Fuel Evaporation System Honda Prelude II

DESCRIPTION

System prevents gasoline vapors from escaping into atmosphere from fuel tank and carburetor. All models use a pressure/vacuum relief fuel filler cap, purge control diaphragm valve, thermovalve, two-way valve, charcoal canister, and connecting lines and hoses.

Use an air vent cut-off solenoid valve, inner vent solenoid valve, power valve lock solenoid, thermosensor, power valve control solenoid, and control unit.

OPERATION

When fuel tank pressure exceeds a preset value, two-way valve opens and allows excess vapors to vent into canister. If excessive vacuum forms in fuel tank, two-way valve opens and outside air enters fuel tank through canister. Fuel filler cap acts as a safety valve if evaporation system fails.

Thermovalve closes and allows manifold vacuum to open purge control valve when engine coolant temperature exceeds set temperature.

When engine is not running, air vent cut-off solenoid valve opens outer air vent passage. This allows float bowl vapors to vent into canister. When engine is running above 500 RPM, air vent cut-off solenoid valve and inner vent solenoid valve open float bowl inner and sub-inner air vent passages to air cleaner. On hot engine starts, when coolant temperature is above 158°F (70°C), delay timer delays opening of inner air vent passage to ease hot engine start up.

MAINTENANCE

Inspect system, hoses, and connections. Test all components every 60,000 miles or every 5 years.

THERMOVALVE & PURGE CONTROL DIAPHRAGM VALVE

1. With engine coolant temperature below 97°-111°F (36-44°C), remove upper hose from purge control diaphragm valve and connect vacuum gauge to hose. Start engine and run at idle speed. Check that there is no vacuum. If there is vacuum, replace thermovalve and retest.
2. With engine coolant temperature above 97°-111°F (36°-44°C), remove upper hose from purge control diaphragm valve and connect vacuum gauge to hose. Start engine and run at idle speed. Check that there is vacuum.
3. If there is no vacuum, check thermovalve by pinching off hose between thermovalve and air cleaner. If there is vacuum, replace thermovalve. If there is no vacuum, check connecting vacuum hoses for leaks and obstructions.

Testing Charcoal Canister. Scheme 1

TWO-WAY VALVE

1. Remove gas cap and remove fuel vapor hose from fuel tank to the two-way valve. Connect vacuum/pressure pump with gauge to hose and slowly draw vacuum while observing gauge.
2. Vacuum should stabilize at.2-.6 in. Hg as two-way valve opens. Reverse pump and gauge connections and slowly pressurize vapor hose. Pressure should re is voltage, check control unit.
3. If there is no voltage at power valve control solenoid valve, remove hose from inlet side of check valve and check vacuum. If there is vacuum, test check valve operation. If check valve tests OK, replace power valve solenoid control valve and retest. If there is no vacuum, check connecting hoses for leaks and obstructions.
4. With vacuum gauge connected to hose removed from power valve, ground Red wire of control unit and check that vacuum drops to zero. If vacuum drops, system is OK. If vacuum does not drop, check voltage at power valve control solenoid in control box. (Scheme 2) Connect negative lead of voltmeter to ground and connect positive lead to Green/Blue wire at control box connector.
5. If there is no voltage, check control unit. If there is voltage, replace power valve control solenoid valve and retest.

Checking Power Valve Control Solenoid Valve Voltage (Accord). Scheme 2

AIR VENT CUT-OFF SOLENOID VALVE

1. With engine coolant temperature below 158°F (70°C), remove upper hose from air vent cut-off solenoid valve and connect vacuum pump to the solenoid valve. Turn ignition key on and draw 4-5 in. Hg. Vacuum should hold steady.
2. If no vacuum, check for voltage at solenoid valve. If no voltage, replace air vent cut-off solenoid valve. If there is voltage, check that there is voltage at control unit connector Blue wire and Black/Yellow wire with ignition key on. Inspect thermosensor, vacuum switch A, and check control unit ground continuity (Brown/Black wire).
3. Start engine. After 5-6 seconds, vacuum should drop to zero. If not, check for voltage to solenoid valve. If there is voltage, replace air vent cut-off solenoid valve. If no voltage, check that there is voltage at control unit connector Blue wire and Black/Yellow wire with ignition key on. Inspect thermosensor, vacuum switch A, and check control unit ground continuity (Brown/Black wire).

INNER VENT SOLENOID VALVE

1. Remove air cleaner and filter element. Disconnect 3 hoses at inner vent solenoid valve and plug 2 ports. Connect a vacuum pump to other port. (Scheme 3) Turn ignition key on and draw 10 in. Hg. Vacuum should hold steady.
2. If no vacuum, check for voltage at inner vent solenoid valve. If no voltage, replace inner vent solenoid valve. If there is voltage, check that there is voltage at control unit connector Blue wire and Black/Yellow wire with ignition key on. Check control unit ground continuity (Brown/Black wire).
3. Start engine. Vacuum should drop to zero. If not, check for voltage to solenoid. If there is voltage, replace inner vent solenoid valve. If no voltage, check that there is voltage at control unit connector Blue wire and Black/Yellow wire with ignition key on. Check control unit ground continuity (Brown/Black wire).

Checking Inner Vent Solenoid Valve. Scheme 3

THERMOSENSOR

1. With engine coolant temperature below 104°F (40°C), remove connector from control unit. Using an ohmmeter, measure resistance between Blue/Yellow and Brown/Black wire terminals. Resistance should be above 1000 ohms.
2. Run engine until warm and check that cooling fan runs at least once. Measure resistance again. Resistance should be approximately 200 ohms. If thermosensor resistance is out of given range, replace thermosensor and retest.
3. If resistance is infinite, check wires to thermosensor for opens. Repair wiring and retest.

VACUUM SWITCH A

1. Remove connector from control unit and remove vacuum hose from vacuum switch A. Using an ohmmeter, measure continuity between Black/Yellow and Brown/White wire terminals on connector. There should be continuity.
2. Connect vacuum pump and gauge to vacuum port on vacuum switch A. Slowly draw vacuum and watch ohmmeter scale. When vacuum increases above 3.9 in. Hg, switch opens and ohmmeter should show no continuity (infinite resistance). Replace vacuum switch A if it does not operate as outlined.