Anti-Afterburn System Honda Civic III

DESCRIPTION

The anti-afterburn system supplies fresh air to intake manifold when manifold vacuum suddenly increases, as during sudden deceleration. This leans the air/fuel mixture and helps maintain proper mixture for complete combustion.

OPERATION

The anti-afterburn valve is sensitive only to sudden increases in vacuum. The length of time it stays open is controlled by a diaphragm that senses change in manifold vacuum.

When manifold vacuum suddenly increases, as during sudden deceleration, diaphragm/valve unit is pulled downward. Air flow from air chamber to sensing chamber is restricted by an orifice, creating a pressure differential on diaphragm, which holds valve open.

This unbalanced condition lasts for a few seconds until pressure in both chambers is equalized by air entering through orifice. When both chambers are equalized, spring pressure pushes diaphragm up, closing valve.

Scheme 10

1. On High Altitude 1300/1500 HF and Federal/High Altitude 1500 manual transmission except HF models, disconnect both No. 26 vacuum hoses from vacuum control valve and connect them together. Disconnect air suction hose at air valve. (Scheme 10)
2. If no vacuum is present, proceed to step 4). If vacuum is present at air valve, disconnect hose No. 26 at air valve and check for vacuum at hose No. 26. (Scheme 10): Checking Air Valve Feel for vacuum.
3. If vacuum is present, replace control switch and retest. If no vacuum is present, replace air valve and retest.
4. Start engine and quickly raise engine speed to 3500 RPM. Close throttle suddenly. If there is vacuum, test is complete for 1500 except HF or, proceed to «AIR CONTROL SOLENOID VALVE»(/honda/civic/iii-1983-1987/remont/testing-diagnostics/#anti-afterburn-system) test on 1300/1500 HF.
5. If no vacuum is present, disconnect vacuum hose No. 26 from air valve. Check for vacuum at hose No. 26 during deceleration above 3500 RPM.
6. If vacuum is present, replace air valve and retest. If no vacuum is present, check vacuum line to intake manifold for leaks or blockage. If okay, replace control switch and retest.

Scheme 11

1. Remove cover to control box No. 1. Disconnect hose to air filter at air control solenoid valve and connect a vacuum gauge to solenoid valve. (Scheme 11): Checking Air Control Solenoid Valve
2. If no vacuum is present, proceed to step 5). If vacuum is present, check for voltage at air control solenoid valve Blue/Red wire. If there is voltage, check vacuum switch A. Check for voltage at control unit connector (Blue wire) with ignition switch on.
3. There should be voltage. If there is no voltage, check Blue wire between ignition coil and control unit. If there is no voltage, replace air control solenoid valve and retest. Check for voltage at control unit connector (Black/Yellow wire) with ignition switch on.
4. There should be voltage. If no voltage, check wiring and fuse. Check Black wire (Brown/Black wire on 1500 except HF) for continuity between control unit and ground. There should be continuity.
5. Disconnect vacuum hose No. 4 at control box No. 1. Raise engine speed to more than 1400 RPM and check for vacuum. If vacuum is present, system is okay. If no vacuum is present, check for voltage at air control solenoid Blue/Red wire.
6. If voltage is present, replace air control solenoid valve. If no voltage is present, check vacuum switch A. Check for voltage at control unit connector (Blue wire) with ignition switch on. There should be voltage.
7. If there is no voltage, check Blue wire between ignition coil and control unit. If there is no voltage, replace air control solenoid valve and retest. Check for voltage at control unit connector (Black/Yellow wire) with ignition switch on.
8. There should be voltage. If no voltage, check wiring and fuse. Check Black wire (Brown/Black wire on 1500 except HF) for continuity between control unit and ground. There should be continuity.

Scheme 12

1. Disconnect air suction lower hose from the anti-afterburn valve. Start engine. Raise engine speed to 3500 RPM and close the throttle suddenly. Check for vacuum at air suction lower hose. If there is no vacuum, proceed to step 5).
2. If vacuum is present, check for voltage at anti-afterburn control solenoid valve Yellow/Black wire. If no voltage is present, check speed sensor. See «COMPONENT TESTING»(/honda/civic/iii-1983-1987/remont/testing-diagnostics/#anti-afterburn-system).
3. If voltage is present, disconnect vacuum hose No. 31 from anti-afterburn valve. Check for vacuum. If no vacuum is present, locate restriction or blockage and retest.
4. If no defects are found, replace anti-afterburn valve and retest. If vacuum is present, replace anti-afterburn valve and retest. (Scheme 12): Testing Anti-Afterburn Valve Use finger to check for vacuum.
5. Raise front of vehicle and support with safety stands. Block rear wheels and set parking brake. Place shift or selector lever in second or "2" position and accelerate. Release throttle suddenly and check for vacuum during deceleration above 10 MPH.
6. If there is vacuum, system is okay. If there is no vacuum, check for voltage at anti-afterburn control solenoid valve above 10 MPH. If there is voltage, check speed sensor. See TROUBLE SHOOTING in this article.
7. If there is no voltage, disconnect vacuum hose No. 31 from anti-afterburn valve and check for vacuum above 10 MPH. If there is vacuum, replace anti-afterburn control valve and retest.
8. If there is no vacuum, disconnect vacuum hose No. 30 from anti-afterburn control valve. If no vacuum is present, check for leaks or disconnected hose and retest. If vacuum is present, replace anti-afterburn valve and retest.

