'87-95 5.0L MAP Vapor System with CANP
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The Evaporative Emission (EVAP) system prevents fuel vapor build-up in the sealed fuel tank. Fuel vapors trapped in the sealed tank are vented through the vapor valve assembly on top of the tank. The vapors leave the valve assembly through a single vapor line and continue to the EVAP canister (located in the engine compartment, in the rear of vehicle near luggage compartment area or along the frame rail) for storage until the vapors are purged to the engine for burning.
There are 2 types of Evaporative Emission (EVAP) systems: the Evaporative Emission (EVAP) Purge Flow system using a CANP from '87-95 with MAP EFI; the Vapor Management Flow system using a VMV from '94-96 with MAF EFI.
Physical damage, leaks, and missing items are the common causes of evaporative emission system faults. Fill cap damage or contamination that renders the pressure-vacuum valve inoperative may result in deformation of the tank. Care should always be exercised to make sure the fill cap is in working order.
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