Wed10222014

On The Road

Sensors, computers help cars run cleaner


This marks the return of Matt Pataky as a monthly columnist for On the Road. He is the owner of Sunnyvale Foreign Car Service in Mountain View.

Man’s best friend is also the mechanics’ best friend at our shop. Ronin, the resident Golden Retriever, has been begging for apples and attention from customers since I first brought him to the shop five years ago.

If Ronin could write, here’s what he might have to say about his life at the shop:

I love going to the shop every day. Most days are pretty normal. I meet a lot of people, get massages, let kids pull my tail, learn about cars and, if I’m lucky, some unsuspecting customer won’t mind if I steal the apple out of his or her hand.

One thing I can never predict is what my master is going to talk about. Some days he talks about engines, fuel systems and fuel trims. The next day, he could be waxing philosophical on the check engine light, vehicle inspections and brakes.

Last week I learned more than I’ll ever need to know about lean air fuel (LAF) ratio sensors and O2 sensors. I am going to break this down for you in a way that hopefully earns me a free apple or 10-minute paw massage.

No manufacturer has been able to design an internal combustion engine that runs perfectly clean. With the help of sensors and computers, cars can become as clean as possible. The LAF will measure oxygen from +1.5 to -1.5 volts and the Zirconia O2 sensor measures oxygen from 0 to 1 volts. My master always gets Matt

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excited about the LAF sensors, as they can measure a much larger bandwidth of air and therefore have more data to make corrections.

The stoichiometric theory for perfect combustion is 14.7 parts of air to one part fuel. The LAF and Zirconia O2 sensors sample air in the exhaust system to measure how efficiently the engine is running. They make lean (negative) or rich (positive) corrections against the amount of air found in the exhaust system.

The sensors test the difference between the amount of oxygen in the exhaust gas and the amount of oxygen in the air. Rich mixture causes an oxygen demand, which enables the voltage to build up due to the transportation of oxygen ions through the sensor layer.

Lean mixture causes low voltage, because there is an excess of oxygen. For example, if the engine starts to misfire, extra air will be found in the exhaust system. The LAF then samples the amount of air and either adds or subtracts fuel. By doing this, the onboard computer can smooth out a car that is running rough or even shut down the problem cylinder by correcting within milliseconds. That way, the engine saves fuel and becomes more efficient. It also protects important exhaust components like catalytic converters and the engine itself.

Did you get that? If so, I’ll be expecting you to drop off some treats for me at the shop. If you want to learn more, my master is a tech geek who gets excited about this kind of stuff. Tell him I sent you – and don’t forget that apple.

Matt Pataky owns Sunnyvale Foreign Car Service, 83 Pioneer Way, Mountain View. For more information, call 960-6988, email This email address is being protected from spambots. You need JavaScript enabled to view it. or visit sfcarservices.com.

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