Emission Controls and Fuel Economy

Emission control devices do more than help keep the environment clean.

Today’s high gasoline prices have raised awareness about vehicle fuel-saving tips such as: keeping the engine properly tuned, maintaining the correct tire pressure and avoiding hard acceleration and braking. Oftentimes, however, inspection of emission control devices is overlooked, as most of these components do not have a set service interval in the vehicle’s maintenance schedule.

Emission control devices on automotive internal combustion engines are designed to reduce major air pollutants such as Hydrocarbon (HC), Carbon Monoxide (CO) and Oxides of Nitrogen (NOx) while optimizing fuel economy and driveability. There are a number of emission components and subsystems that reduce pollution, but we’ll focus on a few that affect fuel economy when they malfunction.

O2 Sensors

Automotive oxygen sensors (O2 sensors) determine if the air-fuel ratio exiting a gasoline combustion engine is rich with unburnt fuel vapor or lean with excess oxygen. The sensor is part of an oxygen feedback system and is located in the exhaust path. The function of the sensor is to feed data to the Powertrain Control Module (PCM). The information is then used is to calculate the fuel injector pulse width to reduce emissions and help the engine run as efficiently as possible.

Once the O2 sensor reaches operating temperature, 572° to 662°F, the sensor generates a voltage that is inversely proportional to the amount of oxygen in the exhaust. When there is a large amount of oxygen in the exhaust caused by a lean condition, the sensor produces a low voltage. If the oxygen content is lower, caused by a rich condition, the sensor produces a higher voltage.

A faulty sensor delivers an incorrect signal to the PCM that will result in an air-fuel mixture that is too rich or too lean resulting in poor fuel economy. A symptom of a malfunctioning 02 sensor (in addition to the loss in fuel economy) would be an illuminated Malfunction Indicator Lamp (Check Engine light) or a vehicle failing a SMOG or emission test. Keep in mind that a number of conditions could cause a vehicle to fail an emission test or cause the MIL to illuminate; a faulty 02 sensor being one of them. A diagnostic scan tool would verify the diagnostic trouble code for a faulty O2 sensor.

EGR Valves

An EGR (Exhaust Gas Recirculation) valve is part of the emission control system that sends a controlled amount of exhaust gas into the intake manifold to dilute the incoming air-fuel mixture. This lowers peak combustion temperatures to help control NOx emissions.

A malfunctioning EGR valve can cause a significant reduction in fuel economy and a noticeable reduction in engine performance. If the valve leaks, expect rough idle and hesitation. If the valve is stuck closed, it can cause combustion temperatures to rise and lead to detonation. Both conditions contribute to poor fuel economy.

Catalytic Converters

Catalytic converters reduce the emissions of HC, CO and NOx. Normal vehicle miles or engine misfire can cause the catalyst or internal part of the converter to deteriorate. A meltdown of the ceramic core can cause a reduction of exhaust passage. This can increase vehicle emissions and deteriorate engine performance, driveability and fuel economy.

A vacuum or backpressure test will indicate if a restriction exists in the exhaust system. Be sure to inspect for blockage before replacing the catalytic converter(s).

Air Injection System (Smog) Pump

The Air Injection System (Smog) pump is an air compressor that injects additional air (oxygen) into the exhaust manifold to reduce exhaust temperatures and help burn off excess CO and HC gasses. There are two styles of smog pumps: engine driven (mechanical) or electric (DC powered). Some symptoms of a failing smog pump would be poor engine idle, increased NOx emissions and a failed emission test.

PCV valve

The Positive Crankcase Ventilation (PCV) or Crankcase Ventilation (CCV) (without vacuum control valve) emission systems help control HC emissions from the engine crankcase by removing blowby gases from the crankcase and directing them to the intake manifold. A crackcase that is not vented properly can result in oil dilution and sludge formation. In extreme circumstances, oil will collect in the air cleaner and restrict airflow in the filter element.

A malfunctioning PCV valve or clogged system can result in driveability problems, poor engine idle and increased fuel consumption. Chrysler recommends that the PCV valve be inspected and replaced at regular intervals. Refer to the owner’s manual maintenance schedule for the exact service interval.

EVAP System

Evaporative (EVAP) emission or fuel control system controls the evaporation of HC emissions. The system traps fuel vapors from the fuel tank and fuel injection system and redirects them into the intake manifold to be burned. In late model vehicles the PCM operates a purge solenoid that is used to shut off vacuum to the purge valve when the engine is not at operating temperature. If this valve is malfunctioning the canister will not purge properly resulting in driveability problems and a loss of fuel economy. The EVAP systems requires periodic inspection of hoses (replacement as needed) as they will deteriorate over time.

Keep your engine running clean and mean with Mopar emission control devices. See your Mopar Magazine dealer today.