Mercury Systemonitor Fuel used question

[jgd2305]

2005 Optimax 250 XS Serial number OT998654. My boat has the square shaped Mercury Systemonitor gauge. It shows some useful information, such as fuel used, rpm, and trim. I am most interested in figuring out how it determines fuel used, and how accurate it is. Does this unit use some kind of sensor and sending unit from the fuel tank, or is it based off some mathematical calculation of my engine size, rpms, etc.? If it's based on a calculation, it seems like I should fill the tank (55 gallons), reset the fuel used, then check the reading against how much fuel it takes to fill it the next time I fuel up, and I can have some idea of how accurate it is.

Thanks in advance!

[EuropeanAM]

Usually VERY accurate- to within 2% margin in most cases.

Many use this feature instead of a fuel gauge.

[SilverFox579]

There is no "adjustment" for "Fuel Used". The data comes directly from the PCM's fuel delivery tables

Quote above from Don's reply to a similar question in the 'Mercury motors' forum.

FWIW, I use my Mercmonitor as Don described and when I refuel gallons pumped have always been within 1/2gal of the displayed fuel used.

[jgd2305]

Thanks guys, so the data comes from the Motor itself, and there is no sensor or sending unit at the tank?

[EuropeanAM]

Fuel used has nothing to do with "fuel level" (two different features).

Fuel Used: From the PCM (based on how much fuel it's told injectors to supply).

Fuel Level: Optional Fuel Harness attached to boat fuel sending unit (eliminates any analog fuel gauge when installed).

[jgd2305]

Thank you guys, one last question:

If I bought Smartcraft Connect Mobile and wanted to monitor my "Fuel Used", would I need to have the app running on my phone the entire time that my engine was running in order for it to be accurate? I'd rather throw my phone in a waterproof storage tote in my boat and not have to look at it or use it if I don't have to.

[EuropeanAM]

Honestly never tried that- but keep in mind that the SC Connect MOBILE (like all of the Smartcraft Systems) is a LIVE communications device (like a gauge or an instrument). While it has SOME historical features, those are only because the app was live, and the phone had an internet connection, permitting data to be saved to your account.

[jgd2305]

Great, thank you again for the information!