Emission Control Systems: Description and Operation

1997 EVAPORATIVE EMISSIONS CONTROL SYSTEM
The evaporation control system prevents the emission of fuel tank vapors into the atmosphere. When fuel evaporates in the fuel tank, the vapors pass through vent hoses or tubes to an activated carbon filled evaporative canister. The canister temporarily holds the vapors. The Powertrain Control Module (PCM) allows intake manifold vacuum to draw vapors into the combustion chambers during certain operating conditions.

All engines use a duty cycle purge system. The PCM controls vapor flow by operating the duty cycle EVAP purge solenoid. Refer to Duty Cycle EVAP Purge Solenoid.

NOTE: The evaporative system uses specially manufactured hoses. they need replacement, only use fuel resistant hose. Also the hoses must be able to pass an Ozone compliance test.

FUEL TANK ROLLOVER VALVE
All vehicles have a rollover valve and pass a 360 1| rollover without fuel leakage. The valve also prevents fuel flow through the fuel tank vent valve hoses should the vehicle rollover.

The rollover valve is not a serviceable item.

EVAP CANISTER
All vehicles use a sealed, maintenance free, evaporative (EVAP) canister. Fuel tank pressure vents into the canister. The canister temporarily holds the fuel vapors until intake manifold vacuum draws them into the combustion chamber. The Powertrain Control Module (PCM) operates the canister through the EVAP purge solenoid. The PCM purges the canister at predetermined intervals and engine conditions.

EVAP Canister:

The canister mounts to a bracket that mounts to the frame rail near the right rear wheel. The canister protrudes through the top of the bracket. The vacuum and vapor tube connect to the top of the canister.

1997 DUTY CYCLE EVAP PURGE SOLENOID - PCM OUTPUT
The duty cycle EVAP purge solenoid regulates the rate of vapor flow from the EVAP canister to the throttle body. The Powertrain Control Module (PCM) operates the solenoid.

During the cold start warm-up period and the hot start time delay, the PCM does not energize the solenoid. When de-energized, no vapors are purged.

The engine enters closed loop operation after it reaches a specified temperature and the programmed time delay ends. During closed loop operation, the PCM energizes and de-energizes the solenoid 5 to 10 times per second, depending upon operating conditions. The PCM varies the vapor flow rate by changing solenoid pulse width. Pulse width is the amount of time the solenoid is energized.

Duty Cycle EVAP Purge Solenoid:

The EVAP purge solenoid and bracket attach to the right inner fender well next to the dash panel. The top of the solenoid has the word TOP on it. The solenoid will not operate unless it is installed correctly. If the vehicle has a 3.5L engine, the EVAP purge solenoid shares a bracket with the MTV solenoid.

EXHAUST GAS RECIRCULATION (EGR) SYSTEM
Injects a metered amount of exhaust gas into the intake manifold, lowering peak combustion temperatures. Lowering peak combustion temperatures inhibits the production of NOx. (Production of Oxides of Nitrogen (NOx) is greatest at combustion temperatures over 2300° F.)

AIR INJECTION SYSTEM
Adds air to burning exhaust gases in the catalytic converter, aiding the oxidation of Carbon Monoxide (CO) and Hydrocarbons (HC). This creates additional heat, which further accelerates catalytic converter operation.

CATALYTIC CONVERTER
Changes (converts) Carbon Monoxide (CO) and Hydrocarbons (HC) into Carbon Dioxide (CO2) and Water (H2O) in an oxidation reaction. Also converts Oxides of Nitrogen (NOx) into Oxygen (O2) and Nitrogen (N2) in a reduction reaction.

PRESSURE - VACUUM FILLER CAP

CAUTION: Remove the fuel filler cap to relieve fuel tank pressure. The cap must be removed prior to disconnecting any fuel system component or servicing the fuel tank.

Pressure Vacuum Filler Cap:

A pressure-vacuum relief cap seals the fuel tank. Tightening the cap on the fuel filler tube forms a seal between them. The relief valves in the cap are a safety feature. They prevent possible excessive pressure or vacuum in the tank. Excessive fuel tank pressure could be caused by a malfunction in the system or damage to the vent lines.

The seal between the cap and filler tube breaks when the cap is removed and relieves fuel tank pressure.

If the filler cap needs replacement, only use the correct part.

POSITIVE CRANKCASE VENTILATION (PCV) SYSTEMS

1997 PCV Valve:

Intake manifold vacuum removes crankcase vapors and piston blow-by from the engine. Emissions pass through the PCV valve into the intake manifold plenum. The vapors become part of the calibrated air-fuel mixture, are burned and expelled with the exhaust gases. The air cleaner supplies make up air when the engine does not have enough vapor or blow-by gases.

VEHICLE EMISSION CONTROL INFORMATION LABEL

Vehicle Emission Control Information (VECI) Label - Typical:

All models have a Vehicle Emission Control Information (VECI) Label. Chrysler permanently attaches the label in the engine compartment. It cannot be removed without defacing information and destroying the label.

The Label contains the vehicle's emission specifications and vacuum hose routings. All hoses must be connected and routed according to the label.