Boosted Engine EVAP Systems

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The EVAP system is designed to collect vapors produced inside the gas tank and consume those vapors in the engine. The purge function on an EVAP system requires a pressure differential between the intake manifold and the vent side of the evaporative system. On a non-boosted engine, manifold pressure is lower than the barometric pressure, causing fresh air to flow through the vapor canister and into the intake manifold. On a boosted engine, the manifold pressure can be greater than the barometric pressure, which would cause the fuel vapors to flow backward and pressurize the gas tank. In this On-Demand class we will cover three common methods of dealing with this problem which are: to use a purge pump, use a dual path system, or simply add a check valve in the purge line.