Power Valve: Testing and Inspection

Fig. 20 Connecting hand pump gauge to power valve.:

The power valve supplies supplementary fuel into the primary main fuel passage when the vehicle is operated in the power mode. In normal driving modes other than acceleration, manifold vacuum is applied on the diaphragm of the power valve, keeping the valve closed. When throttle valve is suddenly opened to accelerate the power valve opens because of decreased manifold vacuum, and additional fuel is supplied to the primary main fuel passage through power jet.
When ambient temperature is below the set temperature of the intake air temperature sensor, power valve control solenoid valve is operated by control unit which receives the signal from intake air temperature sensor. Manifold vacuum leaks through the solenoid valve so that the power valve remains open regardless of throttle valve position.
Test power valve as follows:
1. Disconnect hose from power valve, connect suitable hand vacuum pump to valve and apply vacuum to valve, Fig. 20.
2. Vacuum should remain steady. If it does, proceed to step 3. If vacuum decreases, replace diaphragm.
3. Start engine and allow to reach normal operating temperature, then disconnect hose from power valve and connect suitable vacuum gauge to hose. With engine running, vacuum should be present. If vacuum is present, proceed to step 6. If vacuum is not present, check for voltage at lock solenoid in the emission control box.
4. If voltage is not present, check wiring and fuse. If voltage is present, check vacuum between power valve control solenoid valve and lock solenoid valve.
5. If vacuum is present, replace lock solenoid and retest, If vacuum is not present, check voltage at the power valve control solenoid valve. If voltage is present, replace power valve control solenoid valve. If voltage is not present, check the following:
a. Speed sensor.
b. Thermosensor.
c. Intake temperature sensor.
d. Vacuum switch A and C.
e. Check voltage at control unit connector black/yellow wire with ignition switch on. Voltage should be present. If voltage is not present, check wiring.
f. Check voltage at control unit connector blue wire with ignition switch on. Voltage should be present. If voltage is not present, check blue wire between ignition coil and control unit.
g. Check brown/black wire for continuity between control unit and ground. Continuity should be present.
6. Turn ignition switch off. Vacuum should remain steady. If vacuum remains steady, proceed to step 7. If vacuum does not remain steady, replace lock solenoid valve.
7. Remove No. 1 control box cover and pinch hose connected to vacuum switch A. Disconnect upper tube from lock solenoid valve and connect it to a suitable vacuum pump. Check for vacuum with engine speed at 3000 RPM.
8. If vacuum is not present, test is complete. If vacuum is present, check voltage at power valve control solenoid valve.
9. If voltage is not present, replace power valve control solenoid valve. If voltage is present, repeat step 5a through 5g.