Any ideas on how to accurately measure mpg’s on an older car with a carburetor?

[Old Tele man]

...so, you're converting "pulses-per-unit·time" into "pulse-width modulation" (PWM), correct? Is that what the display uses?

[TheTestPilot]

you get pulse width variation by default on my circuit ,(so you need to count the 0 volts "on" time of the output) , which is the same as a fuel injector signal but a lot less pulses & that is where my problem lay ,with the sensors I have previously tested .
The speed sensor I assume just counts the change from 12 volts to 0 volts & not pulse width.

Still no hot weather to test vapour issues ,February is traditionally the hotest month here ,mostly high 30's so here hoping.

[Superturnier]

Originally Posted by TheTestPilot

you get pulse width variation by default on my circuit ,(so you need to count the 0 volts "on" time of the output) , which is the same as a fuel injector signal but a lot less pulses & that is where my problem lay ,with the sensors I have previously tested .
The speed sensor I assume just counts the change from 12 volts to 0 volts & not pulse width.

Still no hot weather to test vapour issues ,February is traditionally the hotest month here ,mostly high 30's so here hoping.

Greetings from the opposite side of the globe!
February is usually our coldest month here. Now we have -15*C and plenty of snow.
I took this picture once I was coming from work by bicycle.


Thanks for the schematic! I might use that for my speed sensor.

I think you are right that you can get pwm from your fuel sensor since paddlewheel speed will wary. But I would think it would be more accurate, if you could modify the MPGuino code for counting the amount of pulses.

[TheTestPilot]

Hi Superturnier
Yes , I agree with altering the software to suit the sensor ,but from a previous post ,I have read , that isn't going to happen anytime soon ,unless of course , I learn something about writing software ,I would like to , if I had some more free time.
I was hoping ,to come up with a simple solution , so you can swap the mpguino between Fi & Carb vehicles .
The weather here is similiar to Los Angeles, -15 too cold for me ,even in car.

[Superturnier]

I have done some small modifications to the MPGuino code to suit better for my needs, but nothing big. Mainly copy +paste things.
Although I do automation software for my living I'm not so familiar with the MPGuino language. I guess it's some kind of C+ or something. I wish I could learn it more, but my free time is also too limited

I agree, many times it's best to keep things simple. It would be nice to have a solution also for the carburetted vehicles.

[TheTestPilot]

This is the latest mod to my fuel sensor ,it now has 4 hall effect sensors .
I am hoping to improve the output at idle ,for a steady gph reading .
The 2 sensor version seemed to be consistent as far as final tank readings go ,but the instant display was all over the place.
will do some tank testing over the next week.

[TheTestPilot]

Update for the previous mod to my flow sensor.
This sensor , I am now sure ,that they have got the rating confused & it should be rated at 2-30 litres a minute not 2-30 litres an hour as the data sheet states .
After much modding of this sensor ,I am going to call this one not suitable at this time as we need something that is simple .
I am looking at other methods to measure the fuel flow,including the sensor from Conrad.de .
Tp