
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During acceleration
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Hot-engine operation
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When selector lever is changed from N to D
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High-load, high-speed operation
<Fuel decrease>
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During deceleration
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During high engine speed operation
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ENGINE AND EMISSION BASIC CONTROL SYSTEM DESCRIPTION
Multiport Fuel Injection (MFI) System
EC-33
Mixture Ratio Feedback Control (Closed loop control)
NHEC0014S04
SEF336WC
The mixture ratio feedback system provides the best air-fuel mixture ratio for driveability and emission con-
trol. The three way catalyst (manifold) can then better reduce CO, HC and NOx emissions. This system uses
a heated oxygen 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
the heated oxygen sensor 1, refer to EC-247. This maintains the mixture ratio within the range of stoichiomet-
ric (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 the heated oxygen sensor 1 shift, the air-fuel ratio is controlled to stoichiometric by the sig-
nal from the heated oxygen sensor 2.
Open Loop Control
NHEC0014S05
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.
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Deceleration and acceleration
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High-load, high-speed operation
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Malfunction of heated oxygen sensor 1 or its circuit
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Insufficient activation of heated oxygen sensor 1 at low engine coolant temperature
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High engine coolant temperature
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During warm-up
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After shifting from N to D
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When starting the engine
Mixture Ratio Self-learning Control
NHEC0014S06
The mixture ratio feedback control system monitors the mixture ratio signal transmitted from the heated oxy-
gen 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., 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 the heated oxygen sensor 1 indicates whether the mixture ratio is RICH or LEAN com-
pared 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.
ENGINE AND EMISSION BASIC CONTROL SYSTEM DESCRIPTION
Multiport Fuel Injection (MFI) System (Cont’d)
EC-34
Fuel Injection Timing
NHEC0014S07
SEF179U
Two types of systems are used.
Sequential Multiport Fuel Injection System
NHEC0014S0701
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
NHEC0014S0702
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 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
NHEC0014S08
Fuel to each cylinder is cut off during deceleration or operation of the engine at excessively high speeds.
Electronic Ignition (EI) System
DESCRIPTION
NHEC0015
Input/Output Signal Chart
NHEC0015S01
Sensor
Input Signal to ECM
ECM func-
tion
Actuator
Crankshaft position sensor (POS)
Engine speed
Ignition tim-
ing control
Power transistor
Camshaft position sensor (PHASE)
Piston position
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
Vehicle speed (From combination meter)
Vehicle speed
Ignition switch
Start signal
Knock sensor
Engine knocking
Park/neutral position (PNP) switch
Gear position
Battery
Battery voltage
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ENGINE AND EMISSION BASIC CONTROL SYSTEM DESCRIPTION
Multiport Fuel Injection (MFI) System (Cont’d)
EC-35
System Description
NHEC0015S02
SEF742M
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. This data forms the map shown.
The ECM receives information such as the injection pulse width and camshaft position sensor signal. Com-
puting 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.
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At starting
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During warm-up
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At idle
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At low battery voltage
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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
DESCRIPTION
NHEC0016
Input/Output Signal Chart
NHEC0016S01
Sensor
Input Signal to ECM
ECM function
Actuator
Air conditioner switch
Air conditioner ON signal
Air conditioner cut
control
Air conditioner relay
Throttle position sensor
Throttle valve opening angle
Crankshaft position sensor (POS)
Engine speed
Engine coolant temperature sensor
Engine coolant temperature
Ignition switch
Start signal
Vehicle speed (From combination meter)
Vehicle speed
Refrigerant pressure sensor
Refrigerant pressure
Power steering pressure sensor
Power steering operation
System Description
NHEC0016S02
This system improves engine operation when the air conditioner is used.
Under the following conditions, the air conditioner is turned off.
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When the accelerator pedal is fully depressed.
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When cranking the engine.
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At high engine speeds.
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When the engine coolant temperature becomes excessively high.
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When operating power steering during low engine speed or low vehicle speed.
ENGINE AND EMISSION BASIC CONTROL SYSTEM DESCRIPTION
Electronic Ignition (EI) System (Cont’d)
EC-36
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