Emission Control Systems: Description and Operation

CRANKCASE EMISSION CONTROL SYSTEM
A closed ventilation system is used to prevent the escape of blow-by vapors to the atmosphere. The PCV valve includes a metered orifice which limits the flow of crankcase vapors into the intake manifold as determined by manifold vacuum. Under heavy acceleration or during high speed driving manifold vacuum may be too low for complete scavenging of blow-by gases. Under these conditions, some blow-by gasses are drawn into the air cleaner and then into the engine through the throttle valve.

CATALYTIC CONVERTOR
The catalytic convertor effectively changes harmful pollutants into carbon dioxide and water. The front convertor is a three-way type and the other is an oxidation catalyst.

EVAPORATIVE EMISSION CONTROL SYSTEM
A closed fuel tank ventilation system is used to prevent evaporative hydrocarbon emissions from escaping the fuel system into the atmosphere. Fuel tank vapors are contained in a carbon canister when the engine is off and vented to the intake manifold when the engine is running.

EXHAUST GAS EMISSION CONTROL SYSTEM
Exhaust gas emissions [carbon monoxide (CO), hydrocarbons (HC) and oxides of nitrogen (NOx)] are controlled by a combination of precise fuel metering, engine modifications, catalytic converter(s) and the addition of special control components. Combustion chamber design, intake manifold design and fuel and ignition system design all combine to reduce the level of exhaust emissions generated by the engine. Exhaust gas recirculation is used to reduce oxides of nitrogen emissions.

FILL PIPE RESTRICTOR
To prevent the introduction of leaded fuel to the system, a fillpipe restrictor is installed. This prevents the larger diameter fuel nozzles used for leaded fuels from entering the fillpipe. Leaded fuel will permanently contaminate the oxygen sensor, and the catalytic converter.

PULSED SECONDARY AIR INJECTION SYSTEM
The secondary air induction system leads air from the air cleaner directly into the exhaust so as to promote complete combustion of the exhaust gas in the front catalyst, lowering hydrocarbons (HC) and carbon monixide (CO).

HIGH ALTITUDE COMPENSATION SYSTEM (Non-California only)
The control unit calculates the altitude from the signal sent via the vacuum/pressure sensor. When the vehicle is driven in high altitude, the control unit energizes a control solenoid. The control solenoid then opens a passage, allowing air into the main air bleed of the carburetor, therby leaning out the mixture.

UP-SHIFT INDICATOR LIGHT (FWD M/T only)
The upshift indiactor lamp illuminates when the engine develops a certain amount of vacuum during acceleration. This prompts the driver to shift to the next higher gear. The purpose is to reduce engine rpm, therby reducing emissions.

FEEDBACK CARBURETOR
This is a system which controls A/F mixture before entering the converter.
When the oxygen contemt of the exhaust gas is small and the output voltage of the O2 sensor is larger than the "slice level", the control unit will determine that a rich condition exists.
In that condition, ther control unit continues to give control signals (electrical signals) to decrease the amount of control fuel to the duty solenoid valve. The A/F ratio becomes lean.
The amount of control fuel is determined by "Duty Ratio" which is defined as a percent of opening time of solenoid valve to one pulse cycle.
The slice level is an average voltagewhich has been calculated from peak-to-peak voltage of O2 sensor at the time.
When the oxygen content in the exhaust gas is large and the output voltage from the O2 sensor is smaller than the slice level, the control unit behave visa-versa. The A/F ratio becomes rich.
Under the following conditions, the control unit fixes the duty ratio to maintain good driving characteristics.
^ Cold engine temperature.
^ Heavy acceleration.
^ No O2 sensor output (cold sensor).