Air Jet Control System Honda Prelude II

DESCRIPTION & OPERATION

To maintain optimum air-fuel ratio, main air jet control system controls air flow into main jets of the carburetor throats. When vehicle is being started, or running in power mode, control unit energizes main air jet solenoid valve in air cleaner to close extra air passage, increasing fuel flow.

COMPONENT TESTING

1. Ensure engine is at operating temperature. Remove air cleaner cover and filter element. Disconnect hose from main air jet solenoid valve and install vacuum pump to solenoid valve. Start engine and apply vacuum at idle. If no vacuum is present, proceed to step 4).
2. If there is vacuum, check for voltage at main air jet solenoid valve. If there is no voltage, replace solenoid valve and retest. If there is voltage, check the following
3. Check speed sensor (auto. trans. only), intake air temperature sensor and vacuum switch A. Check for voltage at control unit connector (Black/Yellow wire) with ignition on. There should be voltage. If no voltage, check wiring. Ensure Brown/Black wire between control unit and ground has continuity.
4. Disconnect vacuum hose No. 2 from control box No. 1. Apply vacuum with engine at idle. If vacuum remains steady, disconnect vacuum gauge and reconnect air hoses and air cleaner. If there is no vacuum, check for voltage at main air jet solenoid valve.
5. If there is voltage, replace the solenoid valve and retest. If there is no voltage, check the following: speed sensor (auto. trans. only), intake air temperature sensor and vacuum switch A. Check for voltage at control unit connector (Black/Yellow wire) with ignition on.
6. There should be voltage. If no voltage, check wiring. Ensure Brown/Black wire between control unit and ground has continuity.

A/T Models

1. Raise and support front of vehicle. Set parking brake and block rear wheels. Push voltmeter or test light positive probe into Yellow/Black wire terminal at control unit connector.
2. Connect negative probe to ground. Start engine. Place vehicle in 2nd position (gear selector in "2" position) and accelerate slowly. Battery voltage should be as shown in SPEED SENSOR VOLTAGE CHECK table. SPEED SENSOR VOLTAGE CHECK Speed Voltage Below 11 MPH Yes Above 16 MPH No
3. If voltmeter readings do not correspond to above MPH ranges, install a new speed sensor and retest. If there was no voltage during step 2), check for bad electrical connection, fuse or faulty speed sensor. Replace or repair as necessary and retest.

INTAKE AIR TEMPERATURE SENSOR

Disconnect air intake temperature sensor connector. Check for continuity between sensor terminals when air temperature is below 40°F (4.5°C). Check for no continuity when air temperature is above 73°F (23°C). Replace sensor if not within specifications.

VACUUM SWITCH A

1. Disconnect vacuum hose No. 2 to control box at vacuum hose manifold. Connect a hand vacuum pump to hose. Check for continuity between Black/Yellow and Brown/White terminals of control box connector.
2. Apply over 4 in. Hg vacuum. Continuity should not be present. If present, replace vacuum switch A. Release vacuum. There should be continuity. If not, replace vacuum switch A.

CONTROL UNIT CONNECTOR

Check for voltage at control unit connector (Black/Yellow wire) with ignition on. There should be voltage. If there is no voltage, check wiring. Check Brown/Black wire for continuity between control unit and ground. There should be continuity.