What is the new "evap test" that is being required for my car to pass smog check?
Ever open your gas cap at the gas station on a hot day and hear a "whoosh" sound and smell the strong odor of gas? Your vehicle has an emission system which stores those vapors under pressure in hoses and a charcoal filled canister usually mounted in the engine compartment until the computer or other control device commands the movement of those vapors into the engine to be burned along with the gas supplied by the carb or injectors. Were those vapors to be let out into the atmosphere, the air would be further polluted and your fuel mileage would suffer.
Newer vehicles have an automatic monitoring system which measures the pressure created in the gas tank when the temp increases and "looks" using sophisticated sensors for the pressure being less than it expects for the conditions. When this occurs the computer will illuminate the "CHECK ENGINE" or "SERVICE ENGINE SOON" light on the dash to warn that a problem exists. On newer vehicles you should first check the tightness of the gas cap by turning it until you hear at least 3 "CLICKS".
Older vehicles (pre 1996) do not usually have such a monitoring system and will not alert when a vapor leak occurs. Since rubber seals and hoses deteriorate over time and when they do leak, you can lose up to a gallon of fuel per day. $4 a day or $28 a week up in the air and out of your pocket.
The EPA mandates cleaner air and California decided to implement a new testing procedure to identify and repair vapor leaking vehicles. This required a new expensive testing apparatus designed to replace the fuel vapors in the system with non flammable nitrogen vapor and build up a pressure in the system and then stop the vapor build. The machine then monitors the pressure loss and measures it against the norm.
When the test procedure was being field tested the "fail rate" was roughly 10% of all vehicles capable of being tested. Since the testing was required at this station that rate seems to be about what I'm experiencing and of course those vehicles are eligible for the State sponsored repair program mentioned elsewhere on this site.
