GM Metro/Sprint 1985-1993 Repair Guide

Pulse Air Control System

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This system serves to reduce Hydrocarbon (HC), and Carbon Monoxide (CO) emission by supplying secondary air into the exhaust manifold when the engine coolant temperature is low or during deceleration. The thermal switch mounted in the intake operates according to the engine coolant temperature. This switch is connected to the ECM and the ECM to the Three Way Solenoid Valve (TWSV). When the TWSV receives an electrical signal from the ECM, it opens its inner valve to transmit vacuum from the intake manifold to the secondary air valve.

When the engine coolant temperature is low, the thermal switch is ON . Then the TWSV receives a signal from the ECM, and opens the valve. Thus the TWSV transmits vacuum to the secondary air valve to opens its valve.

In the secondary air valve, there is a reed valve. When the exhaust gas pressure is low, the reed valve opens and lets the air flow from the air cleaner into the exhaust manifold, when the secondary air valve opens. When the exhaust gas pressure is high, the reed valve closes by the high exhaust gas pressure and prevents backflow of the exhaust gas. Thus, the pulsating secondary air is supplied to the exhaust manifold.

When the coolant temperature is normal, the thermal switch is OFF , this system does not operate. During deceleration, the ECM sends an electrical signal to the TWSV to operate the secondary air valve, even though the thermal switch is OFF . Thus the Hydrocarbon (HC), and Carbon Monoxide (CO) emission can be reduced even during deceleration.

INSPECTION



System Operation

See Figures 1 and 2



Click image to see an enlarged view

Fig. Fig. 1: Checking the three way solenoid valve



Click image to see an enlarged view

Fig. Fig. 2: Checking the secondary air valve

Check hoses and pipe for cracks, kinks, damage or loose connections. Also, check lead wire of Three Way Solenoid Valve (TWSV) for loose connections. If above checks are satisfactory, then check system for operation according to the following procedures:

  1. Disconnect secondary air hose from air cleaner when engine is cold.
  2.  
  3. Start cold engine and run it at idle. In this state, check to be sure that air is drawn into hose (bubbling sound is heard from inside of hose).
  4.  
  5. Warm up engine to normal operating temperature.
  6.  
  7. With engine warm, make sure air is not drawn into hose during idling (no bubbling sound is heard). Depress accelerator pedal until engine revolution increases to over 3000 rpm and release pedal quickly. Air is drawn into hose during deceleration (bubbling sound is heard).
  8.  
  9. Disconnect coupler of thermal switch and connect terminals on wire harness side with lead wire to short. In this state, make sure air is drawn into hose during idling (bubbling sound is heard).
  10.  
  11. After checking, connect air hose to air cleaner and coupler of thermal switch.
  12.  

Three Way Solenoid Valve (TWSV)
  1. Label and disconnect 2 vacuum hoses from TWSV.
  2.  
  3. Blow into nozzle 1. Air should come out of 3 and not out of 2.
  4.  
  5. Disconnect coupler and connect 12 volt source to TWSV terminals. In this state, blow into nozzle 1. Air should come out of nozzle 2.
  6.  
  7. After checking, connect 2 vacuum hoses to TWSV.
  8.  

Secondary Air Valve
  1. Remove the secondary air valve with air pipe.
  2.  
  3. While applying vacuum to diaphragm of secondary air valve, blow into air hose. Air should come out of air pipe. Blow into air pipe. No air should come out of air hose.
  4.  
  5. Reinstall secondary air valve with air pipe.
  6.  

REMOVAL & INSTALLATION



Three Way Solenoid Valve (TWSV)
  1. Label and disconnect the solenoid valve vacuum hoses.
  2.  
  3. Disconnect the solenoid valve electrical connector.
  4.  
  5. Remove the attaching screws, then remove the solenoid valve.
  6.  
  7. Installation is the reverse of removal.
  8.  

Secondary Air Valve
  1. Disconnect the vacuum hose.
  2.  
  3. Disconnect the air hose.
  4.  
  5. Disconnect the air pipe.
  6.  
  7. Remove the secondary air valve.
  8.  
  9. Installation is the reverse of removal.
  10.  

 
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