Emission Control : Obtaining & interpreting scan tool data

Obtaining & interpreting scan tool data

Part 1. Preparation and safety

Objective

• Retrieve, record and clear stored OBD I & II diagnostic trouble codes using a scan tool.

Personal safety
Whenever you perform a task in the workshop you must use personal protective clothing and equipment that is appropriate for the task and which conforms to your local safety regulations and policies. Among other items, this may include:

• Work clothing - such as coveralls and steel-capped footwear
• Eye protection - such as safety glasses and face masks
• Ear protection - such as earmuffs and earplugs
• Hand protection – such as rubber gloves and barrier cream
• Respiratory equipment – such as face masks and valved respirators

Emission Control : Checking & cleaning a PCV valve

Checking & cleaning a PCV valve

Part 1. Preparation and safety

Objective

• Check and clean the PCV valve part of the emission control system.

Personal safety
Whenever you perform a task in the workshop you must use personal protective clothing and equipment that is appropriate for the task and which conforms to your local safety regulations and policies. Among other items, this may include:

• Work clothing - such as coveralls and steel-capped footwear
• Eye protection - such as safety glasses and face masks
• Ear protection - such as earmuffs and earplugs
• Hand protection – such as rubber gloves and barrier cream
• Respiratory equipment – such as face masks and valved respirators

Emission Control : On-board diagnostics

• OBD systems
• Diagnostic trouble codes
• Monitoring emissions

OBD systems

On-Board Diagnostic systems use the vehicle’s computers to detect problems with its emission components and other systems. It informs the vehicle operator when a fault occurs and assists the technicians in identifying and repairing malfunctioning circuits.

There are two different types of On Board Diagnostic systems. OBD 1, which operates under manufacturer standards and OBD 2, which operates under a standard set by the Society of Automotive Engineers.

OBD I is a system that identifies faults in the vehicle’s emission and powertrain.

It has been superseded by OBD II, an enhanced On-Board diagnostic system that identifies faults in the vehicle’s emission and powertrain and also tests the vehicles operational system to determine faults that do not affect the vehicles driveability but may affect its safety or emission efficiency.

Both systems provide a common standard that all vehicle manufacturers adhere to. This means that any generic OBD II compatible scan tool can access most vehicle data.

A scan tool is used to access the on-board diagnostic information, and the data link connector allows for the scanner to be connected to the car. This connector is a common size and shape and its location is also standardized, under the driver’s side of the instrument panel.

Emission Control

• Evaporation emission control
• Catalytic conversion
• Closed loop
• Regulated emissions
• Crankcase emission control
• EGR valves
• Controlling air-fuel ratios
• Charcoal storage devices

Evaporation emission control

Early vehicles vented the fuel tank through the filler cap into the atmosphere. Some of the fuel in the tank would vaporize. Some vapors escaped from the filler cap, some from the carburetter.
Non-vented filler caps are designed to stop the exit of vapors. A vacuum relief valve can relieve low pressure in the tank when the temperature drops. This will also stop the tank from collapsing if its internal pressure falls below atmospheric pressure.
The fuel cap may also incorporate a pressure relief valve. If the tank’s internal pressure exceeds the set value of the relief valve, it can stop the tank from rupturing. Some modern caps have no valves at all, and are completely sealed to stop the entry of air and water, as well as the emission of fuel vapor.

Emission Control : Types of emissions

• Hydrocarbons
• Hydrocarbons in exhaust gases
• Oxides of nitrogen
• Particulates
• Carbon monoxide
•  Carbon dioxide
• Sulfur content in fuels

Hydrocarbons

Gasoline, diesel, LP and natural gas are all hydrocarbon compounds.
Hydrocarbon emissions react with other compounds in the atmosphere to produce photo-chemical smog. Hydrocarbons are a major source of motor vehicle emissions.
Gasoline needs to evaporate easily to burn properly in an internal combustion engine. But this property also means it evaporates easily into the atmosphere at ordinary temperatures and pressures.
When a vehicle is being refuelled, hydrocarbon vapors can escape from the filler neck into the atmosphere. When the vehicle is left in the sun, its temperature increases, and fuel evaporates from the tank and, if there is a carburetter, from it as well.
An evaporation control system is fitted to modern vehicles to collect, and store the hydrocarbon vapors from the tank and the carburetter. Then, when conditions are suitable, these vapors are then drawn into the intake manifold, and burned, as part of the combustion process.
In a gasoline-engined vehicle, during an engine cycle, some of the gases escape past the piston rings into the crankcase. This is called blow-by. Some of these blow-by gases mix with heated, vaporized oil and can usually escape out into the atmosphere.
Modern vehicles direct these gases and vapors back through the inlet system to be burned during normal combustion.

Emission Control : Creation of emissions

• Sources of emission
• Combustion
• Combustion chamber design

Sources of emission

The term “emission” normally refers to the pollution produced by a light vehicle during normal use. Emission control systems are designed to limit the pollution caused by the harmful products of storing and burning fuel.
Emissions from a gasoline driven motor vehicle usually come from 4 sources:

• the fuel tank,
• the carburetter or fuel injection system,
• the crankcase,
• and the exhaust system.

The fuel tank and carburetter allow fuel to evaporate and escape to the atmosphere. These are called evaporative emissions.
The crankcase and exhaust system emit pollutants directly from the engine into the atmosphere. They are caused when hydrocarbons, lead compounds, and oxygen and nitrogen from the air, are burned in the combustion chamber.
In a compression-ignition engine, emissions originate from the engine, and escape to the atmosphere from the exhaust, and the crankcase breather.