GFS-10 compatibility with Honda Gauges on Tomcat 255

[Jhedberg]

Just looking for some input from follks. I'm thinking about installing two GFS-10's on my 2007 Tomcat. I've got twin Honda 150 with the digital Honda gauges (speedo/fuel and then two RPM gauges). I have a 2007 Garmin 4000 series charplotter which looks like the GFS-10 will plug right into but am wondering if I can use the fuel level wire(s) from the Honda speedo/fuel gauge to provide fuel level information to the garmin....any thoughts?

thanks!

[thataway]

The GFS should work fine with your chart plotter. I doubt that the level will work--you have to be able to interface the CanBus system of the Honda to eh NMEA 2000 of the Garmin, thru the NMEA 2000 backbone. The person to ask might be "BlueWaterPirate" on The Hull Truth.

It might work with a Maretron multiplexer. The problem often is the sentencing often is slightly different between Garmin and Honda NMEA 2000. Better probably to use the totalizer function on the Garmin system.

I suspect that since you are running two GFS 10's it is going to be a bit more than just plug and play--you will have to build a NMEA 2000 backbone (I am judging from my experience with Lowrance backbone systems and their fuel flow system--which are similar to Garmin--even though I am using Garmin currently).

See: http://www8.garmin.com/manuals/GFS10FuelSensor_InstallationMulti-lingual.pdf

[beermanPDX]

The GFS 10s will work and provide fuel level when wired to an analog Honda fuel gauge. That is the setup I have with my twin Honda 90s and Garmin GPSMap 740s. The digital gauge may be a different story as Bob points out. The analog fuel gauge is pretty simple with wires for the sender unit in the tank, ignition, ground, etc.

The NMEA 2000 backbone is just a cable, a few t-connectors, and male / female terminators. Garmin sells a "NMEA 2000 starter kit", but you'll need to add another t-connector (2 fuel sensors and your chartplotter) if I remember correctly.

[Jhedberg]

thanks for the great responses! I figured I would have to get a few extra NMEA parts to make the connection to my Garmin. Looking at the wiring schematic for the Tomcat 255 I see that each tank has a sending unit that goes to "the Swicth" I've never been sure what the port and starboard fuel switch on the helm does....maybe it switches the fuel level display on the Honda gauge and since I always fill each tank every time and since both engines use approximately the same amount it doesn't change on the Honda gauge.

Maybe I'm being optimistic but shouldn't the sending units work with a digital or analog gauge? as well as the GFS-10?

what do you think? thanks again!
Josh

[thataway]

You are correct that the port stb fuel switches send that level sensor to the analogue gauge. Something has to convert a analogue signal, to the NMEA 2000 sentences necessary to be displayed on the Garmin chart plotter. The GFS-10 does that. You don't really need to deal with the digital read out in the Honda system--the wires from the tank will go directly to the fuel flow transducer, which does that function. Basically you are forgetting that there is anything "honda" involved--thus not connecting any honda NMEA signal to the Garmin...all is thru the Garmin transducer.

I would separate the fuel sensor output from the analogue fuel gauges and wire into the Garmin GSF directly on each side--ignore the switch--it will no longer be of use. The Stb fuel sensor is put in the fuel line, after the filter, and has to be so the fuel flow is from top to bottom of the vertical sensor. Then you will have to access the top of each tank, and take that respective wiring, as per the diagram in the link above, I would use twisted, wire with foil covering (see what is there to the switch--that may not be necessary...but you do want to have the ignition switch wired in--because you don't want power to the level indicated when you are not running the engine. You might be able to pick up the wire somewhere else than the top of the tank--but you will still have to access the tank top to be sure what the color code is (C Dory has often changed that--may not have in your boat--but check it).

I have not run the Garmin NMEA 2000 backbone, so I don't know if a separate 12 volt source is necessary for the "NMEA 2000 kit"--http://static.garmincdn.com/pumac/2250_TechnicalReferenceforGarminNMEA2000Products.pdf This shows a separate power source--but since the GFS has a 12 volt connection for the fuel gauge, it may be redundant. Also be sure and buy the correct terminator resistors, so there are no open ports on the back bone.

Draw out the diagram, using the above manuals, and double check to see what parts you will need. I suspect that you will need one extra 10 meter cable, and probably another "T" than is provided. Not too expensive, and should work--forgetting about "Honda", because when you disconnect the tank gauge you will no longer get the Honda fuel readings....I would not risk having a NMEA 2000 plus the Honda digital on the same network, which may happen if you do not disconnect the wires going to the honda gauge...(I don't know it will cause a problem--just suspect)

[Jhedberg]

Thanks Bob. I appreciate your thorough response!

I found that the top of each fuel tank and their respective sending units and wiring can be easily reached through the access ports on the deck just behind the main cabin. So now to decide where to mount the GFS-10. Garmin recommends as close to the tank as possible and as you mentioned, vertically with the filter before the sensor. I think I can do this right above the tank but will have to take a closer look. I'll use my multimeter and figure out where and how those wires are switched on at the ignition switches.

I wish I could keep the Honda fuel information but I think you are right that it might cause some confusion.

I already have a NM2K cable running from the back of my Garmin and have GPS and Radar. I don't know if these are are hooked up to the NM2K and so will have to take a closer when I get the chance. Maybe, thinking optimistically again, I already have a NMEA backbone and just haven't spotted it...but if not, building one shouldn't be a problem.

I hate to disable my Honda gauge but the pitot tube sensor at the motors just isn't reliable enough and I wish the Honda gauge provided more accurate information. It seems to average the fuel data using a long frequency so it doesn't respond to speed changes for several minutes.

Anyway, might give it a shot soon. Still very snowy and chilly here but the sun is coming back and hopefully back on the water in a month or so.

Thanks again Bob,
Josh

[thataway]

A decision you will have to make is if you want another filter, specifically for the fuel flow sensors (and this can be a larger pore size than the razor), or to use the razor. I choose to mount the flow transducers between the racor and the point where the fuel line exits the transom to the outboards, thus avoiding a second fuel filter. I have done it with the extra filter in several other boats.

The thought process was that it was difficult to get to a filter near the tank, if it had to be changed. It was also one other potential failure point in the fuel system.

[Jhedberg]

That seems like the most accessible location certainly. I can also mount them up by the tanks but would then have to add the filter. I'm not sure why Garmin recommends they be mounted close to the tanks? Adding a second filter does add another element of unpredictability too.

Some good news, I already have a N2k backbone complete with a yellow power cable at the helm. Amazing what you find when you can get away and do a little looking around!

I'll need to buy a backbone extension cable to make the run from the transom to the helm. I think I still need to power the GFS-10's separately which will be pretty straight forward and tap into the fuel level sending wires, but this should be a fun little project that will provide good information this summer.