On aircraft, it is not unusual to have an instrument that displays fuel consumption in gal/hr, lbs/hr, or ltr/hr. The digital versions can also sum the total fuel used over a given period. The flow is measured directly with a paddle wheel or turbine device intalled in the fuel line. While the AP or Scangauge or any OBDII-based equivalent can give an mpg reading, it's a calculated value using an inferred number for fuel flow rather than a measured one. Powerboats can also be found with fuel flow instruments.

When tuning for highway economy, it would be a help to know fuel consumption without having to blow thru a tank of gas or two in order to get a trustworthy number.

Has anyone here installed a fuel flow instrument? If so, which kind and to what success?

TIA.

 

Because they can't easily determine exact mileage like you can in a car. As soon as you start trying to use instantaneous mpg readings you are in trouble because there are too many misleading factors affecting short term results. Thats why avg tank fuel consumption is used. Don't forget to account for your tire size in the odometer reading if it's different than OE

 

Thanks Team, but the scheme I had in mind is a bit different. Set up say a 70 mph cruise, zero the totalizer, run 15 miles down the expressway, record fuel used. Then do it the other way. The aviation versions claim to be good to 5% out-of-the-box and 2% with calibration.

Yeah, any instantaneous reading is pretty useless, but even setting up a "trip" on a Scangauge won't work because it's using the same parameters one is may be tuning in its calculation of a faux fuel useage.

 

I guess I would have to ask ...WHY? What information are you looking to collect or view?

 

I'd like to be sensitive to small changes in engine efficiency without a lot of doubt or ambiguity. As it is, even a magic mod that got me 15% better mpg's would be difficult to conclusively detect using mpg's determined from filling the tank and dividing miles travelled by gallons used. Conditions vary too much over the course of burning enough fuel to reduce the uncertainty of defining what a full tank is. Getting that 15% with 3 mods each giving 5% is nearly impossible in a rational way. Ideally, I'd have a brake chassis dyno in my garage, but I haven't won the lottery (yet).

Here's one example from aviation: FC-10 Fuel Computer
It has more features than I need, however, and works over a flow range about 4 times too high.

Edelbrock sells a turbine-type flow meter in the right flow range for only $1700.

This one for boats (Faria) is the closest to what I'm looking for at a reasonable price: Fuel Manager

 

Again, in order to determine *accurate* small changes in efficiency you need a much greater magnitude of data. What you are proposing is not a feasible way to do it accurately. It's just not that simple.

 

why wouldn't you log injector duty? along with Rpm, and some kind of load measurement you could build some kind of measure.

actually team is right, no matter how you choose to measure fuel flow, you will still need to blow thru a tank or three to collect the data and figure out how to interpret it.

 

Which injectors? What if you change injector scaling? Load depends on all kinds of stuff such as how you scale the MAF or alter VE. If one is fiddling with the tune, the changes in the tune itself can change the calculation of mpgs, without the real mpgs being changed in the same way.

Not really. Cruising along in an airplane equipped with a true fuel flow meter, I can fine tune mixture, prop rpm, and sometimes ram air settings and see within a couple of minutes whether the fuel efficiency is better or not.

 

i was thinking injector duty might be an easier way to measure fuel flow, but i guess we're indirectly measuring that as well?

actually since we know how big the fuel pump is, you could build some sort of voltage vs flow map of the pump and just go by pump voltage. its a little like measuring EGT with an o2 sensor, but it might be close enough

 

The fuel pump pumps far more fuel than is used. While not a full 2-way system, the excess is bypassed before it ever leaves the tank.