M/T Vehicles

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).
If vacuum is present, check for voltage at anti-afterburn control solenoid valve Yellow/Black wire. If there is no voltage present, check speed sensor. See SPEED SENSOR .
If voltage is present, disconnect vacuum hose No. 31 from anti-afterburn valve. Check for vacuum. If there is no vacuum present, locate restriction or blockage and retest.
If there are no defects found, replace anti-afterburn valve and retest. If vacuum is present, replace anti-afterburn valve and retest.

Fig 1: Testing Anti-Afterburn Valve Use finger to check for vacuum.
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.
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 SPEED SENSOR .
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.
If there is no vacuum, disconnect vacuum hose No. 30 from anti-afterburn control valve. If there is no vacuum present, check for leaks or disconnected hose and retest. If there is vacuum present, replace anti-afterburn valve and retest.