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post #1 of (permalink) Old 11-22-2002, 01:43 PM Thread Starter
 
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mpg gauge?

Alright, I will probably never get around to doing this, but I just started thinking about the newer cars/trucks that have those instantaneous gas mileage gauges (or meters, whatever). I was wondering how hard it would be to rig one of these up. I've thought of 2 possible ways to do it, one requiring a signal from the speedometer and the other from the odometer. Both of which I would have to add some sort of flow rate meter to the fuel line. Does this sound anywhere near feasable, or is there an easier way, or is it just a pipe dream? Thanks in advance.
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post #2 of (permalink) Old 11-22-2002, 02:18 PM
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Re: mpg gauge?

Probably the easiest way would be a mechanical linkage from the gas pedal to a gauge calibrated as such:

Full throttle = 1mpg
1/2 throttle = 5 mpg
Coasting = 9 mpg

[img]images/graemlins/smile.gif[/img] [img]images/graemlins/smile.gif[/img]
post #3 of (permalink) Old 11-22-2002, 02:37 PM Thread Starter
 
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Re: mpg gauge?

I was thinking of a more accurate way of doing it by taking the speed (miles/hour) and dividing by flow rate(gallons/sec) then multiplying by the right conversion factor (1/3600) to drop the time increments out and have an accurate, and precise instantaneous gas mileage. The problem is getting something to send the right speed and flowrate by just using sensors and then calculating it without a computer then sending it on to a digi-read out or something. I'm not very skilled in that area. [img]images/graemlins/frown.gif[/img]
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post #4 of (permalink) Old 11-22-2002, 02:54 PM
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Re: mpg gauge?

here's a good string on aftermarket mpg gauges...seems pretty difficult to measure the flow according to this description...

http://yarchive.net/car/mpg_gauge.html
post #5 of (permalink) Old 11-22-2002, 02:56 PM
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Re: mpg gauge?

Neat idea. With a fuel injected vechicle the injector's pulse width varies. You will have to take the pulse width into the calculation to figure out the fuel usage. Is the bronco's fuel system constant pressure? If its not you also need the pressure in the fuelrail to figure it out.

I guess with a carborator you wouldn't need this info. All you would need was a flow sensor leading into the carborator.

I think the easiest way would be using a small microprosessor to calculate and display the data. You might beable to use a "BASIC stamp" micro. This is a processor with built in memory which you can program using BASIC and write the program into it with you home computer.
post #6 of (permalink) Old 11-22-2002, 03:26 PM Thread Starter
 
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Re: mpg gauge?

I didn't realize they had stuff like that (home programmable chips). The coding should be pretty short, maybe 10lines of code or less (never programmed in basic, but I figure it couldn't be much different than c++ or java). I figure if I could somehow sense how much gas was being sent past the sensor then it would tell me just how much was being used up without having to use much else. From that idea, I don't see why I would have to know pressure or pulse length or any of that. Of course I would still have the problem of converting the signal the 2 sensors sent to a number I could use.
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post #7 of (permalink) Old 11-22-2002, 03:46 PM
 
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Re: mpg gauge?

Boats use fuel flow meters all the time, and they can calculate your MPG. Biggest problem is that it's gonna lighten your wallet quite a bit. here is a link to West Marine. They've got them but the cheapest I saw was $300, and I am not sure but I think they require an NMEA interface to calculate MPG (from a GPS or compatible speedo).
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post #8 of (permalink) Old 11-22-2002, 09:26 PM
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Re: mpg gauge?

get ahold of a schematic of a late-model FORD with this feature and maybe you'll be able to figure out how they do it... actually my dad's 90 Lincoln Town-Car had this same feature in a little overhead digital console, so more than likely it's very easy to hook up to our trucks since the fuel injection systems ought to be pretty similar.
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post #9 of (permalink) Old 11-22-2002, 09:32 PM
 
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Re: mpg gauge?

What ? are you trying to depress yourself ! Seriously, If you're just looking for an indicator

Why not use a vacuum gauge ? My brother put one on his car and it came all marked out with areas of green to yellow to red. Nail it and you're in the red, keep your foot out of it, you're in the green,etc.

Simple as heck to hook up and dirt cheap.

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post #10 of (permalink) Old 11-22-2002, 09:51 PM
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Re: mpg gauge?

yeah, a MAP sensor is a good measure, and i think that's what the Lincoln used... that would be insanely easy to hook up and you could probably scavenge a console off an old FORD like that Lincoln

i disagree with Sixlitre, this is a GREAT idea because you'll have renewed confidence in the Bronco's fuel efficiency as you go down hills and see that you're getting 30mpg [img]images/graemlins/cool.gif[/img]
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