Nissan Z - ZX 1970-1988 Repair Guide

Deceleration Control System



See Figure 1

This system is used on 1981 and later (turbocharged) models and is designed to control the intake manifold vacuum under decelerating driving conditions so as to reduce oil consumption. Air is directed from a 3-way connector through an air hose and vacuum control valve. To keep oil consumption low, as the air enters, the intake manifold vacuum will be maintained at less than the specified level. To check the operation of the vacuum control valve proceed as follows:

  1. Disconnect one end (Air Regulator side) of the air hose connecting the 3-way connector to the control valve.

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Fig. Fig. 1: Checking the vacuum control valve

  1. Make sure that the vacuum control valve operates when the engine speed is decreased from 3,500-4,000 rpm to idle.
  3. Place a finger over the hose end to check for valve operation. If vacuum is not present, replace the vacuum control valve.

The above procedure is not accurate at altitudes above 2,300-4,000 ft. (701-1,219 meters).