Mpg fuel gauge

[The Youngen]

I was just curious if anyone knows of a way to hook up a flow meter to the fuel lines and than have that hooked up to a gauge so that it can tell you how many mpg's your using at any point in time. Obviously it cant measure the average unless it was electronic but i just thought this would be cool. Post any ideas.

[raycow]

This is a fairly common feature on high-end cars. Some of them also tell you miles traveled/gallons used since fill-up and miles to empty at current rate of consumption.

Basically you need to input signals from a flow meter and a road speed sensor to a processor that outputs the result to an analog or digital display. I wouldn't be surprised if some outfit already sells an aftermarket kit that does this. Someone who is decently sharp with electronics could build the needed circuitry, so look at magazines like Popular Electronics or its online version.

Ray

[ray_mcavoy]

It won't give you exact MPG numbers, but a simple vacuum gauge will give you a pretty good indication of the instantaneous fuel economy.

[Longhorn Man]

i highly doubt it can be done on an old carb'd engine

[Fitz]

Originally Posted by Longhorn Man

i highly doubt it can be done on an old carb'd engine

Flowscan makes a gauge that does it for carb'd motors...but to get it to convert from gallons per hour to MPG you need a GPS...it can't work with a speedo.

With Gal/hour all you need to know is how to divide miles per hour by gallons per hour...in your head as you go motor through traffic dodging tourists and little old ladies!

[Wrenchbender Ret]

There used to be a company that made an after market kit that did all that. I had one on a 79 Cutlass I drove for many years. It was great. I tried to find them again & they say the co. is out of business. I got them from J'C' Whitney & put them on 2 freinds cars. It was a lot of work putting them on with all the sencers but was well worth it.

[Vintage Windmills]

my 02 bmw has one and pretty much all bmw's from the 80's had one. It is pretty worthless though because it is so sensitive to intantaneous load and jumps all over the place as you would expect. The average mpg computed is so much more valuable since you get a sense of overall efficiency. The instant reading is basically "noise". maybe it would be useful for testing different things but you'd have to be careful to run under the same conditions (stretch of road, wind, temp, operating temp, etc. not to mention be sure you are not slightly accelerating or decelerating. The slightest change in pedal position changes your mpg by 10 or more. Even if you could control everything, you need multiple sample points and an average function would be better. Why do they inclujde it in these cars? I don't know other than its interesting to see just for curiosity's sake

I do like the miles to empty feature

[Ackattack]

I'm pretty sure the BMW gauge is just a vacuum gauge that is labeled as MPG.

I think the only way to do it without being hokie, you'd have to have fuel injection and be able to use the injector pulse width, fuel flow, speed, and a couple other variables to come up with an accurate number.

[The Youngen]

Good point. than does anyone one know of a average mpg gauge that wont look out of place in a 71 ?

[Vintage Windmills]

I've never seen an average guage with a dial; this feature is only part of digital displays. You;'ll have to engineer and build something- would be easier to convert to fuel injection and buy a mileage computer (if someone still makes them)?

[piecesparts]

Back in the early 70s, GM had gauges on their cars that read out in MPG. IT was a vacuum gauge the showed poor mileage when you accelerated hard or did not use the engine that allowed it to stay in an even operating condition. The gauges were the basic round kind with a needle and large areas that were green, red or yellow depending on what you were driving.

[id_unavailable]

look into mpguino. Its a kit (meaning you get a board and pasts that have to be soldered) for newer cars but could be adapted to an old truck. It measures the vss and injector pulse. The injector pulse could come from the flow meter that are used for boats that put out a pulse. A vss could come from a hall effect sensor mounted at the u joint directly behind the transmission. I looked into doing this but the flow transducers are around a 180 bucks.

I was thinking a wideband 02 sensor would be a better investment to tune the truck to save gas.

[stich626]

a tennis ball under the pedal works

[70 shorty]

I think I'd just put a vacumn gauge on it a and be done with it.