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Home › Nissan-Datsun › 1972 › 521 Pickup Automatic Trans › Repair and Diagnosis › Engine Performance › Engine Control Systems › 1972 510 & Pickup Engine Modification › Testing › Accelerator Switch (521 Only) › Boost Controlled Deceleration Device

Boost Controlled Deceleration Device

  1. With engine at normal operating temperature, connect vacuum gauge to intake manifold and connect tachometer to measure engine speed. Increase engine speed to 3000-3500 RPM and then quickly release throttle. At this moment, manifold vacuum should read above 23.6 in. Hg and gradually fall to about 19.7 in. Hg at idle. This change in vacuum should take about 4 or 5 seconds and engine speed should drop to about 1000 RPM.
  2. If device is set to actuate at vacuum which is higher than the desired level, the delay in returning to idle will be less than the specified 4 or 5 seconds. If device is set to actuate at vacuum which is lower than the desired level, the delay will be more than the specified 4 or 5 seconds.
  3. To set the device to operate at the correct vacuum (21.85-22.44 in. Hg on manual trans., or 21.06-21.65 in. Hg on auto, trans.), turn adjusting screw so that the delay in returning to 1000 RPM from 3000-3500 RPM is about 4 or 5 seconds.
    NOTE: Turning adjusting screw 1/8 turn in either direction will cause a change of 0.79 in. Hg of vacuum needed to operate device. Turn screw clockwise to decrease vacuum required (increasing delay) or counterclockwise to increase vacuum required (decreasing delay).
    Fig 1: Adjusting Operating Pressure
    G09355031Courtesy of NISSAN NORTH AMERICA, INC.
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