Fuel Evaporation System GMC S15 Pickup

DESCRIPTION

All Light and some Heavy Duty emissions models are equipped with an Evaporative Emission Control System (EECS), designed to prevent raw fuel vapors from escaping to the atmosphere. System consists of special fuel tank with expansion section; venting system which allows only vaporous fuel to be drawn into the system; pressure-vacuum relief valve in gas cap to control tank pressure; and vapor-storing charcoal canister.

OPERATION

During periods of engine operation, vapors are drawn through system vent lines and into intake manifold. When engine is off, fuel vapors are stored in charcoal of the vapor storage canister. Vapors are then drawn into intake manifold when engine is running again.

Canister purge solenoid is used on California models. It is controlled by the Electronic Control Module (ECM).

MAINTENANCE

No adjustments are required with this system. Check system and replace air inlet filter (if equipped) in bottom of charcoal canister, every 30,000 miles. Regular inspection of system components should be made and defective components replaced as necessary.

Vacuum Hose Routing for Single-Canister Evaporative Control System Canister must be lowest point in system. Scheme 13

BOWL VENT VALVE

1. Remove bowl vent vapor hose from carburetor. Check open condition of valve by connecting manual vacuum pump. It should not be possible to draw more than 0.5 in. Hg if valve is open (as when engine is off).
2. If high resistance or plugged system is found, check for plugged or restricted hose. Hose may be cleared with compressed air. If hose is clear, remove canister filter. If restriction persists, replace canister.
3. To check valve closed position, run engine at idle. Manifold vacuum will be applied to valve through control line. Bowl vent line should exhibit a plugged condition.
4. If valve is not closed, remove control vacuum line, and check for vacuum. If no vacuum, check for hose restriction or leak. Replace hose if required. If vacuum is present, replace canister assembly.

PURGE SOLENOID (CALIF.)

1. With ignition "ON" (engine stopped), ground test terminal and apply vacuum at carburetor side of purge solenoid. Vacuum pump should be able to produce 10 in. Hg. If not, remove connector from solenoid and connect test light between harness connector terminals.
2. If light comes on, faulty solenoid connections or solenoid is the cause. If no light, connect test light from each terminal of connector to ground.
3. If test light still does not come on, check for open wire to gage fuse. If test light does come on, check for grounded wire at ECM terminal "E" ("T" on Astro/Safari). If not grounded, check and/or replace ECM.
4. If requirements from step 1) are met, check to see if solenoid passes vacuum when test terminal is un-grounded (solenoid de-energized). It should open and keep pump from building up vacuum. If there is no vacuum drop, disconnect solenoid.
5. If there is still no drop after disconnecting solenoid, replace solenoid. If vacuum does drop after disconnecting solenoid, check for open wire to ECM terminal "E" ("T" on Astro/Safari). If OK, check and/or replace ECM.

PURGE VALVE (ON CANISTER)

1. Remove purge valve control vacuum line. Check for vacuum at line with engine running at approximately 1500 RPM. If there is no vacuum present, check EGR system.
2. Apply external vacuum to valve. Vacuum should hold. If not, replace canister assembly. If vacuum holds, remove purge line, and check for vacuum. If no vacuum, check PCV system.