CATALYTIC CONVERTERS

At AC Autos - you can be assured that we are experts in this field. We have the latest exhaust gas analysis equipment and we supply a full range of over 3500 models. Our cats are vehicle specific, not the 'universal' type which means they fit correctly first time and match your vehicle's original specification.
Catalytic converters are part of your car's exhaust system which converts noxious gases from the car exhaust into Carbon Dioxide, Nitrogen and Water.

Frequently asked Questions (FAQ)

Q: Do I need to change my cat?
A: A catalytic converter can be an expensive item, so you don't want to change it unless it is absolutely necessary. We have the right tools and expertise to assure you of the condition of your catalytic converter.
Q: How do I know if my Cat is working?
A: Only in extreme cases of cat meltdown will a total blockage occur, you will know that something has gone wrong because the car will not run! But mostly, you will only find out when the car fails the emission test at the annual MoT.

How CATs work

If your car runs on petrol and was built after 1992, it will have a Cat (catalytic converter). It may even have one if dates from before 1992.
Environmental lobby pressure on Governments has forced them to legislate to attempt to limit potentially damaging emissions. The Cat is a device located in the exhaust system which converts unwelcome gases from the exhaust into harmless Carbon Dioxide - the same as we breathe out - Nitrogen, which forms 80% of air, and water vapour in the form of steam. It does this by passing the gases over a fine honeycomb (usually of metal) that is plated with precious metals such as platinum, palladium and rhodium. It is these metals that start the chemical reactions.

How we test your CAT

At AC Autos we have several ways of testing your Cat. We have invested in the latest technology so that you can be confident that our engineering report is accurate:

• Emissions test. As mentioned above, by measuring the car's emissions it is possible to tell from the readings that the cat has failed.
• Rattle test. If the 'honeycomb' inside has broken up, when the Cat is pounded with a fist, the rattling from inside gives the game away. (Don't try this yourself unless you are certain the Cat is cool enough to touch).
• Temperature. Using our specialised laser pyrometer (a thermometer used for measuring very hot temperatures), we spot check the inlet and outlet temperatures. The rear of a functioning Cat is much hotter than the front.
• Back pressure. We measure the exhaust back pressure to see if there are any blockages.

Reasons for CAT failure

All too often a garage will sell a new Cat to a customer without checking the underlying reason for the failure. We will NOT fit a new Cat to your car without first checking that it really needs it. If your Cat is then replaced by us, we check the reason for the failure and we offer expert advice to make sure the same problem does not recur.

• Wrong Fuel. Put simply, leaded fuel wrecks the Cat. It will soon get blocked and stop working.
• Faulty Oxygen (Lambda) Sensor. This device sits in the exhaust pipe and measures the amount of oxygen in the gases. If it is defective, in time, an over-rich mixture (too much fuel) will poison the Cat..
• Misfire. These are usually caused by a failure in the ignition system. Fouled spark plugs, broken-down ignition leads or cracked distributor caps cause the engine to 'stutter', this is usually the beginning of the cat's destruction. Every time the misfire happens, some unburnt petrol finds its way down the exhaust pipe. This fuel then poisons the cat as above.
• Fouled Injectors. Injectors spray finely controlled amounts of fuel into the engine in response to the demands of the driver. Certain inferior brands of fuel lack detergent and in time cause deposits to form on the injector nozzle. This prevents it from closing properly and can allow unwanted petrol to leak into the engine. This will eventually reach the Cat and poison it. See our Fuel Injection page for more details.
• Failed MAP sensor. The Manifold Air Pressure Sensor is one of the crucial engine management sensors; if it fails it will cause a rich mixture.
• Bump Starting the Car. If you attempt to bump start a car (with a run down battery) this has the same effect as a misfire. Unburnt fuel travels into the CAT and destroys the catalyst.