It stinks, but always fix a faulty catalytic converter quickly

Something I never knew...

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ROB MACGREGOR | Columnist profile | E-mail

Globe and Mail Update

Published Wednesday, May. 04, 2011 7:37PM EDT

Last updated Wednesday, May. 04, 2011 7:56PM EDT

Rob,

I have a 2004 Pontiac Sunfire 2.0 litre Ecotec. After the car warms up there is a rotten egg smell at the tailpipe. Otherwise the car runs well. No other problems.

Thanks for your time, Diane

Diane, you've just described the classic “rich fuel condition,” or over-fuelling. I’m surprised to hear that the car runs fine, because this symptom is usually combined with the following problems:

• Poor drivability

• Poor fuel economy

• Check engine light illuminated

I’m assuming that you have none of these issues and if that’s the case, your over-fuelling problem isn’t as critical as it could be.

That’s not to say that you don’t have a problem; you should have it checked by a repair shop that can perform onboard computer scanning – which by now is most reputable shops. A scan of your engine control module (computer) will tell a trained technician how much over-fuelling is going on as well as the possible problem.

Left unattended, this over-rich condition will eventually have you leaving a repair shop with an empty wallet.

What’s happening: Your car’s catalytic converter isn’t able to convert all of the unburned fuel and normal exhaust emissions into harmless gases as it should because of the over-fuelling problem.

These harmless gasses – mostly CO2, oxygen and water vapour – make up the majority of a vehicle’s tailpipe emissions. Under normal operating conditions, the “Cat” emits very small amounts of sulphur dioxide, but in most cases, you can’t smell the sulphur.

However, when the catalytic converter isn’t able to convert all of the fuel, you get excessive sulphur dioxide emissions – and that rotten egg smell. Another nasty side effect is that the excess emissions are spitting out of the car’s tailpipe.

What you’ll soon be facing is a plugged and inoperable catalytic converter. This occurs because the reactions inside the Cat create heat, and if it is not controlled under normal operating conditions, the heat will reach a point that will melt the substrates that make up the interior reaction elements of the Cat.

If left to the point of plugging, the exhaust gases and heat can’t leave the engine, which will eventually lead to internal damage to the engine – on top of the damage to the catalytic converter.

Get it checked sooner than later Diane, your wallet will love you, the traffic following you will love you and you’ll be able to enjoy egg salad sandwiches again.