Evaporative Emission Control System. Chevrolet Astro

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 1996 🢒 Astro - 2WD 🢒 Engine 🢒 Engine Controls - 4.3L (VIN W) 🢒 Evaporative Emission Control System

Evaporative Emission Control System System Description

Purpose

The Evaporative Emission (EVAP) control system limits the fuel vapors from escaping into the atmosphere. The EVAP transfers the fuel vapor from the sealed fuel tank to an activated carbon, charcoal, storage device or vapor canister. The canister stores the vapors until the engine is able to use the extra fuel vapor.

When the engine is able to use the extra fuel vapor, the intake air flow purges the fuel vapor from the carbon element. The normal combustion process then consumes the fuel vapor.

A fuel cap that is not normally vented to the atmosphere seals the fuel tank. The fuel tank cap has a safety valve which allows for both pressure and vacuum relief.

Operation


(1)	Purge Line
(2)	Vapor From Fuel Tank
(3)	Air

Purged fuel vapors flow into the EVAP canister tube labeled tank. The carbon absorbes the vapors. The intake air flow purges the canister when the engine is able to use the extra fuel vapor. A vacuum source applied to the EVAP canister tube labled purge draws fresh air through the the top of the canister. The air mixes with the fuel vapor. The combustion process consumes the mixture drawn into the intake manifold.

While the canister is purging, the system draws in fresh air through the air inlet at the top of the canister. The air flows to the bottom of the canister. The air forces the vapors out of the purge tube.

Evaporative Emission Control System Components

EVAP Canister Purge Solenoid

The EVAP system in some applications uses an electrically controlled solenoid in order to cycle the vacuum to the purge canister. The control module cycles the solenoid when the engine coolant temperature is greater than 45°C or the short term fuel trim cell is less than 122 counts.

EVAP Vacuum Switch

The system uses a vacuum switch in the purge line in order to detect when the system is being purged. The normally closed switch open when less than 1 in. Hg or more is present in the purge line.

The EVAP canister is located in the left rear fender well. If you need more information, refer to the Component Location.