Several problems may arise in a catalytic converter as a result of an engine that is not tuned. When an engine works outside the correct specifications, unnecessary wear and damage may take place both in the catalytic converter and the engine itself. The damage is often the result of an incorrect air/ petrol mixture, an incorrect delay or advance in the ignition, a delay in the spark from the plug, etc. Any of these conditions may give rise to catalytic converter failure.

The petrol, which provides the power, must only be burned in the combustion chamber. Any petrol that leaves this chamber without having been burned will enter the exhaust system and may ignite inside the catalytic converter, due to the existing temperature. This may overheat the catalytic converter and cause fusion. Possible reasons for this are: incorrect mixture; incorrect delay or advance in the ignition; faulty spark plugs; faulty oxygen sensor (λ sensor); faulty injectors: faulty control valve, etc...

Oil or antifreeze reaching the exhaust system may obstruct passage through the catalytic converter by forming ash that impregnates its ceramic walls. These ash deposits give rise to two problems: first, they prevent the catalytic converter acting on the gas flow and secondly, since they obstruct the ceramic pores, an increase in back-pressure takes place and the heat and gases may even return to the engine. In this case, the engine may be receiving exhaust gases within the combustion chamber, thus reducing the performance of the following engine cycle. The result is a clear power loss and overheating of the engine components. Possible causes are: worn segments, worn valve seats, faulty joints, damaged engine components, etc...

Plugs that do not spark or spark badly causing unburned petrol to enter the exhaust system. Such petrol lights up within the catalytic converter due to the high temperature and gives rise to the total or partial fusion of the ceramic. The spark plugs and their wiring should be checked regularly and replaced if any damage or wear is detected.

A fault in the sensor gives an incorrect reading for the exhaust gases, which leads to it sending orders to the control unit to generate either a very rich mixture, which can lead to the ceramic melting, or a very poor mixture, leading to the vehicle failing to pass the Technical Inspection because the hydrocarbons will not be converted into harmless products on their passage through the catalytic converter.

The ceramic used in a catalytic converter is made of a fragile, light and very thin material. It is protected by a thick insulating band that holds the ceramic tightly in place and protects it from damage. However, sharp bumps or broken or badly secured supports within the exhaust system may fracture the ceramic . Once fractured, the ceramic becomes loose, blocking gas flow and increasing the back-pressure, which increases the engine temperature and reduces the power. In some cases, the ceramic pieces may break into tiny pieces and then be dragged along by the gases, leaving the catalytic converter empty.