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Mercruiser issues with alarm and guardian mode

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  • Mercruiser issues with alarm and guardian mode

    I have a 2007 Mercruiser 496 8.1 with bravo 3 and has 130 hours. Also has a closed cooling system. I have issues with the alarm going off and then going into guardian mode at about 3000 rpm

    Took it to the dealer for a scan and they said it was temp related. It does not overheat. I changed the thermostat. I changed the seawater impeller and housing as recommended. still the same.
    Then I changed the exhaust manafolds and the 2 temp sensors. Also changed the water pressure sensor. Still acts exactly the same. Changed the oil and filter and fuel filter also. Motor runs great until 3000 rpm.
    What else can make that alarm go off?
    Thanks for any help

  • #2
    I did hear of someone with a restriction in a check valve that sent most of the water to the manifolds & starved the engine. He was getting an overheated engine that was visible on the gauges & an alarm due to lack of flow & associated heat. I mention this as apparently the check valve is not shown in all diagrams -- But again the gauges should show a temp rise at times if that's the issue.

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    • #3
      Have you ohmed the CTS ? Might be sending a false reading to the ECU about the overheat
      1999 Powerquest 260 legend
      502 mpi
      B1

      Comment


      • #4
        Originally posted by wellcraft-classic210 View Post
        I did hear of someone with a restriction in a check valve that sent most of the water to the manifolds & starved the engine. He was getting an overheated engine that was visible on the gauges & an alarm due to lack of flow & associated heat. I mention this as apparently the check valve is not shown in all diagrams -- But again the gauges should show a temp rise at times if that's the issue.
        I inspected the check valves when I had the manafolds off. They looked good.

        I am not having a overheat issue and the manafolds are cool to the touch.

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        • #5
          Originally posted by scoflaw View Post
          Have you ohmed the CTS ? Might be sending a false reading to the ECU about the overheat
          No I did not. I will change that sensor and see. What other sensors might trigger the alarm? I feel like changing them all. My thought are a bad sensor somewhere.

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          • #6
            So you cleared the overheat code and it returns ?
            1999 Powerquest 260 legend
            502 mpi
            B1

            Comment


            • #7
              Took it to the dealer for a scan and they said it was temp related. It does not overheat.
              Without an actual code being thrown (no mention of code from dealer) I'm skeptical that its temp related. Being close to 3K rpms the ECM may think your not in gear. Look on the shift plate and see if you have the gear switch in the pic

              Click image for larger version

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              94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
              95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
              07 Seadoo GTX
              Merc Adults Only VP Adults Only
              G-Dad always said "First Liar doesn't stand a chance"

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              • #8
                Originally posted by scoflaw View Post
                So you cleared the overheat code and it returns ?
                I don't know how to clear the code if it even has a code. nothing seems to be over heating.

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                • #9
                  Your dealer said it was temp related. You should find out what he saw to make that statement. That ECM will store codes, and you need the scanner for more info. You will be able to monitor the temp on the tool and compare it to your gauge or an IR gun.
                  1999 Powerquest 260 legend
                  502 mpi
                  B1

                  Comment


                  • #10
                    Originally posted by scoflaw View Post
                    Your dealer said it was temp related. You should find out what he saw to make that statement. That ECM will store codes, and you need the scanner for more info. You will be able to monitor the temp on the tool and compare it to your gauge or an IR gun.
                    He just told me to change the impeller and housing then go from there.

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                    • #11
                      so I changed the CTS and temp gauge sender. Same results. I put an IR gun on the manafolds 137 degrees on the manafolds and 150 on the elbows @ 3200 rpm on muffs and in gear.

                      I will test that shift switch. I think Im going to buy a scanner Any recommendations on that?

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                      • #12
                        I have a rinda, the merc scanner may be better.
                        1999 Powerquest 260 legend
                        502 mpi
                        B1

                        Comment


                        • #13
                          Rinda makes the one Merc uses, just has there label on it
                          http://www.rinda.com/marine/marine.htm
                          94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
                          95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
                          07 Seadoo GTX
                          Merc Adults Only VP Adults Only
                          G-Dad always said "First Liar doesn't stand a chance"

                          Comment


                          • #14
                            I have that 2nd tool in AD's link. Not the best IMHO. Should be good enough to figure out your problem though. Make sure you get it with the 555 adapter you'll need.
                            1999 Powerquest 260 legend
                            502 mpi
                            B1

                            Comment


                            • #15
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                              Ok I purchased a Techmate Pro scanner. played with it for awhile. wasn't giving me any worthwhile info.. I few minor faults that have nothing to do with my motor. I cleared all faults and run the motor. 2800 rpm in gear. all good. manifold temp is about 10 degrees hotter on port than starboard. Reved to 3300 to get an alarm and to go into guardian mode. now gives a fault seapump block/low pressure. I already changed that sensor so might be something in the line. Maybe the checkvalve in the manafolds are bad? Anyway I think I'm going to take all the lines off and clean/ check everything from inlet to outlet. and change those check valves. Any other suggestions? scanner is awesome by the way!!!

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