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  • Fuel Gauge inacurrate

    2002 Mastercraft 197:
    I am about to search history again but did not find the advice I was looking for last time. Anyway fuel gauge reads wrong. It does read now. It used to say empty. Dealer replaced fuel gauge, now it reads but it is not accurate. I don't mean not perfectly calibrated. It is not reading correct. It originally always read full way too quickly (probably 3/4 tank or sooner) but it did track down to empty correctly. Now it can say 3/4 tank and be empty. I suspect the sending unit. It is a 3 pin sensor. I disconnected the lead coming to the sensor to measure the incoming signal. I did measure 12 volts supply in the plug. I got 7 volts from the middle pin to ground. I am assuming that is correct. If someone can tell me that probably indicates the sending unit, I 'll just buy one. If not any trouble shooting ideas are welcomed. I went to the automotive store to buy a connector where I could put the sensor in a glass of fuel and test output but they did not have a matching plug.

    One other note, I had a polarity issue (hooked battery up backwards while changing in the dark, I bought a battery and the caps were on the wrong terminals.) This was the cause of the fuel gauge being replaced along with a couple of others at the same time. Possibly there is something else that could have fried when that was done. But everything else electric works now including all other gauges, the speed control, blowers, pumps, dashlights, etc.

  • #2
    I did find a test method but I do need the correct electrical connector and apparently need some resistors to confirm the gauge . Anyone know if it is the same resistors for the 3 pin? I may can figure this out from the middle pin voltage. I will think more on this at a better time of day.

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    • #3
      is it the right length?
      sigpic...A bad day water skiing still beats a good day at work...1995 Pro Star 205....

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      • #4
        it may not be perfect, that could cause the full too soon issue, but it always worked accurately from 3/4 down to empty before. thats all I really care about.

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        • #5
          I'm having the same problem but mine only goes to about 1/8 of a tank and stays there.

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          • #6
            Testing the sending unit versus the gauge was going to be a pain. I ordered a sending unit. It fixed the problem. I have not filled it or driven to empty to check accuracy. But looking at the amount of gas in the tank, it seemd to read right. Andd after adding 5 gallons, it seemd to go up the appropriate amount.
            Therefore, short of a computer to check codes, my guess is that if you measure 12 v on supply and 7v middle pin when unplugging the connection to the sending unit. The problem is probably the sending unit.

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            • #7
              woodrow,
              Where did you order your new sending unit, I need one my self and I'm finding lots of 2 wire but having trouble finding what I think is the right 3 wire. My boat is an '01 Prostar btw.

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              • #8
                Man, mine's po-zessed as well this season. sometimes when i turn the key on it works fine, sometimes it registers incorrectly, sometimes doesn't work at all, and each time i turn it on a different result. put in a new sending unit last fall and it worked fine then. checked the wiring 4 times so far. at this point i just keep filling it up. problem solved!

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                • #9
                  I adjsuted mine last year using the calibration instructions...and it's worked great ever since.

                  http://www.centroidproducts.com/3wire.htm

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                  • #10
                    you can test the resistance to check accuracy...
                    sigpic...A bad day water skiing still beats a good day at work...1995 Pro Star 205....

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                    • #11
                      This 25 is my second Mastercraft, and both boats have had fuel gauge problems. The 2012 35 was always off by 1/2 to 1/4 of a tank and the gauge on the 2013 25 does not work at all. I know the sending unit on the new boat is probably bad or a wire on one of the plugs pulled out , but I don't want to take it to dealer until my 20 hour service. I had a hurricane deck boat that had both an electric gauge and a simple manual float gauge on top of the tank. How hard would it be to install a simple manual float gauge on this new boat so incase after I have the electrical gauge fixed it malfunctions again? I would mark the tank, but I cant see the fuel through the tank walls. Has anyone put a manual float gauge on their tanks? Does anybody have any ideas or suggestions?

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                      • #12
                        I could not find after about 30 minutes so I went to the dealer. About $110. yes, a little disappointing

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                        • #13
                          Sounds reasonable but I live on a ski lake where we fill with 5 gallons cans. And I share the boat with a neighbor. So just filling is not a good option for me. Before I started sharing it wasn't a big problem. Maybe you are out of 5 gallon cans and want to ski 2 quick sets. Do I have enough or do I need to go buy gas? The gauge reading correctly is a better answer for everyone.

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                          • #14
                            I had no idea those were adjusting screws. Mine has two hex head bolts which look structural. I'll give it a shot. thanks.

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                            • #15
                              Originally posted by g-Dog View Post
                              I adjsuted mine last year using the calibration instructions...and it's worked great ever since.

                              http://www.centroidproducts.com/3wire.htm
                              I agree with Dog, One screw will adjust the full side of the reading. Not sure how it would get out of wack, but worth a try.

                              Also for you guys looking for a sending unit, I have a used one from my 99 Prostar 205V. I changed it last year then found out it was actually my gauge. PM me if you are interested in buying one used.

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