Toyota Corolla 1970-1987 Repair Guide

Spark Delay Valve

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Starting 1975, non-California models have a spark delay valve (SDV) in the distributor vacuum line. The valve has a small orifice in it, which slows down the vacuum flow to the vacuum advance unit on the distributor. By delaying the vacuum to the distributor, a reduction in HC and CO emissions is possible.

When the coolant temperature is below 95°F, a coolant temperature operated vacuum control valve is opened, allowing the distributor to receive undelayed, ported vacuum through a separate vacuum line. Above 95°F, this line is blocked and all ported vacuum must go through the spark delay valve.

TESTING



  1. Allow the engine to cool, so that the coolant temperature is below 95°F.
  2.  
  3. Disconnect the vacuum line which runs from the coolant temperature operated vacuum valve to the vacuum advance unit at the advance unit end. Connect a vacuum gauge to this line.
  4.  
  5. Start the engine. Increase the engine speed; the gauge should indicate a vacuum.
  6.  
  7. Allow the engine to warm-up to normal operating temperature. Increase the engine speed; this time the vacuum gauge should read zero.
  8.  
  9. Replace the coolant temperature operated vacuum valve, if it fails either of these tests. Disconnect the vacuum gauge and reconnect the vacuum lines.
  10.  
  11. Remove the spark delay valve from the vacuum lines, noting which side faces the distributor.
  12.  
  13. Connect a hand operated vacuum pump which has a built-in vacuum gauge to the carburetor side of the spark delay valve.
  14.  
  15. Connect a vacuum gauge to the distributor side of the valve.
  16.  
  17. Operate the hand pump to create a vacuum. The vacuum gauge on the distributor side should show a hesitation before registering.
  18.  
  19. The gauge reading on the pump side should drop slightly, taking several seconds for it to balance with the reading on the other gauge.
  20.  
  21. If Steps 9 and 10 are negative, replace the spark delay valve.
  22.  
  23. Remove the vacuum gauge from the distributor side of the valve. Cover the distributor side of the valve with your finger and operate the pump to create a vacuum of 15 in.Hg.
  24.  
  25. The reading on the pump gauge should remain steady. If the gauge reading drops, replace the valve.
  26.  
  27. Remove your finger; the reading of the gauge should drop slowly. If the reading goes to zero rapidly, replace the valve.
  28.  

 
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