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Author Topic:   Northstar F210: Ok for EFI Four-cycle Engines
GreatBayNH posted 02-18-2008 07:52 PM ET (US)   Profile for GreatBayNH   Send Email to GreatBayNH  
I've read on some sites the description of the Northstar F210 that it is for carburetor two- and four-cycle engines. Is this to mean I should not install it on my EFI four-cycle engine?
jimh posted 02-18-2008 08:21 PM ET (US)     Profile for jimh  Send Email to jimh     
My inference is that the concern here is with the fuel injection technique. Most gasoline engine fuel flow instruments use a single fuel flow sensor which is in-line with the fuel supply to the engine. This works well with carburetor engines. Usually the priming of the carburetors is done before the fuel flow sensor is activated, so any fuel manually pumped into the engine for priming is not accumulated in the flow calculations. Once the carburetor reservoir bowls are filled, their float level valves control the fuel flow. Also, most carburetor engines use a fuel pump which is operated by engine crankcase pressure pulses, and thus the rate of fuel flow from the main tank to the engine is always in proportion to engine speed and fuel consumption. However, fuel injection engines sometimes work quite differently.

In a fuel injected engine there often is some recirculation of the fuel. In gasoline engines the fuel recirculation usually does not include returning fuel to the fuel tank. Gasoline fuel injected engines often have a small fuel reservoir mounted on the engine. Fuel which is not used immediately by an injector is returned to the reservoir and recirculated. This design can cause a problem for a fuel monitor instrument. The flow of fuel from the fuel tank to the engine is not always in proportion to the flow of fuel into the combustion chambers. Usually there is a level sensor in the recirculation tank, and if the fuel level in the recirculation tank falls too low, more fuel is pumped from the main tank. When the fuel recirculation tank is nearly full, fuel flow from the main tank is cut back. Often the fuel lift pump from the main tank is an electrical pump whose operation is controlled by the level sensor in the recirculation tank.

As a result, the flow of fuel from the main tank to the engine may be in spurts, and it will not always be in direct proportion to the rate of flow into the engine. In the long term, the two rates will coincide, but they may instantaneously be quite different.

Because of this problem, many engines with electronic fuel injection are not well suited for use with an external fuel flow gauge. I believe this is particularly true for certain Mercury motors. Their fuel-vapor separator assembly contains a reservoir tank with a float switch that controls fuel flow from the main tank, I believe. I have often seen mention in boat test data that these Mercury engines could not be monitored for fuel flow by using the same technique as used with other engines, even other fuel injected engines. From that statement I would infer that other fuel injected engines may not use a large reservoir tank at the engine and might work well with a fuel flow sensor and gauge. For example, the E-TEC engine uses a fuel lift pump which operates from engine crankcase vacuum pulses, so it pumps fuel from the main tank to the engine at a rate which is always proportional to speed.

The instruction manual from Northstar is rather silent on this topic: Downloads/F210-User-Manual/

jimh posted 02-18-2008 08:34 PM ET (US)     Profile for jimh  Send Email to jimh     
There also might be a concern with the rate of fuel flow with some motors. Four-cycle motors often have rather low rates of fuel flow at idle speeds, and the rate of flow may be too low, below the range recommended for accurate measurement with the F210, for some motors, particularly lower power motors which use fuel at a more modest flow rate.

Regarding the spurting flow of fuel from the main tank to the engine with fuel injection on some engines, the "instantaneous" flow rate can be adjusted to compute an average over a longer time. In some cases it maybe possible to increase the time for the averaging to a value which is long enough to even out any spurting in the flow from main tank to engine.

I have found that with my F3100 fuel instrument I had to increase the period of the "instantaneous" averaging to keep the values from fluctuating too much. I believe it was originally set to about ten seconds, and I have increased it to about twenty seconds to get a reading which does not flutter as much.

Again, the long range computation of fuel use will not be much affected by the starting and stopping of the fuel flow with some EFI motors. However, if the idle speed fuel flow is too low, it may not be properly measured.

GreatBayNH posted 02-18-2008 10:40 PM ET (US)     Profile for GreatBayNH  Send Email to GreatBayNH     
Thanks Jim. That's a plethora of information. Detailed as usual.

I did some more Internet searching and there are some Northstar pdf's out there that state it does NOT work with EFI engines with return feed. I assume this to mean it DOES with EFI engines WITHOUT return feed?

Perhaps a CW member that has this gauge working on a 90HP Yama-Merc four-cycle EFI engine could chime in here and give definitive testimonial.


Feejer posted 02-19-2008 09:11 AM ET (US)     Profile for Feejer  Send Email to Feejer     
Seth, this is per the manual for the Fuel Flow Transducer which is a seperate manual from the one Jim posted the link on. "Northstar fuel flow is not for Diesel engines. The are best suited to measuring flow rates between 0.3 to 40 US gallons per hour meaning [two-cycle] and EFI engines from 30 to 300-HP"

I also just got off the phone with the service manager at my local BW dealer. In 2007 they installed them on six boats last year; four were newer 170's with the 90-HP "FOURSTROKE." As far as they know there have not been any problems. When I had [a Northstart fuel flow instrument] on my Sea Hunt the unit was accurate; it was very accurate after I did a calibration.

GreatBayNH posted 02-19-2008 12:35 PM ET (US)     Profile for GreatBayNH  Send Email to GreatBayNH     
Most excellent. I'm moving forward then. Thank you!
fishinchips posted 02-20-2008 07:53 AM ET (US)     Profile for fishinchips  Send Email to fishinchips     
You can install a fuel flow meter made by Lowrance. The LMF-200 will fit one of the holes on the dash. Run the network cable to the transom and connect to your fuel flow sensor in your fuel line. On the same network cable, I run a GPS sensor too. It will give me GPH data, fuel remaining, fuel burn, MPG, and season use.


GreatBayNH posted 02-24-2008 08:25 PM ET (US)     Profile for GreatBayNH  Send Email to GreatBayNH     
I looked at the Lowrance option. After buying the network backbone and connectors it's quite a different cost than the Northstar option.

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