Right mixture required

Oxygen sensors, catalytic convertor crucial to fuel economy

Paul Cole, Contributor

THERE IS a direct correlation between a vehicle's exhaust system and its fuel efficiency. When the fuel crisis hit the world in the 1970s, demand for fuel-efficient vehicles skyrocketed. Auto manufacturers responded with smaller cars which had more fuel-efficient vehicles. However, improvements could still be made and the fuel-injected engine replaced the older carburetted design.

Two additional parts were introduced to complement the new design, the oxygen sensor and the catalytic convertor. They are both a part of the exhaust system.

The oxygen sensor, or lambada sensor, is an electronic device that measures the proportion of oxygen in the gas or liquid being analysed. The catalytic convertor is a vehicle emission-control device which converts toxic by-products of combustion in the exhaust of an engine to less toxic substances, by way of a catalysed chemical reaction.

The efficiency of these two parts directly affect a vehicle's fuel efficiency. The engine is designed to mix air and fuel together, to be ignited and then move the pistons and crankshaft, which in turn moves the flywheel and axles. These then spin the wheels and propel the vehicle forwards or backwards, depending on the gear selected.

The optimum air-to-fuel ratio is 14.7 grams of air to one gram of fuel. Any mixture less than this is considered a rich mixture and anything more is lean.

Whenever the catalytic convertors are blocked or inefficient, the air-to-fuel ratio is altered and the vehicle runs rich, which means more fuel is burnt to cover the same distance.

Inefficiencies

Some symptoms of possible catalytic convertor inefficiency, or a rich burning vehicle, are lazy or sluggish acceleration from standstill, higher engine operating temperatures (oil and water) and poor fuel economy.

Therefore, the catalytic convertor should be replaced every five years or 50,000 miles (80,000 kilometres) and the oxygen sensors should be replaced every 10 years or 100,000 miles (160,000 kilometres).

However, sometimes the life span of these items is shortened, which usually triggers a check engine light (CEL) on the dashboard. The code will show that these items should be checked.

Paul Cole is managing director of King Midas Mufflers.