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Fuel Flow Sensor Minimum Flow Rate
|Author||Topic: Fuel Flow Sensor Minimum Flow Rate|
posted 03-12-2008 08:30 PM ET (US)
I have a 2007 E-TEC 90-HP and a Garmin 535. Garmin is coming out with their fuel sensor that will display fuel flow and MPG. The minimum flow is 2-GPH for the sensor. Will [the GARMIN sensor] work [with an E-TEC 90-HP motor's typical fuel flow rate]? I just want to dial-in the best MPG when I go for a extended cruise.
Explain what a fuel sensor sees.
What data is shown on a display with the E-TEC engine?
Flowscan has one way of explaining [how their system operates]. Lowrance lets you adjust how quickly it refreshes the data.
I think with the rising fuel costs this will help us all with the older engines.
Thanks for any help on the latest systems with their pluses and minuses that can be integrated.
posted 03-12-2008 10:08 PM ET (US)
This topic has been moved to SMALL BOAT ELECTRICAL for discussion.
posted 03-12-2008 10:24 PM ET (US)
If you use an external fuel flow sensor with any engine, the minimum fuel flow rate of the sensors limits the resolution of the fuel flow instrument. If the motor consumes less fuel per hour than the sensor can detect at a minimum, the accuracy of the system will suffer.
I believe that in the E-TEC motor there is data available from the engine control module via a NMEA-2000 interface which can tell you the fuel flow rate for the engine, based on a calculation made by the engine itself regarding the engine speed and the internal fuel mapping. This data is not based on actual measurement of the flow with a sensor, but is data imputed based on a calculation using the engine speed and time. However, such data is not available for a 2007 E-TEC 90-HP motor because the engine management module in that motor is not equipped with a NMEA-2000 network port.
Almost all external fuel flow sensors that I have read about use a small turbine or vane impeller which rotates in response to fuel flow, producing an electrical signal proportional to the fuel flow rate. As far as I know, the design of the sensor and the nature of its electrical signal varies from brand to brand.
In order for any fuel flow sensor to compute fuel economy in MPG, it will have to be paired with a speed input. In the case of an instrument like an electronic chart system with GPS like the Garmin, this computation would probably be made in the electronic chart system computer.
Lowrance has a system which is based on a NMEA-2000 network and employes an external fuel flow sensor. There is no particular advantage in using this system with an E-TEC engine if the engine does not have a NMEA-2000 port.
posted 03-12-2008 10:45 PM ET (US)
Re what can be displayed on a Evinrude I-Command gauge regarding fuel, this excerpt is from the Evinrude I-Command Digital Users Guide, available here on the website:
• Fuel Flow
Regarding fuel flow sensors, none are needed with the E-TEC and I-Command, as implied here:
You can configure an external sensor with the Lowrance LMF-200 or LMF-400 fuel flow gauge. Those gauges operate using a NMEA-2000 network approach to building the link between the sensor and the gauge. The gauge can also read other values from other devices on the network. See the Lowrance documents for more data.
posted 03-13-2008 05:37 AM ET (US)
The E-TEC and its pumps work a little differently. I talked to Flowscan who said while the fuel flow with their instrument will fluctuate and not have an accurate reading the total fuel used will be accurate.
Other people said the the Northstar, Navman, and Lowrance units can be adjusted to balance out the fluctuations.
I already knew about the 2008 models with the NMEA-2000 network port. That is why I was specific to Seahorse about the 2004 to 2007 models. I was also specific in how the unit was to be used. It is a lower cost for people that have the new Garmin units that can use the GFS 10 Fuel Flow Sensor for MPG than to have to buy a separate GPS module and display.
Maybe Seahorse can give more insight if he feels this sender will work OK for the intended use.
posted 03-13-2008 07:07 AM ET (US)
I'm not familiar with the Garmin your describe, but a 2 gph minimum reading is surprising. That means you will not get an accurate reading until cruising speed, and even then it may be uneven because of the vapor separator tank (VST)operation. The vapor tank (as with all EFI and DFI motors) uses a float and valve to limit the amount of fuel and give time for bubbles to rise to the top.
