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  1. #1
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    300xs Fluctuating fuel burn

    I bought a boat with a 2015 mercury 300xs that was recently rigged on my new to me LCB cat. It was upgraded with a new simrad and vessel view. The 300xs has just under 200 hours and runs great, but I noticed my fuel flow numbers have been bouncing up and down at a steady rpm. For the first 5-7 hours I was seeing 15 gallons per hour fuel burn in the 4200 rpm range running 65 mph. Now I am seeing the fuel burn jump around from 14-21 and doesn't seem to settle down. I also have a water pressure sensor error where the water pressure goes to 0. I replaced the sensor with a new sensor and it was working, but is now going in and out. I rigged a manual gauge to check the water pressure and I do in fact have good water pressure. The boat runs good and is not showing any issues while running. Could these issues be due to the new vessel view/ simrad setup? Perhaps a firmware update issue?

    I called the local mercury shop, but they can't look at it until December so trying to work out the issues myself because the boat is running fine. Rpms, temps and gps are all holding steady with no issues.

    Has anyone heard of any issues like this? Ground issue, network issue? I think the simrad is a simrad go.

    Thanks in advance

  2. #2
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    It could be a shared 5v reference with the water pressure going crazy as well. Maybe it is shared with the MAP, coolant or air temp sensor this would have a big affect on fuel burn.
    TJ @ Baker Engineering
    Tuff 24 300xs
    Tuff 16 90 Yammie
    3.75@199mph with LSX power!!!

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  4. #3
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    Formerly Central WI/LOTO Currently PHX AZ
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    I think hellbents is onto something…it’s probably time to get it to a dealer and get a log of what’s going on.

    My guess is that your 5V power supply is fluctuating or getting pulled to/toward ground, and muddling up the signal to TPS and MAP sensors, which your engine is using to calculate load/fuel demand.

    If neither trim nor RPM are fluctuating but your fuel flow is, something is rotten in Denmark…
    A problem is only a problem when viewed as a problem...

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