However, after 100k miles on the odometer, the numbers from the exhaust results do begin to deviate a little further from the average or recommended value.
Most smog check centers use a large rolling drum on the floor that spin your front tires (back tires for rear wheel drive). It can be used to determine the speed of your vehicle during a running simulation of the inspection process.
A current clamp is also attached to your 1st spark plug wire. This connection in concert with your rolling wheels can be used to measure the synchronization (or top dead center) between the signals from your spark plug and the revolutions at your wheels.
If the signals at your spark plugs skip or do not match with the expected angle of rotation at your wheels, the smog check process may be discontinued due to engine misfire or transmission issues. Troubleshooting the source of cylinder misfire or replacing a worn down clutch disc may be required before allowing the smog check to proceed.
If the spark plug signals and wheel rotation passes the 1st test, then the device inserted inside your car's exhaust pipe can proceed to measure the quantity of various types of gases released by your vehicle. The speeds are generally measured at 15 and 25 mph.
My vehicle above with 156k miles with white-colored smoke exhaust landed me on all categories as a gross polluter! A majority of the results exceeded the maximum values. Obviously, the smog certification didn't pass but I did have 30 days to fix the issue and return for another free inspection.
Before bringing the vehicle back in for another smog check analysis, it was important to understand what gases are produced and what can be done to reduce the harmful gases.
We all know that your air filter permits air through your intake manifold which includes mostly nitrogen and some oxygen. Further research surrounding the contents in gasoline fuel explain that it is a compound of mostly hydrocarbons, some nitrogen, and a little bit of other elements.
Combine these chemicals and gases with high voltage and you get the following bi-products that smog checks are most concerned about of which have been identified as harmful to us and our environment:
NO Nitrogen Oxide
CO Carbon Monoxide
With the use of an oxygen sensor, your car's computer can identify how much more fuel to dispense into your cylinders.
If the car detects high amounts of oxygen (lean), it means more fuel is required by extending the release of fuel through the fuel injectors.
If the car detects low amounts of oxygen (rich), it means less fuel is required thereby reducing the release of fuel through the fuel injectors.
Needless to say, a fast and operational oxygen sensor can greatly improve smog check results.
Though this doesn't completely eliminate all the harmful gases that exit your exhaust manifold, the 3-way catalytic converter is the final component that can and has been designed to help further reduce harmful gases.
Here are the new results after installing a new oxygen sensor and a new catalytic converter:
As the new numbers show, a new oxygen sensor, a new catalytic converter, and an engine warmed up to operating temperatures can greatly improve your chances for passing the smog check. That's impressive considering the car was labeled as a gross polluter last week!
So after 4 years and 30,823 miles one might be wondering what my numbers are like now. Well here you have it. Still passed smog check. However, the numbers appear to have shifted. Particularly the figures for Nitrogen Oxide (NO) at 15 mph.
When we calculate the ratio to fail for each test, we can see that both my HC and CO numbers have dropped but my NO figures has surged upward to values to be concerned about.
HC 98% ratio to fail
CO 44% ratio to fail
NO 65% ratio to fail
HC 62% ratio to fail
CO 14% ratio to fail
NO 96% ratio to fail
One pattern to recognize is that all of the results appear to do well when the O2 or Oxygen levels are low. Low oxygen output may mean good and complete combustion within the cylinders.
Also, note that during this smog test, I had installed new spark plugs and an air filter. Next time I may need to clean out the EVAP Canister to see if it will improve the NO numbers. Stay tuned for the next smog check results!