Author Topic: Smog gurus  (Read 1688 times)

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Re: Smog gurus
« on: Jun 05, 2019, 10:46:39 AM »
The EVAP hose being pinched has nothing to do with the exhaust emissions. It's related to the Low Pressure Fuel Evaporative test which is used to ensure there are no leaks in the system up to the charcoal canister. Technically, they are not supposed to do that test while running the engine, but smog techs do it all the time.

Your numbers show you were running slightly lean at 2500 RPM, but an exhaust leak could also have been bringing in excess oxygen to skew those tailpipe numbers. At idle, you are very close to ideal air/fuel ratio. In short, the tech should have been running your truck for a longer period before checking emissions. The good thing is, if it had been too high, the machine would have forced him to do a "3-minute warm up" at 2500 RPM, then the numbers would have probably looked much better.

To check rich or lean status, enter your readings into one of these calculators:,engine_carbon%20balance,AFR%20calculations.htm


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