Evaporative Emissions System: Testing and Inspection

Canister Purge Operation (Typical):

SYSTEM SERVICE

Ensure all vacuum hoses and electrical wires are routed clear of the exhaust manifold to prevent deterioration due to the high temperature. Vacuum hoses should always be a minimum of three inches from the exhaust manifold. When replacing the charcoal canister, mark then disconnect vacuum hoses from charcoal canister to ensure proper installation.

NOTE: Use only fuel resistant hoses when servicing the evaporative control system.


ROLLOVER AND PRESSURE RELIEF VALVE

These vehicles are equipped with only one [1][2]rollover/pressure relief valve. These dual function valves relieve fuel tank pressure and prevent fuel flow through the fuel tank vent lines should the vehicle be rolled over. The valve consists of a plunger, spring, and an orifice and guide plate. The valve is normally open. When fuel comes in contact with the valve, force applied by spring pressure seats the plunger against the guide plate, shutting off the flow of fuel vapor from the fuel tank to the evaporative canister. When fuel does not reach the valve, the spring pressure is overcome and the plunger moves away from the guide plate allowing fuel vapor to flow through the valve orifice.

In vehicle rollover the valve is inverted. In this position the plunger is forced against the guide plate and raw fuel is prevented from flowing through the valve orifice into the fuel tank vent tube.


INSPECTION PROCEDURES

A faulty evaporative emission control system on this vehicle can be diagnosed with a thorough inspection and the following basic tests.

1. Inspect fuel and vapor hoses for proper routing, cracks, or restrictions.
2. Inspect fuel tank cap for proper seal and fit.
3. Inspect Air Cleaner Venturi for damage or blockage.
4. Remove fuel tank vent hose from EVAP Canister. Apply light air pressure (3-6 psi.) to the Fuel tank filler tube. Air flow should be present at fuel tank vent hose. If air flow is not present, and Fuel Tank is not over-full, replace Pressure/Relief Rollover Valve.
5. Check Charcoal Canister for fuel saturation. If saturated check operation of the Pressure/Relief Rollover Valve.


CHARCOAL CANISTER

The charcoal canister is a sealed service-free unit. [1]

[1] If Charcoal Canister is saturated with liquid fuel check for proper Pressure/Relief Rollover Valve operation.