The other day as I was going past a neighborhood auto repair place I saw the mechanic connecting a nitrogen thank to a car's fuel system.
He told me that it was to test the fuel system for leaks.
He was too busy to talk much but he said that California requires all vehicles built after 1994 to be tested.
I'm lucky, my vehicle is a '94 but I'm curious about the process.
What is being tested, how does the test work and when did they first require it?
Engineman
That is a pretty standard emissions test for the evaporative system. The system has to hold pressure and leakdown at a certain rate. They also test our gas caps for proper pressure holding up here in Canada.
The fumes from the gas tank and in my case carb float bowl need to be contained in some type of canister or activated charcoal when the vehicle sits and then the fumes get purged and burnt into the engine when it runs at speed.
Without this system working, the gas fumes are really bad around most vehicles, bad enough in a Jeep's case to get into our hair and clothes.
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 'New' frame in the works for '08. Some Canadian Bush Trip and Build Photos:
Sounds like he was using a smoke machine to test the EVAP system
Many states now have that as an emissions test. This test isn't what they do for inspection though, it is what a shop does to fix the problem in response to one of the myriad of trouble codes that pop up.
The nitrogen is used to make sure that you don't accidentally blow yourself up by putting enough oxygen (from shop air) into the fuel system to cause a problem. Then the smoke is turned on and at a VERY VERY low pressure and you run a few tests on the system. If you know what areas should leak, then you just look for the places that shouldn't be leaking. Like a rusted vent line, stuck purge solenoid, leaking vacuum line and such.
The inspection usually consists of a specialized code reader that they plug into the car, it looks for specific trouble codes. If they are found the vehicle fails. It also makes sure that all the onboard tests are run. Again if they are not run you fail. (some states allow a percentage of the tests to be not run as well) In addition some states also run a tailpipe test on a dyno to test the system for problems under load.
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