Automatic Transmission

1. Disconnect air suction lower hose from anti-afterburn valve. Start engine and quickly raise engine speed to 3500 RPM and close throttle suddenly. Check for vacuum at air suction lower hose. There should be vacuum.
2. If there is vacuum, proceed to step 4). If there is no vacuum, check for voltage at anti-afterburn control solenoid valve Yellow/Black wire. If no voltage is present, check for voltage at control unit connector (Black/Yellow wire). If no voltage, check wiring.
3. Check Brown/Black wire for continuity between control unit and ground. There should be continuity. Check wiring and fuse between control unit connector (Blue/White wire) terminal and ignition switch start terminal.
4. If voltage is present, disconnect vacuum hose No. 31 from anti-afterburn valve. Check for vacuum. If no vacuum is present, disconnect vacuum hose No. 30 from anti-afterburn valve and check for vacuum. If there is no vacuum, check for leaks or blockage and retest.
5. If vacuum is present, replace anti-afterburn valve and retest. Stop engine. Connect voltmeter to anti-afterburn control solenoid valve. Turn ignition switch to start position and release key while checking voltage.
6. There should be no voltage for 4 seconds after releasing key. Voltage should return after 4 seconds. If voltmeter does not indicate as described, check for voltage at control unit connector (Black/Yellow wire). If no voltage, check wiring.
7. Check Brown/Black wire for continuity between control unit and ground. There should be continuity. Check wiring and fuse between control unit connector (Blue/White wire) terminal and ignition switch start terminal.

Cold Engine

1. Ensure engine coolant temperature is below 122°F (50°C) on 1300 models and 104°F (40°C) on 1500 models. Pinch vacuum hose No. 26 at control box No. 1. Disconnect vacuum hose No. 26 from air valve.
2. Start engine. Quickly raise engine speed to 3500 RPM and close throttle suddenly several times. Check for vacuum at hose No. 26. If no vacuum is present, proceed to HOT ENGINE test. If there is vacuum present, replace thermovalve D and retest.

Hot Engine

1. Warm engine to operating temperature. Raise engine to 3500 RPM and close throttle suddenly several times. Check for vacuum at air valve hose No. 26. If vacuum is present, system is okay.
2. If no vacuum is present, disconnect vacuum hoses No. 19 and 20 from control valve and check for vacuum. If vacuum is present at both hoses, replace vacuum control valve and retest. If no vacuum is present at hose No. 19, replace thermovalve D and retest.
3. If no vacuum is present at hose No. 20, check vacuum line to intake manifold for leaks or blockage. Repair or clean as necessary and retest.

CONTROL UNIT CONNECTOR

1. Check for voltage at control unit connector Blue wire with ignition on. There should be voltage. If there is no voltage, check wiring between control unit and ignition coil.
2. Check for voltage at Black/Yellow wire with ignition on. There should be voltage. If there is no voltage, check wiring. Check Black wire (1300 models) or Brown/Black wire (all other models) for continuity between control unit and ground. There should be continuity.

SPEED SENSOR

1. Raise and support front of vehicle. Push voltmeter or test light positive probe into Yellow/Black wire (Yellow wire on Accord) 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 6 MPH Yes Above 12 MPH No
3. If voltmeter readings do not correspond to appropriate MPH ranges, install a new speed sensor and retest. If there was no voltage during speed sensor test, check for bad electrical connection, fuse or faulty speed sensor. Replace or repair as necessary and retest.

VACUUM SWITCH A

1. Disconnect vacuum hose to vacuum switch A and connect a hand vacuum pump to hose. Apply vacuum to switch. Check for voltage at Black/Red wire (1300/1500 HF) or Black/Orange wire (1500 except HF) of vacuum switch A (Blue/Black wire on hatchback/sedan manual transmission with 1500 except HF).
2. Voltage should be available when vacuum below 2 in. Hg (1300/1500 HF) or below 1.2 in. Hg (1500 except HF) is applied. If there is no voltage, replace vacuum switch A and retest.

See also:
• AIR CONTROL SOLENOID VALVE