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Test SK: Tachometer Always Indicates Too High Or Too Low; No Tachometer Signal; Signal Erratic

  1. Check Electronic Instrument Cluster (EIC) Tachometer

    Ensure engine is operating properly and not misfiring. Connect Rotunda Digital Dwell-Tach-Volts Analyzer or equivalent to ignition coil. Start and run engine at 2500 RPM. If vehicle tachometer and service tachometer read within 300 RPM, go to step  3 . If tachometer readings differ by more than 300 RPM, go to next step.

  2. Check EIC Ground Circuit

    Remove Electronic Instrument Cluster (EIC). To remove EIC, see ELECTRONIC INSTRUMENT CLUSTER  under REMOVAL & INSTALLATION. Using DVOM, measure resistance between ground and EIC connector "B" terminals No. 8 (Black/White wire), No. 2 (Black wire) and EIC connector "A" terminal No. 6 (Black wire). All circuits should be grounded and have less than 5 ohms resistance. See Figure . If any reading is 5 ohms or more, repair open or poor connection in affected ground as necessary. See WIRING DIAGRAMS  .

  3. Check Wiring For No Tach Signal Or For Erratic Signals

    Remove EIC. See ELECTRONIC INSTRUMENT CLUSTER  under REMOVAL & INSTALLATION. Unplug EIC connector "B". Connect Rotunda Digital Dwell-Tach-Volts Analyzer or equivalent between ground and EIC connector "B" terminal No. 20 (Dark Green/Yellow wire). Start engine. While monitoring tachometer value, wiggle connections and related wiring to check for intermittent condition. If any intermittent condition is detected, repair as necessary.
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