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Engine tach is way off-gctid823400

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    Engine tach is way off-gctid823400

    I have a 2007 Discovery with the 5.7 MAG fuel injected engine and a B3. The dash tach is as much as 1,000 RPM off at cruise of 3,500 from the Smartcraft which I assume to be correct. I had the tach rebuilt by Faria and no help. The rest of the gauges seem OK. Does the dash tach use the same pick up as the Smartcraft? If not, where does the dash tach get its signal from? I hate to have my Smartcraft stuck on the tach mode when it has so much information to offer. Any suggestins?

    Thanks!

    #2
    Many tachs have the wires going to the tach are connected with a molded connector that clips on to the threaded studs. Corrosion builds up inside the connector and sometimes the wires break internally. I've been able to fix tach issues by cutting off the molded connectors and using crimp-on ring terminals on the wires. I use brass nuts and washers to attach the ring terminals to the threaded posts. This may work in your case.
    1999 3788, Cummins 270 "Freedom"
    2013 Boston Whaler 130 SS
    Anacortes, WA

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      #3
      Norton Riders suggestions are very good, but is this a new issue or always been there?

      If not new, have a read of http://www.hot-spark.com/tachometer-fix.pdf. I had to install a diode for the coil of a car I just restored as the tach was indicating too high RPM.

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        #4
        I have Faria tachs at upper and lower helm stations on my 288. Upper tach is consistently 200 rpm higher than gauge at lower helm. Checked on engine analyzer and lower tach is correct...... I just live with 200 rpm error and mentally adjust!
        2007 288 Discovery Command Bridge
        Tacoma, WA

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          #5
          I cut off the three wire molded cap and reattached each wire with a ring terminal to the tach. No change. Still shows only about 2,600 RPM when I'm doing 3,500. Tach mirrors the Smartcaft up to about 1,000 RPM then falls way behind. Any other suggestions?

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