Exhaust Systems

Below we will cover the main components of an exhaust system, what each does and some common faults. Also, we’ll outline WOF law.

Components

Your exhaust has three main functions: To transfer poisonous gases to the rear of the car and away from the occupants To reduce noise To reduce emissions. The main components are as follows:

Exhaust Manifold
This is usually made of cast iron for extra strength and cost saving. It bolts up to the engine and exhaust gas from each cylinder is directed together into one or two pipes to be carried away through the rest of the exhaust system.

Catalytic Converter
These devices reduce toxic emissions by passing the exhaust gas through a ceramic honeycomb that has been very thinly coated with precious metals such as platinum or rhodium. The result is a transformation of harmful carbon monoxide and hydrocarbons to carbon dioxide and water. Oxides of nitrogen are also reduced to neutral nitrogen.

Muffler
The muffler is designed to reduce noise. There are many different types and designs available to carry out this requirement. Without a muffler, your car would be very loud and even unbearable to drive.

Exhaust Pipe
The exhaust pipe size and type of bends used will greatly affect the flow of gas through the exhaust and therefore the restriction posed by the exhaust and power developed by the engine.

Wherever press bend is used there is a reduction in the pipe diameter and therefore a restriction to flow. Mandrel bends are much better as they keep the correct diameter of the pipe throughout the bend increasing flow but they are more expensive to produce. Stock exhausts use press bends, aftermarket or performance exhausts use mandrel bends.

EGR System
The EGR System (Exhaust Gas Recirculation System) is designed to allow some exhaust gas back into the intake manifold, where it mixes with the air-fuel mixture and is re-burnt in the cylinders. This reduces emissions further by lowering combustion temperatures and pressures

O2 Sensor
The O2 sensor (Oxygen Sensor) reads the amount of Oxygen in the exhaust, it then sends a signal back to the Engine Management Computer, which adjusts the air-fuel mixture to maintain the optimum air-fuel ratio and therefore lower emissions. This can happen many times per second.

Common Faults

The most common fault seen with exhausts are leaks. A leak could be due to rust or corrosion, impact damage or poor mounting causing stress on a section of the exhaust and causing it to break or crack. If your exhaust has a leak it should be repaired as soon as possible as an exhaust leak will fail a WOF, could be letting harmful gas into the cabin and will be increasing emissions into the atmosphere.

Other faults include blocked catalytic converters, rattles inside mufflers due to loose parts, noise or vibration due to poor mounting or the exhaust touching a part of the car.

WOF Law

the LTSA requires all vehicles with an internal combustion engine to have an exhaust fitted, and the exhaust must be effective and in good working order.

Reasons for failure during a WOF check include: leaks, poor mounting, noise output noticeably and significantly louder than the original exhaust system (this is up to the inspector carrying out the WOF), visible smoke for 5 seconds or more when the engine is at idle, or visible smoke when the engine is being rapidly accelerated to a speed of 2500 rpm. These rules apply to petrol and diesel vehicles.