While the motor is running (DFI & EFI) the electric pump gets its supply from the VST and as the fuel level drops, the VST float valve opens and allows more fuel in as supplied by the primary fuel pump (lift pump). This in effect gives an on-off reading to any flow meter installed in the system. At high speeds with more fuel consumption, the on-off times get shorter and shorter. With your 90 E-TEC, fuel flow is as low as 0.1 gph at idle to about 9 or 10 gph tops.
As you know, the 2007 and earlier in-line motors, 90hp and below, do not have the built in NMEA2000 capability, only 2008 and later models. On the motors which do, the EMM calculates the exact fuel flow delivered to he injectors (Merc SmartCraft does the same) and displays the results for the operator.
If the minimum flow was about 0.2 gph instead of 2.0 gph, it would be a much more usable system.
posted 03-13-2008 08:08 AM ET (US)
I don't think there is much difference in the fuel flow rate of a 90-HP E-TEC depending on model years, so it is not particularly significant what model year E-TEC 90-HP is used with an external fuel flow sensor that has a minimum flow rate of 2-GPH; they will all have the same problem with minimum resolution.
Thanks for the notice about the new Garmin GFS 10 fuel flow sensor. However, at a retail price of $216 it seems a bit expensive. I think you can buy the whole Northstar sensor and gauge for less than that. Mitigating the cost may be the feature which allows for connection of an external resistive fuel level sensor. It you have a boat with a resistive fuel level sensor that might be an attraction toward the Garmin.
posted 03-13-2008 06:28 PM ET (US)
Have you tried the Northstar sensor and gauge? Does it fluctuate like Seahorse says?
The gauge is not on the market yet. It looks to be software controlled on what is displayed on the screen. At a street around $150 it would be a reasonable way to go. Maybe there is a way to try one and see? Having that on your map page on the plotter would really be slick. It also would display fuel level. Even if it was not as accurate below cruise settings but did show the proper MPG at cruise It would be a great help setting the throttle for best cruise on that particular day.
posted 03-13-2008 07:13 PM ET (US)
It is surprising to see a low end mesureable flow rate limited to 2gph; coupled to a 3/8" fitting. And I assume by fuel they mean gasoline not diesel.
Why they would put out such a low end fuel sensor seems odd. Because most bigger (and newer) engines have fuel sensors installed by the manufacture. (Especially on diesels becuase the return fuel system.)
It seems to me that this really cuts a lot of the small boat outboard and inboard market out. (Even the my Cummins 270 hp units I have on another boat run down to 0.6 gph at 600 RPM.)
Looking at Garmin's product line, it looks to be expanding into full sensor suites (true wind, apparent wind, Autopilot, fuel flow, etc) all based on a centralized networked system. Which is great.
I wonder how the GARMIN product line is going to expand.
posted 03-13-2008 08:03 PM ET (US)
I have the predecessor to the Northstar devices, the NAVMAN 3100 FUEL instrument. I have written extensively about my experiences with it. But my thirsty V6 two-cycle burns a lot of fuel, so I never worry about the minimum fuel flow sensitivity.
NAVMAN 3100 Fuel Instrument
posted 03-14-2008 07:28 AM ET (US)
"While the motor is running (DFI & EFI) the electric pump gets its supply from the VST and as the fuel level drops, the VST float valve opens and allows more fuel in as supplied by the primary fuel pump (lift pump). This in effect gives an on-off reading to any flow meter installed in the system." - Seahorse
I see this on/off reading on my Navman F3100 which is montoring the fuel flow of my Evinrude Ficht 225s. The reading tends to fluctuate at idle between 0.1 to 0.4 GPH. The meter is set at the default damping parameter.
posted 03-14-2008 08:10 AM ET (US)
The Northstar 210 FUEL instrument (like its predecessor the Navman 2100) does not perform a calculation to deduce miles-per-gallon readings. This is one drawback of that instrument compared to other options available.
posted 03-14-2008 07:11 PM ET (US)
Yes without GPS data your screwed. That is what makes the Garmin enticing if it works. I think I will see if I can get one to try out and report back.
posted 03-14-2008 08:59 PM ET (US)
The speed data does not have to come from a GPS; it could come from a paddlewheel boat speed sensor, for example, and it so happens that NAVMAN used to sell a paddlewheel boat speed sensor for use with their fuel instruments.
