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Anti-Afterburn System Honda Accord III

Testing & Diagnostics 1 illustration ~879 words

DESCRIPTION

The anti-afterburn system supplies fresh air to intake manifold when manifold vacuum suddenly increases, as when throttle is suddenly decelerated. This leans the air/fuel mixture and helps maintain proper mixture for complete engine 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. Vacuum 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.

Fig. 1: Anti-Afterburn System Diagram
Scheme 1: Anti-Afterburn System Diagram

Cold Engine

Note. Engine coolant temperature must be below 158°F (70°C).

  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. If there is no vacuum, proceed to step 5).
  2. If there is vacuum, check for voltage at anti-afterburn control solenoid valve (Green/White wire). If there is no voltage, check for continuity between speed sensor wire terminals and thermosensor wire sensor wire terminals.
  3. If there is no continuity, replace thermosensor and retest. If there still is no continuity, replace speedometer/speed sensor. If there is voltage, disconnect upper vacuum hose at anti-afterburn valve.
  4. Check for vacuum. If there is no vacuum, check for leaks or disconnected hose. If hose is okay, replace anti-afterburn control solenoid valve and retest. If there is vacuum, replace anti-afterburn valve and retest.
  5. Raise front of vehicle and support with jack stands. Set parking brake and block rear wheels. Place shifter in 2nd or "2" position and accelerate. Quickly release throttle and check for vacuum during deceleration at speeds more than 15 MPH. There should be vacuum.
  6. If there is vacuum, proceed to HOT ENGINE test. If there is no vacuum, check for voltage at anti-afterburn control solenoid valve at speeds more than 15 MPH. If there is voltage, replace speed sensor. If there is no voltage, disconnect upper vacuum hose at anti-afterburn valve and check for vacuum at speeds more than 15 MPH.
  7. If there is vacuum, replace anti-afterburn control valve and retest. If there is no vacuum, disconnect vacuum hose No. 20 from anti-afterburn valve and check for vacuum. If there is no vacuum, check for leaks or disconnected hose and retest. If there is vacuum, replace anti-afterburn valve and retest.

Hot Engine

  1. Disconnect air suction lower hose at anti-afterburn valve. Start engine. Raise engine speed to 3500 RPM and quickly release. If there is vacuum at hose, test is complete.
  2. If there is no vacuum, check for voltage at anti-afterburn control solenoid valve (Green/White wire). If there is voltage, replace thermosensor and retest. If there is no voltage, replace anti-afterburn control solenoid valve 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 Brown/Black wire 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 wire on terminal at control unit connector.
  2. Connect negative probe to ground. Start engine. Place vehicle 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 10 MPH Yes Above 20 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.

THERMOSENSOR

Remove leads from thermosensor. Check for continuity. There should be continuity when engine coolant temperature is above 158°F (70°C) and no continuity when coolant temperature is below 158°F (70°C).

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 Green/Yellow and Black terminals. Turn ignition on and check voltage.
  2. Voltage should be available when vacuum below 3.1 in. Hg is applied. If there is no voltage, replace vacuum switch A and retest.

VACUUM SWITCH B

  1. Disconnect vacuum hose to vacuum switch B and connect a hand vacuum pump to hose. Apply vacuum to switch. Check for voltage at Yellow/Blue and Black terminals. Turn ignition on and check voltage.
  2. Voltage should be available when vacuum below 1.2 in. Hg is applied. If there is no voltage, replace vacuum switch B and retest.

VACUUM SWITCH C

  1. Disconnect vacuum hose to vacuum switch C and connect a hand vacuum pump to hose. Apply vacuum to switch. Check for voltage at Yellow/Red and Black terminals. Turn ignition on and check voltage.
  2. Voltage should be available when vacuum below 2.4 in. Hg is applied. If there is no voltage, replace vacuum switch C and retest.

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