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Thursday, November 10, 2011

#38 - Driving Clean and Engine Exhaust Analysis – Part 1

According to the US Environmental Protection Agency, the personal automobile is the single greatest polluter because of the high numbers of vehicles on the road.* Various legislative initiatives since the early 1970’s have reduced the per-vehicle pollutant emissions. Some initiatives have addressed vehicle design while others have focused on maintenance-related emissions.

For example, in Ontario Canada, there is a vehicle inspection program that is intended to promote a reduction in automotive emissions. Vehicles must have an emissions test to renew registration and license plates. An overview of the program can be found at:

The tailpipe emissions inspection looks at Hydrocarbons, Carbon Monoxide, & Nitrogen Oxide (HC, CO, NO) while the engine is under load and while at idle. The allowable limits will depend on the type of vehicle and engine that is being tested.

I have a rather large pick-up truck. It recently failed the emissions test. Some of the gas readings were double what the emissions limit is. Not good. The culprit – leak in the exhaust manifold was allowing air into the engine. This caused the oxygen sensor to misread. This in turn caused a miscalculation the combustion mixture, making it fuel-rich. The result – high emissions. When my practical need for a pickup truck ceases very soon, I will likely purchase a much more sensible vehicle with lower emissions and better gas mileage.

However, it is also worth noting that an engine does not have to be large and powerful to produce high emissions. The graphics below are scans of actual test results obtained on various vehicles. Engine size and vehicle maintenance both have an affect on test scores. You will note that the small engine with the failed oxygen sensor produced high amounts of carbon monoxide, while the expertly maintained large engine had 0% carbon monoxide (probably less than 100ppm). Therefore, it can be said that good vehicle maintenance is demonstrably good for the vehicle and for the environment.

If a vehicle fails the test, the Ontario Drive Clean law says that the owner must fix the vehicle. The vehicle owner may obtain a ‘conditional pass’ if the problem has not been remediated after spending a fixed minimum of money on repairs. The test results shown at the bottom of the graphic met the requirements of a conditional pass.

In Ontario Canada, engine exhaust analysis is required to designate a vehicle ‘clean’ and keep it on the road. In a future post we will talk a little bit about another good reason to analyze engine exhaust gases.

If you are in the business of tuning engines or require analysis of engine exhaust, ask Mike or Dave about the 7460 Series Gas Analyzers.

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* U.S. ENVIRONMENTAL PROTECTION AGENCY, OFFICE OF MOBILE SOURCES (1994) Automobile Emissions: An Overview, EPA 400-F-92-007,

For additional information, please see the following links:

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