What exactly is the sniffer measuring?

Most people use a car to commute, and you may have had to deal with your vehicle’s smog check, and your own respiratory problems, possibly related to vehicle smog. Have you ever found yourself asking: “where is the closest station for smog check near me?”

HCs are essentially unburned fuel. When you hear about octane it’s often a reference to the anti-knock index at the pump (87 etc) but it is also a reference to the chemical composition of fuel, part of which is made from C8H18 (eight carbon atoms and 18 hydrogen atoms; hence octane). HC is measured in parts per million (ppm) by the sniffer.

When fuel (HC) and air (O2 + N2) are combusted the ideal product would be energy and water vapor (H20). Because the combustion process is imperfect, CO is one of the byproducts produced. CO is measured as a percentage of the exhaust gas. It is a colorless odorless gas and if you breathe it, it will combine with the hemoglobin in your blood and make you sick or kill you in larger doses. Running your engine in the garage is a great way to pass out and possibly die. After becoming aware of this dangerous effect, you may be asking yourself: “where is a station for smog check near me?”

CO is also used as an indicator of fuel mixture ratio. An ideal percentage of excess CO would be zero. In practice the %CO measured is a few percentage points: a fuel ratio the VW engine can burn efficiently in all climates, temperatures and conditions. For example, 1-2% would be a relatively lean fuel ratio for a VW especially fuel injected models; 10% is very rich (so much so that you can smell the unburned fuel from the exhaust pipe and see it collect on the ground if it has been raining).

NOx is produced when combustion chamber temperatures are high. It was once viewed as the #1 environmental enemy and largely responsible for the smog in the LA basin. At that time emission reducing devices were geared towards reducing it at the expense of other emissions. That was 20 years ago and since then scientists have come to understand that all the emissions are destructive especially CO2 (a harmful greenhouse gas). You may start wondering again, “where is that station for smog check near me?”

Unfortunately on a VW there is no simple way to minimize all three emissions at once like a modern car is able to do. Lower the HC and CO by leaning out the engine and you produce too much NOx and vice versa. Plus, the catalytic converter (which few air-cooled VW models are equipped with) can only do its job at the near perfect fuel ratio (theoretically ideal) which isn’t the best ratio for long life of an air-cooled engine.