Problem with Garmin fuel sensor

[dpod2003]

I have twin 90 Hondas on my 25 Cruiser, with a Garmin GFS 10 fuel sensor for each engine. They have worked well for a long, but just recently they are showing readings that are about double (in a good way) the usage of fuel.
I updated the Garmin chartplotter, and that didn't make a difference. The next step would be for me to take out each sensor, and try to blow out any possible sediment that could be in there.
Has anyone ever had this problem? Any advice?

[gulfcoast john]

Even if there is roughly equal trash in your gas tank(s), it would be really odd if BOTH engines ABRUPTLY show TWICE the prior efficiency on the SAME DAY. So check your display settings to ensure you didn’t fat-finger it to display ONE engine MPG when you previously showed COMBINED or some similar option.
Garmin GFS-10 sensors each come with a gas filter that can get clogged and should be changed at least annually, or sooner, just like your main Honda engine gas filters. The Garmin filters pass larger contaminants and are therefore recommended to be placed BEFORE the main engine filters (which get the small stuff and water).
I didn’t use the small Garmin gas filters and placed the sensors AFTER my Yamaha filters/water separators.
I’d suggest removing the old Garmin filters if they are BEFORE your Honda filters, and replacing both Honda filters as your cheapest most expedient likely fix. There is no Garmin approved procedure to ‘blow out’ the sensors vanes. If they are shot or aged out, so be it. (PM me if you want mine at half price, and un-used Garmin filters, since I later hacked the engine ECM output onto my Garmin N2K network for my fuel info instead of using the GFS-10’s for my fuel computations).
Very interesting, hope you figure it out!
Best,
John

[dpod2003]

Thanks for the help, John. Did you mean to replace the Garmin filters, or to just remove them, as I have Racor filters between the sensors and the engines?

[thataway]

All of the fuel flow transducers are similar--and several "Marine" brands are made by the same subcontrator.

I have had 3 different brands, and all say to install a filter before the flow transducer (which is basically a turbine with small magnets moving in a coil to generate current.) Usually these filters are just a screen or fine mesh--but some have put 30 micron racers before the transducers.

There can be "gunk" build up, which slows the turbine rotations and thus less current--reading low. Or there can be a problem with the magnets or coil. The bearings are just simple sleeve, so they can also wear out in time.

I certainly would try blowing them out, with compressed air (probably limit to 10 PSI, and then slowly increase to maybe 20 PSI. You might also consider using a fuel solvent, such as carburetor cleaner. BUT be sure that what solvent will not damage the plastic housing or turbine blades--and ruin the entire turbine. Many plastics are solvable in carburetor cleaner. There are other cleaners which may be less "corrosive" to the plastics.

Install very fine mesh filter before the transducers. Be sure the "arrow is up" on the transducer., Recalibrate the fuel used after all of this has been done.

There are instances where both transducers could be affected--such as a load of bad fuel...If that is the case, or there is a lot of sediment in the tank--then the fuel needs to be filtered and polished..

[Marco Flamingo]

There is a second type of sensor that uses blades and light to measure. Tiny impeller blades (that appear to be mylar) rotate from the fuel flow and either block or reflect an LED light. I had one go bad and could see the little blades down inside. I gently blew air in and could get it to move, but not freely enough to work again. The unit was completely sealed and it would be like repairing a butterfly wing, so I just bought a new sensor (which are now no longer available for my Faria unit).

I suspected that there are far fewer sensor manufacturers than brand name gauges. The problem is finding which generic sensor works with your brand of gauge. A company called Digiflow offers a selection of flow sensors for various liquids, including fuels, and they are surprisingly inexpensive. Unfortunately, they don't have a cross reference manual like for oil filters at the auto parts store.

Mark