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Real-time MPG display for vehicles

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HarveyH42

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Gas prices are on the rise again, and it got me to thinking. I remembered a device from the 70s, that calculated MPG, but don't remember much about the details (wasn't driving yet). Seems like there must be a simple and cheap way to measure the flow rate of the fuel, and distance traveled, pretty simple calculations, and a 2 digit display should suffice (unless you install an HHO system :) ). The point being, that changing your driving habits, can dramatically reduce fuel consumption. If you see the numbers rising and falling, you can quickly learn what to avoid, and how to improve.

I don't know if I'll get around to building such a gadget, have quite a backlog of things to build, and in the works. Figured posting this might give a college kid something to turn in. Or maybe somebody looking to make some quick cash, since if it's cheap enough, and easy to install, plenty of people would jump on it.

Mostly, I guess I'm a little curious about whether modern cars already have the input information already available. Who knows, maybe it's already installed in those fancy new cars (mine is a '91 Explorer, gas gauge doesn't even work), lots lights, bells, and beepers...
 

tcmtech

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If I am remembering correctly the device you are referring to was most often a vacuum gage of sorts. I have seen a few of them as factory installed gage sets on the older mopar vehicles. They were labeled in both inches of vacuum and MPG. The lower your vacuum reading the lower the MPG.
I have been to a number of mopar classic car shows and a couple of my college buddies were the ones that got me to go and see their cars. They had the MPG gage sets and said they seamed fairly accurate.
 

tcmtech

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In theory I would think that by using a micro controller of some type all you would need to do is read the fuel line pressure and the PWM of one of the fuel injectors to be able to calculate the fuel used per unit of time. Your local dealer should have the exact fuel per unit of time rating on hand. Usualy fuel injectors are rated at pounds per hour, I think.
Once you know how much fuel you are using then all you would need is to read the signal off of the speed sensor and add that to the calculation.

If your going to run a HHO gas booster you may need to add a extra input from a switch that will change one of the program multiplers and make the display read at a 8 - 10 times higher number! ;):D

So when someone is riding with you then you can flip a switch and say you just turned the HHO gas system on and all of a sudden the MPG readout will jump way up too! :D
 

HarveyH42

Banned
I was thinking of something simple to setup and install, cheap to build. Something most anyone could afford and install themselves. Would need to be very precise, since the important part would be the changing numbers. High number = good, low number = slow down and quit showing off...

Would be just the thing for the HHO guys though, would leave much room for debate, with the numbers right in front of them. But like I said earlier, your driving habits can have a huge impact on economy. Traffic lights aren't starting lights at a race track, you don't have to floor it, just to see how far ahead of the other cars get. Same with passing other cars. Taking a route with few starts and stops also helps. Sometimes the longer drive actually takes less time and fuel. Not sure :), but think using a cellphone will driving, also wastes gas, so pull it over to gossop you sissies. Don't own a cellphone, so will never know. Reading these tips usually has little impact, but seeing the results on your dash is pretty convincing. Usually when the fuel demand drops, the oil companies lower prices. They don't want to scare their customers into making any drastic changes in their consumption habits.
 

picbits

Well-Known Member
All you need is to measure the pulse width of an injector via a CCP input on a PIC microcontroller and the speed of the vehicle.

I've got a product under design which includes this but its a long way off being available to the general public yet.
 
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Or just keep your foot off the gas. I've a brother who is the king of the mpg. Accused him of making 'mileage runs' when caravan-ing. Slow acceleration from stop signs, backing off to 50mph on open two lane roads, it's extremely frustrating when in this mode. But hey, you have plenty of time to soak in the scenery.
 

tcmtech

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All you need is to measure the pulse width of an injector via a CCP input on a PIC microcontroller and the speed of the vehicle.
Plus many auto manufactures use a variable fuel pressure system.
Ford has a vacuum based pressure regulator on most of their fuel injection systems. As the engine vacuum varies the fuel line pressure also goes up and down.

I have many old fuel injectors lying around and everyone came off a different size of engine. The volume rates and working pressures are all different too.

Thats why I mentioned that the fuel pressure would need to be monitored and the actual rated fuel flow of each size of injector would have to be manually calibrated to get an acurrate reading.

But it is easily doable!
 

picbits

Well-Known Member
It makes me laugh when the Americans talk about economy.

