"When we do exhaust analysis, we are being a detective.

We look at what came out of the exhaust and figure out what

could have happened before to create those emissions. What

happened in the combustion chamber, or before the combustion

chamber, to create these results?

We can use clues and patterns of exhaust readings to figure

out if we have a problem in one of the following areas:

Air/Fuel Ratio

 

Combustion

 

Ignition

 

Emission Control Device

Then we know where to start our diagnosis with visual and

functional tests.

Good Combustion:

Let's start by reviewing good combustion.

The idea is to properly burn up all the gasoline and not

have any "leftovers". Into the combustion chamber we put gasoline,

symbolized by 'HC' for hydrocarbons. These are combinations

of hydrogen and carbon atoms, organic matter from old dinosaurs

maybe? We also add lots of air, which contains oxygen, symbolized

by 'O2'. (Oxygen atoms feel more comfortable going around

in pairs.) Normal air is about 20.7% oxygen, and if your shop

smog machine doesn't show about this when reading the air

inside your shop, you could have a bad oxygen sensor in your

smog machine, or a serious problem with the air in your shop,

or the planet has a problem... Back to combustion. The air

we add to the combustion chamber is mainly nitrogen, about

78%. (No, that's not nitrous, but related.) This doesn't burn,

it just goes along for the ride and expands with the heat,

helping to push down the piston.

Coming out of the combustion chamber we have carbon dioxide,

water and nitrogen. The carbon dioxide is symbolized CO2.

(One carbon atom combined with two oxygen atoms) It's good,

in that plants like it and it doesn't hurt us, but too much

is blamed for global warming. The water is symbolized by H2O,

two hydrogen atoms combined with one oxygen atom. Did you

realize that for every gallon of gas we burn, the tailpipe

puts out about about a gallon of water? And then good combustion

also puts out all the nitrogen that came in.

Good combustion is simply put this way: HC + O2 + N2 =

H2O + CO2 + N2.

I leave out the numbers which show proportions. Most of you

know we want an ideal mixture of 14.7 pounds of air to ..."