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General Smog Check

Did the Smog Tech Clamp The Right EVAP Hose?

During the EVAP portion of my van's smog test (Ford Windstar) the smog technician clamped a EVAP hose, but I'm not sure if it was the right one. My van's EVAP canister is not visible. It seems the tech clamped the hose after the EVAP canister going into the firewall; the hose leading away from the engine to the gas tank, as opposed to the hose leading to the canister purge valve. This can't be right.


Actually, it sounds like your smog technician clamped the correct hose. Here's how the EVAP test works... All vehicle's have an EVAP hose which runs from the gas tank to the engine's charcoal canister. The charcoal canister is usually located in one of the far corners of the engine compartment. It is a black container filled with charcoal pellets that absorb fuel vapors. Not all charcoal canisters however are located in the engine compartment. Some vehicles manufactures have mounted their canisters closer to the vehicle's gas tanks in-order to maximize efficiency.

The EVAP test ensures that there are no leaks within the EVAP system. The technician must clamp the end of the hose leading to the canister from the gas tank, and pressurize the gas tank with Nitrous Oxide via the EVAP test machine. The EVAP test machine will then calculate the drop in pressure due to any leaks, if any leaks exist. Technically there should be very little drop in pressure once the gas tank is pressurized. If there is a pressure loss, the machine will fail the EVAP portion of the smog test.

The fix requires locating the leak and repairing the line. Depending on where the leak is located, this repair may be cheap or expensive.

posted by SmogTips Support 02-15-2017 08:55 AM

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