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Functional Test

  1. Set parking brake. Shift automatic transmission to Park or manual transmission to Neutral. Start engine and attain normal operating temperature. Ensure A/C is off (if equipped).
  2. Turn engine off. On 4.2L, disconnect 3-wire connector from 4 in. and 10 in. Hg vacuum switch assemblies.
  3. On all engines, disconnect and plug vacuum hose connected to distributor vacuum advance mechanism. Connect timing light at No. 1 spark plug. Connect tachometer to coil negative terminal.
  4. Start engine and slowly increase RPM while observing timing mark and index with timing light. The ignition timing should advance smoothly as RPM increases. See Figure .
  5. If timing advances unevenly, check and repair centrifugal advance mechanism.
  6. Connect distributor vacuum advance hose and vacuum switch assembly 3-wire connector. Remove timing light and tachometer.
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