Over there, hitting 20mpg seems an achievement. Over here anything above 50mpg is considered economical.

We are currently driving a car with a 2.0 Litre engine, 140bhp, 305nM Torque (225lb/ft) and a top speed of 127MPH. It can do 0-60 in around 10 seconds which isn't fantastic but .......

It can easily get 63 miles to the gallon.

Attached is a picture - can anyone guess what it is ?
 

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tcmtech

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YEA... Well how come our vehicles get such great mileage when used over there and yours get such crappy mileage when ran over here? ;)

Think our big oil industry doesn't have something to do with it! :D

Plus you do build stuff for efficiency and durability because you have actual manufacturing competition!
Over here our manufacturing giants figured out that if they all work together and build equal crap they can get equally big profits while not actually having to resort to making better products! :eek:

I know for a fact a new school bus weighing around 22000 pounds with the Mercedes engine gets about the same mileage as a standard half ton pickup that weighs 4600 pounds ! :eek:

SO lets see you argue that one! Um.. no.. wait, What point was I trying to make?

Oh ya, WE ALL READY KNOW WE ARE GETTING SCREWED! so there! :)
 

Sceadwian

Banned
I'd love to have one of those picbits, unfortunately they don't sell them here in the US, there are any number of a dozen reasons for it.
 

gabeNC

Member
It makes me laugh when the Americans talk about economy.

Over there, hitting 20mpg seems an achievement. Over here anything above 50mpg is considered economical.

We are currently driving a car with a 2.0 Litre engine, 140bhp, 305nM Torque (225lb/ft) and a top speed of 127MPH. It can do 0-60 in around 10 seconds which isn't fantastic but .......

It can easily get 63 miles to the gallon.

Attached is a picture - can anyone guess what it is ?

Ford Focus?


I have a 85 mile (137 kilometre) round trip commute. I love where I live, so I pay the commuter piper. I would give my left nut for a 60mph car. I'm done having kids so it really wouldn't matter.

My 2.4 litre little Dodge Stratus gets about 32. The closet thing (that I can think of... feel free to add/correct) on this side of the pond that gets really good mileage and still has 4 doors and enough space is a VW diesel jetta. They get around 50.
 

tcmtech

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A older friend of mine had a late 80's 3/4 ton Chevy diesel pickup that the engine went bad in. His neighbor at the time was a very good machinist. He made an adapter plate and parts to retrofit an industrial Volvo engine into the Chevy truck.

He swearers the industrial Volvo was rated at 40 hp less than the factory engine but had far more driving power and almost double the fuel mileage!
He claimed that it routinely got mid to upper 30's fuel economy empty and 20 plus pulling a big trailer.

He still talks about it and wishes he would have never sold it. His new 3/4 ton Ford diesel is lucky to break the 10 MPG mark empty, and half that loaded!
 

picbits

Well-Known Member
Ford Focus?
Nope - guess again.

You might be rather suprised.

Oh ya, WE ALL READY KNOW WE ARE GETTING SCREWED! so there! :)
Hmmm talking about getting screwed ....

We're paying on average around £0.95 for a litre of fuel. That equates to around £3.61 per US gallon. When I visited the USA last year the £/$ was nearly 1:2 so that would be $7.22 per gallon ....

I remember filling up our 3 litre V6 people carrier we hired over there for around $25 :eek:

At the current exchange rates we're paying $5.27 per US gallon over here for regular unleaded.
 

tcmtech

Banned
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Hmmm talking about getting screwed ....

We're paying on average around £0.95 for a litre of fuel. That equates to around £3.61 per US gallon. When I visited the USA last year the £/$ was nearly 1:2 so that would be $7.22 per gallon ....

I remember filling up our 3 litre V6 people carrier we hired over there for around $25 :eek:

At the current exchange rates we're paying $5.27 per US gallon over here for regular unleaded.
Dang! dont let our American oil companies find that out or they will raise our prices to beat yours!
But if I could buy fuel that got twice the milage as what we have I would spend it!

No.. Wait... I take that back...
Thats why I run propane! If built for it, gasoline engines actualy get better milage and still beat every emmisions standard you can throw at them! And its still cheaper than gasline! :)

I have driven over 170k miles on propane powered vehicals I have personaly owned and I know it works super! The oil never gets dirty and the engines always run smoother. Plus without the cylinder walls getting washed down the engines dont ware out! :)
 
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