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Another erratic tach, '97 Johnson SPL

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  • Another erratic tach, '97 Johnson SPL

    I am trying to get a tach working on a new to me J90TSLEU. It has an unregulated charging system. I took a tach I had from a '89 Evinrude 40 hp and tried to use it. It had been acting erratically on the 40, usually reading way high randomly, then going back to normal. It did pretty much the same thing on the 90 so I figured it was bad. I bought a new Teleflex Amega model 58255P. The application chart says it will work with "Evinrude / Johnson, All V Models" At the bottom of the chart it says "Johnson / Evinrude 88 - 112 SPL models may require the addition of a 2000 ohm resistor or a BRP regulator." The installation instructions do not mention this resistor or where to install it. I called Teleflex tech support, and was told to place it inline with the signal wire, then the tech called me back and said he made a mistake and to put it inline with the ignition (purple) wire. I did this and the tach did not work at all, not even go to zero when swithced on. The voltage after the resistor was about 2.8. I removed the resistor and the tach seemed to work OK on muffs at idle and high idle. On the water, idle and at no wake speed it seemed OK. When I opened it up, tach climbed up and at what I guess was 4000 - 4500 rpm it dropped down to read 1200 or so, when I backed down to cruise speed, guessing 3500 - 4000 rpm, the tach climbed up to full scale, 7000. It did this several times. I reinstalled the resistor in the ign. wire and the tach does not work at all.

    Searched other erratic tach posts here and they usually point to rectifier problems. My rectifier checks out good with ohmmeter test per service manual. I did not try to heat the rectifier to see if results change. All connections and wiring are good.

    Does anyone know where to connect the 2k ohm resistor, if in fact it is required? The tach instructions say it "may" be required. Or do I need a regulator? If so, do I replace my rectifier with the BRP rectifier/regulator from the higher output stators, or is a seperate regulator available as an add-on?

    Any other tricks to install tach on SPL engines before I call Teleflex again?

    Oh, the selector on the tach is set to 6 per service manual and tach instructions.

    I'm trying to figure out what prop pitch I need for this boat/ engine, plus I just like having a tach I can trust.

    Thanks guys.

  • #2
    Re: Another erratic tach, '97 Johnson SPL

    The resistor is suppose to be installed between the send terminal (gray wire) and gound. Seems like Teleflex should know that.
    "A manual is a cheap investment"
    Fair Winds and Following Seas
    PTC USN ret


    • #3
      Re: Another erratic tach, '97 Johnson SPL

      Thanks, bhile. I'll do that tonight. Unfortunately, can't on-water test til the weekend. I'll reply with results.


      • #4
        Re: Another erratic tach, '97 Johnson SPL

        I have the same results with the resistor installed between the signal and ground posts. Seems OK up to about 3500, then goes crazy, full scale, low reading, floating around, etc. What else should I check? Do I need a voltage regulator for accurate tach readings? Or a OMC/BRP tach designed specifically for these SPL motors? Maybe new tach is bad out of the box?

        Thanks for any suggestions.


        • #5
          Re: Another erratic tach, '97 Johnson SPL

          Ooops! Ignore my last post about same results with resistor between send and ground. I had it in line with send wire. I'll try again, results next weekend unless I can sneak away early from work during the week. BTW I saw an old post about an erratic tach which suggested the resistor between the ign and ground posts. Is this an either / or situation?


          • #6
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            Re: Another erratic tach, '97 Johnson SPL

            Thanks, bhile. The resistor between the send and ground terminals did the trick, tach is smooth and steady now. Teleflex should print this simple solution in the installation instructions!