Emission Control System Service

Unit of Study Types and Sources of Emissions Vapor Control Systems Improvement of Combustion Treating Exhaust Gas Measuring Exhaust Emissions Diagnostics

Three Major Pollutants Hydrocarbons (HC) un-burnt gasoline. Carbon monoxide (CO) partially burnt gasoline. Oxides of Nitrogen (NOx) air burns against itself.

Evaporation from the fuel tank. Blow-by gases which escape from the crankcase. Tail pipe emissions. Carburetor evaporation from the float bowl on old cars.

Three Ways to Control Pollution Improve combustion B. Capture the vapors and re-burn them. C. Treat the exhaust.

Vapor Control System Service

Positive Crankcase Ventilation (PCV)

Regulating the PCV Vapor Flow Amount Condition Manifold Vacuum Blow-by Gases Idle High Small Volume High Speed Low Vacuum Large

PCV Valve The PCV valve has two functions: 1. To regulate the amount of vapor entering the intake manifold at various engine speeds. 2. Prevent damage from backfire.

PCV Valve at Idle Speed Idle speed

PCV Valve at Cruising Speed

PCV Valve during BACKFIRE or when the Engine is OFF.

PCV Service Replace PCV valve every 30,000 miles. Clean the breather filter if applicable. The valve can be cleaned also if you don’t want to replace it. Inspect hoses for proper routing and deterioration. Check the air cleaner housing for oil build up. Check PCV system function. 1) Use the PCV vacuum tester. 2) Use the tachometer and look for RPM drop.

PCV Trouble-Shooting Notes Defective PCV system can cause big time vacuum leaks. This can lead to a very fast idle speed or stalling. If the valve or hoses get clogged the vapors back-up into the air cleaner clogging it too and puts oil in the air cleaner housing. A strange problem is if a valve cover gasket starts leaking oil winds up in the air cleaner also.

Oil in Air Cleaner Housing Gasket leaks mess up the vacuum on a PCV system. Manifold sucks air though the leaking gasket and the blow-by backs-up into the air cleaner.

Fuel Tank Evaporative Controls Captures HC evaporation from the fuel tank. Seals the gas tank and store the vapors in a charcoal canister. Vapor are purged to the intake manifold when the engine is running.

Older Style Evap 5) PCM controls flow to manifold 6) Vapor burns in cylinders 4) Intake vacuum draws vapor to manifold 3) Fresh enters here mixes w/fuel vapor 1) Fresh air enters here 2) Fuel vapor moves to canister

OBDII Evap 1 Vapor management valve. Closed when engine is off. Pulsed when engine is running. Fresh air vent controlled by the PCM. Closed when engine is off. Open while engine is running. PCM monitors pressure in fuel tank. Can cause DTC.

OBDII Evap Test Mode System can be tested for leaks. VMV closed Special device pumps nitrogen into system to check for leaks. CVV closed

Evaporative Service Some charcoal canisters have a filter under them that needs to be replaced every 30,000 miles. Inspect the hoses for proper routing and deterioration. Check to gas cap. 1996 and newer cars can be tested for leaks in the system. Use the scan tool to check the status of the purge control solenoid or control valves.

Controlling Combustion System Services

Heated Air Intake Systems Warms-up inlet air around exhaust manifold. Enhances fuel evaporation for better combustion. Maintains a 120˚F air temp. 2 types: Vacuum operated and mechanical thermostat. Prevents throttle icing.

Engine COLD Warm air

Engine WARM Warm air Cold air

Engine HOT Cold air only

Heated Air Intake Service Inspect system for proper hose routing, hose condition and connections. Check vacuum diaphragm for proper operation. Check blend door for proper movement. Check thermostat for proper operation.

Early Fuel Evaporation (EFE) Helps engine warm-up faster. Uses exhaust gas to warm intake manifold. Uses a special passageway under the intake manifold called a crossover. Use mostly on carbureted and throttle body Vee engines. A control valve forces the exhaust gas from one bank to the other. Only operates during the first 5 minutes or so of operation.

Heat Riser & EFE Valves Old Heat Riser valves used a bi-metal thermostatic spring to open and close the valve. EFE Valve was vacuum operated and was controlled by a TVS.

Heat Riser (EFE) Service Check exhaust valve for freedom of movement. Check vacuum diaphragm for proper operation. Check vacuum hoses for proper routing, condition and connections.

Exhaust Gas Recirculation (EGR) Intake manifold EGR valve System allows exhaust gas (water vapor) to flow from the exhaust manifold to the intake manifold. This cools the fuel mixture and reduces NOx emissions. Transfer tube Exhaust manifold

Cooling the Air/Fuel Mixture Combustion Gases Combustion Gases Water Vapor 3000º F 2500° F Cooling the combustion prevents formation of NOx emissions.

EGR Valve Convention vacuum diaphragm style. Back-pressure diaphragm type. Electronic (solenoid) From exhaust To intake manifold

EGR Controls EGR not necessary when the engine is cold or idling. Since NOx forms only from excessive combustion chamber temperatures.

EGR Service Checking valve for proper operation. Inspect hoses for proper routing, condition and connections.

TREATING EXHAUST GAS Air Injection Systems Catalytic Converters 1

Catalytic Converter Converts HC, CO, NOx into H²0, CO², O² & N² Uses rare metals to create a catalytic action. What is a catalyst? Single bed or two-way converters. Dual bed or three-way converters.

Single bed Older GM style Most common construction

Three Types of Converters Air injection tube Two way converter. (Single bed) Three-way converter. (Dual bed) Three-way converter with/air. flow Oxidation catalyst Reduction catalyst

Typical Three-Way Converter Reduction Catalyst NOx reduction Oxidation Catalyst Burns CO & HC

Testing Catalytic Converters Visual inspection on hoist. Check heat shields, air pipes pipe integrity. Mallet test for loose substrate. Exhaust back-pressure test. Temperature drop test using a pyrometer. Cat test using the Gas Analyzer.

Air Pump or Air Injection Systems Pumps fresh air into the exhaust manifold to burn up any HC or CO still present in the exhaust. Acts as an after burner. Needs several control valves for the system to function properly.

Basic Parts Air Pump Hoses Diverter Check valves Metal injection tubing

Air Pump Belt driven vane pump. Pumps fresh air into the exhaust manifold or the catalytic converter.

Diverter Valve The engine will backfire on deceleration if air is pumped into the exhaust manifold. The diverter valve sends the air back into the atmosphere during decel.

Diverter Normal Driving

Diverter During Decel

One-Way Check Valve Prevents damage to system in case of a backfire. Allow air to flow into the exhaust manifold. Blocks exhaust from going back toward air pump.

Air Switching Valve Used on air management systems that integrate the air injection system and the catalytic converter. Simply changes air from being pumped into the exhaust manifold to the converter.

Air Management System Air Pump Engine cold

Air Management Engine warmed-up

Measuring Exhaust Emissions 4 Gas Analyzer HC, CO, CO2, O2 5 Gas Analyzer HC, CO, CO2, O2, NOx

EPA EMISSION STANDARDS 1968-1971 HC 900 ppm CO 9.0% 1972-1974 HC 800 ppm CO 8.0% 1975-1979 HC 700 ppm CO 7.0% 1980 HC 300 ppm CO 3.0% 1981- on HC 220 ppm CO 1.2% I.M. 240 Test