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Tachometer Inaccurate

WARNING: This page does not describe the selected car, but rather 11 other vehicles, including the 1999 GMC Yukon, 1999 GMC Suburban, 1999 GMC Pickup, 1999 GMC Cab & Chassis, and 1999 GMC C3500 HD. However, it is still accessible from the selected car via links, so may be relevant.
  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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