Boosted Engine EVAP Systems

May 31, 2024

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.