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Tachometer Inaccurate

  1. Disconnect ignition coil connector (gasoline) or generator connector (diesel). Connect a hand-held tachometer to ignition coil (gasoline) or generator (diesel) tachometer output (White wire). Start and operate engine at 1000 RPM without racing engine. Record IPC tachometer. Record RPM on hand-held tachometer.
  2. If RPM indicated by hand-held tachometer is within 250 RPM of vehicle tachometer, tachometer accuracy is acceptable. If RPM indicated by hand-held tachometer is not within 250 RPM of vehicle tachometer, and no other driveability or emission problems are present, replace instrument cluster.
NOTE: Before performing following test, ensure Distributor Ignition (DI) system is operating correctly. See appropriate BASIC DIAGNOSTIC PROCEDURES article in ENGINE PERFORMANCE.
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