Nissan Silvia. Instruction — part 126
Mixture Ratio Feedback Control (Closed loop control)
NMEC0014S04
SEF336WA
The mixture ratio feedback system provides the best air-fuel mixture ratio for driveability and emission con-
trol. The warm-up three way catalyst can then better reduce CO, HC and NOx emissions. This system uses
a heated oxygen sensor 1 (front) in the exhaust manifold to monitor if 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
front heated oxygen sensor, refer to EC-152. 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.
Open Loop Control
NMEC0014S05
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 (front) or its circuit
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Insufficient activation of heated oxygen sensor 1 (front) 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
NMEC0014S06
The mixture ratio feedback control system monitors the mixture ratio signal transmitted from the heated oxy-
gen sensor 1 (front). 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 con-
trolled as originally designed. Both manufacturing differences (i.e., mass air flow sensor hot wire) and char-
acteristic 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 (front) 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.
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ENGINE AND EMISSION BASIC CONTROL SYSTEM DESCRIPTION
Multiport Fuel Injection (MFI) System (Cont’d)
EC-19
Fuel Injection Timing
NMEC0014S07
SEF337W
Two types of systems are used.
Sequential Multiport Fuel Injection System
NMEC0014S0701
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
NMEC0014S0702
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
NMEC0014S08
Fuel to each cylinder is cut off during deceleration or operation of the engine at excessively high speeds.
Electronic Ignition (EI) System
DESCRIPTION
NMEC0015
Input/Output Signal Chart
NMEC0015S01
Sensor
Input Signal to ECM
ECM func-
tion
Actuator
Camshaft position sensor
Engine speed and piston position
Ignition
timing con-
trol
Power transistor
Mass air flow sensor
Amount of intake air
Engine coolant temperature sensor
Engine coolant temperature
Throttle position sensor
Throttle position
Throttle valve idle position
Vehicle speed sensor
Vehicle speed
Ignition switch
Start signal
Knock sensor
Engine knocking
Park/neutral position (PNP) switch
Gear position
Battery
Battery voltage
ENGINE AND EMISSION BASIC CONTROL SYSTEM DESCRIPTION
Multiport Fuel Injection (MFI) System (Cont’d)
EC-20
System Description
NMEC0015S02
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
NMEC0016
Input/Output Signal Chart
NMEC0016S01
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
Camshaft position sensor
Engine speed
Engine coolant temperature sensor
Engine coolant temperature
Ignition switch
Start signal
Vehicle speed sensor
Vehicle speed
Power steering oil pressure switch
Power steering operation
System Description
NMEC0016S02
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.
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When engine speed is excessively low.
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ENGINE AND EMISSION BASIC CONTROL SYSTEM DESCRIPTION
Electronic Ignition (EI) System (Cont’d)
EC-21
Fuel Cut Control (at no load & high engine
speed)
DESCRIPTION
NMEC0017
Input/Output Signal Chart
NMEC0017S01
Sensor
Input Signal to ECM
ECM func-
tion
Actuator
Vehicle speed sensor
Vehicle speed
Fuel cut
control
Injectors
Park/neutral position (PNP) switch
Neutral position
Throttle position sensor
Throttle position
Engine coolant temperature sensor
Engine coolant temperature
Camshaft position sensor
Engine speed
If the engine speed is above 2,500 rpm with no load (for example, in neutral and engine speed over 2,500
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 operate until the engine speed reaches 2,000 rpm, then fuel cut is cancelled.
NOTE:
This function is different from deceleration control listed under “Multiport Fuel Injection (MFI) System”, EC-18.
Evaporative Emission System
DESCRIPTION
NMEC0018
SEF184NB
The evaporative emission system is used to reduce hydrocarbons emitted into the atmosphere from the fuel
system. This reduction of hydrocarbons is accomplished by activated charcoals in the EVAP canister.
The fuel vapor from sealed fuel tank is led into the EVAP canister when the engine is off. The fuel vapor is
then stored in the EVAP canister. The EVAP canister retains the fuel vapor until the EVAP canister is purged
by air.
When the engine is running, the air is drawn through the bottom of the EVAP canister. The fuel vapor will then
be led to the intake manifold.
When the engine runs at idle, the purge control valve is closed. Only a small amount of vapor flows into the
intake manifold through the constant purge orifice.
As the engine speed increases and the throttle vacuum rises, the purge control valve opens. The vapor is
sucked through both main purge and constant purge orifices.
ENGINE AND EMISSION BASIC CONTROL SYSTEM DESCRIPTION
Fuel Cut Control (at no load & high engine speed)
EC-22
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