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.
In addition, Accord models use a liquid/vapor separator pipe, air vent cut-off diaphragm, vacuum holding solenoid valve, carburetor fuel cut-off solenoid valve, power valve control solenoid, and a control unit.
Civic models use an air vent cut-off diaphragm, vacuum holding solenoid valve, and carburetor fuel cut-off solenoid valve. The Civic Coupe also has a fuel cut valve.
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 valve closes float bowl vent to secondary bore and opens vapor vent to canister. When engine is running, manifold vacuum opens air vent cut-off valve to secondary bore and closes off vent to canister. Vacuum holding solenoid stabilizes vacuum on air vent cut-off diaphragm.
When engine is not running on Prelude, 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.
When engine is not running, fuel cut-off solenoid valve shuts off main and slow primary fuel metering passages to carburetor bore. On Accord, when ignition key is off, power valve fuel passage to carburetor bore is closed by power valve control solenoid and check valve.
MAINTENANCE
Inspect system, hoses, and connections. Test all components every 60,000 miles or every 5 years.
THERMOVALVE & PURGE CONTROL DIAPHRAGM VALVE
- 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.
- 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.
- 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 (Civic)
- Remove gas cap and remove 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.
- 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.
- 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.
- 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.
- If there is no voltage, check control unit. If there is voltage, replace power valve control solenoid valve and retest.
Two-Way Valve (Accord)
- Remove fuel filler cap. Remove vapor line from liquid/vapor separator pipe and connect to T-Fitting from vacuum gauge and vacuum pump.
- Slowly draw vacuum while watching gauge. Vacuum should stabilize at 0.2 to 0.6 in.Hg (5 to 15 mmHg). If vacuum stabilizes momentarily (two-way valve opens) between 0.2 to 0.6 in.Hg (5 to 15 mmHg) go to step 3. If vacuum stabilizes (valve opens) below 0.2 in.Hg (5 mmHg) or above 0.6 in.Hg (15 mmHg) install new valve and re-test.
- Move hand pump hose from vacuum to pressure fitting, and move vacuum gauge hose from vacuum to pressure side.
- Slowly pressurize vapor line while watching gauge. Pressure should stabilize at 1 to 2.2 in.Hg (25 to 55 mmHg). If pressure momentarily stabilizes (valve opens) at 1 to 2.2 in.Hg (25 to 55 mmHg), the valve is OK. If pressure stabilizes below 1 in.Hg (25 mmHg) or above 2.2 in.Hg (55 mmHg), install new valve and re-test.
Checking Power Valve Control Solenoid Valve Voltage (Accord). Scheme 2
AIR VENT CUT-OFF DIAPHRAGM
- Remove air vent cut-off diaphragm hose from carburetor. Connect vacuum pump to hose and try to draw vacuum. There should be no vacuum. Turn ignition key on and draw vacuum. Vacuum should hold steady.
- If no vacuum can be drawn with key on, check for leaks in hose connections. If hoses are OK, check for voltage at vacuum holding solenoid valve. If there is voltage, replace vacuum holding solenoid valve and retest.
- Start engine and run at idle. There should be vacuum. If not, check for blockage in hose. If no blockage, replace vacuum holding solenoid valve and retest.
- Turn ignition key off. Vacuum should drop to zero. Disconnect vacuum pump from vacuum holding valve hose and connect to air vent cut-off diaphragm. Draw a vacuum. Vacuum should remain steady. If vacuum decreases, replace diaphragm and retest. Remove vacuum pump and replace hose.