The oddity of NMEA-2000 compatible devices is that a fuel sensor which outputs information about fuel flow on a NMEA-2000 network ought to be able to be read by any other attached device which is interested in fuel flow information. It is hard to tell if this is possible because NMEA keeps the details of their NMEA-2000 specifications something of a secret, and only members of their NMEA club get to see underneath the hood of the NMEA process.
If NMEA-2000 were really an open standard, then it would be reasonable to expect that a fuel flow sensor which was NMEA-2000 compatible would be able to inter-operate with other NMEA-2000 devices. You'd think that NMEA-2000 compatible would mean you could use any vendor's fuel flow sensor with any other vendor's gauge that wants to display fuel flow data. However, I would not bet the farm on that being obtainable.
posted 03-20-2008 01:51 PM ET (US)
I also see a fluctuation at low throttle setting on my Navman 3100 which monitors the fuel flow of my BF135.
Has anyone tried to set the damping at a higher rate? The default is set at 5 seconds and the max setting is 99 seconds. I might try to increase the damping from 5 seconds to around 10 seconds to see if this annoying fluctuating goes away.
posted 03-20-2008 04:02 PM ET (US)
I have fiddled with the damping setting on my NAVMAN 3100 FUEL instrument. I think I ended up with it set around 15 to 20 to get rid of the continual fluctuations in the readings when at a steady throttle--and that's with six carburetors.
posted 03-25-2008 06:23 PM ET (US)
When the pump kicks in what is the flow for the 90 E-TEC?
If it is over 2-GPM it would not make any differance as it would be measuring correctly in spurts so to speak. Just another thought.
posted 03-25-2008 09:40 PM ET (US)
The motor would sip fuel so slowly that when the float drops enough to allow more gas into the VST, it would probably take less than a second to replace the amount used. At idle, the lift pump is hardly working at all since the crankcase pulses are so weak.
posted 03-31-2008 11:21 AM ET (US)
Well I ordered one. WM had it at $129.95 with free shipping.
The terminators are 120 ohm resistors so I will make my own harness.
We will see how it works on a 90 Etec. I have to pick up the boat in a couple of weeks so it will not be installed till then. Bennett also gave me a auto tab leveler to try out so that will be installed at the same time.
If I can get an accurate reading of MPG at cruise I will be happy. I will also calibrate it for the fuel level and maybe will be more accurate than my gauge as you can program multiple points of fuel level when filling up the tank.
posted 04-04-2008 08:04 PM ET (US)
Well I got my GFS 10 Fuel Flow Sensor today. It is a complete package including the SD card with the updates for the GPS535s I have. This is the best deal on this unit I have seen so far. $135 clams if it works OK will be a pretty good deal. If anyone needs help with making a harness to connect to their Fuel gauge and CANet on their GPS let me know.
posted 04-04-2008 08:15 PM ET (US)
Seahorse & Jim
Thanks for your help on this. We all want to save money and get the best information from our boats. For the Garmin GPS owners that can use the flow sensor. If it works OK I will do a report on the + & -'s of the system. That way you can decide if it will work for you. My Key West is not a Whaler but it is sure getting dam close if you looked at my pictures. Thanks all.
posted 04-20-2008 09:54 AM ET (US)
I tested the boat out yesterday. It was a little choppy but I was able to get this info from my display. It showed it would go to .2GPH but was intermittent on the readings. Once you get above 2GPH the reading is constant and all the data is displayed. You can go down to .2 to .3 and still get all the data. I think it takes 2GPH to start the turbine wheel spinning and then will continue to turn at the lower fuel flows. Overall it works great and am very pleased with the results. The Chart screen has the overlayed numbers that show the following.
( Top overlay )
( Bottom overlay )
The Information Screen when you press fuel has the following. There is a graph display on the left for Fuel level, Fuel Flow and MPG in the three boxes from top to bottom.
The top box has Cruise Range and Total Fuel on right side.
Thaks for your help on this.
This info is from a 18' with a 90 E-TEC with a 15" prop. The performance should be close to your Key West.
RPM MPH GPH MPG
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