Throughout the 1970s, emission standards for cars became progressively tougher. As engineers gained experience, they discovered that very precise control of ignition timing could have a major effect on both NOx and HC emissions. The result, ultimately, was a move to electronic spark mapping. But during the transition period of the late 1970s, a variety of vacuum controls were added to the advance/retard mechanism of the distributor. GM used what seems like hundreds of variations of thermal vacuum switches, vacuum delay valves, and such. This article, the final part of a series on GM emissions, reviews these GM vacuum spark control devices. Included in the discussion are timing tricks, thermal vacuum valves, vacuum reducer valves, spark advance vacuum modulators, and distributor vacuum delay valves.

  • Corporate Authors:

    Hearst Books

    Motor Books Department, 224 West 57th Street
    New York, NY  United States  10019
  • Publication Date: 1983-10

Media Info

  • Features: Photos;
  • Pagination: p. 37-39
  • Serial:
    • Motor
    • Volume: 160
    • Issue Number: 4

Subject/Index Terms

Filing Info

  • Accession Number: 00389416
  • Record Type: Publication
  • Source Agency: National Highway Traffic Safety Administration
  • Report/Paper Numbers: HS-036 672
  • Files: HSL, USDOT
  • Created Date: Oct 30 1984 12:00AM