Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - Any ideas on how to accurately measure mpg’s on an older car with a carburetor?

Superturnier · 11-02-2011, 07:27 AM

Those old Zemco units (I have one) can be inaccurate in certain situations.

The fuel flow sensor has an optical sensor that counts the circulation of a small ball in fuel flow. It also counts the bubbles in fuel and if you have a mechanical fuel pump it typically creates bubbles when hot.
Especially when the engine is hot and you're idling at traffic lights the mpg reading goes nuts. But during cruising it can be quite accurate.

Sometimes I have played with a thought that how the MPGuino could be used in carbureted vehicles. At least it would be nice to see the differences in A-B-A testings when you have done some mods.

So, my idea is not to measure the fuel flow, but instead we measure the load of the engine. That could be done with a Manifold Absolute Pressure sensor, which typically give 0-5 volts according to the pressure.

If we can tell the MPGuino that "Manifold vacuum x rpm = engine load" then I think we should be able to see if certain mods will have less load on the engine. But of course we cannot see the real fuel consumption, since the carburettor's fuel delivery is not absolutely linear with engine load.

And to make MPGuino understand the vacuum signal, it would require changing the code or changing the 0-5Volts to PWM (pulse width modulation) and also we should input also the rpm info.

One other option would be using a MAF sensor, which measures the air entering to the engine. Then the rpm information would not be needed, I guess.

11-02-2011, 07:27 AM	#14 (permalink)
Superturnier My way is the low way Join Date: Jun 2009 Location: Finland Posts: 64 MyoldFord - '65 Ford Taunus 20M Turnier 90 day: 27.59 mpg (US) Plastic Spaceship - '94 Renault Espace 90 day: 24.03 mpg (US) Sussu - '82 Suzuki Alto Thanks: 4 Thanked 17 Times in 8 Posts	Those old Zemco units (I have one) can be inaccurate in certain situations. The fuel flow sensor has an optical sensor that counts the circulation of a small ball in fuel flow. It also counts the bubbles in fuel and if you have a mechanical fuel pump it typically creates bubbles when hot. Especially when the engine is hot and you're idling at traffic lights the mpg reading goes nuts. But during cruising it can be quite accurate. Sometimes I have played with a thought that how the MPGuino could be used in carbureted vehicles. At least it would be nice to see the differences in A-B-A testings when you have done some mods. So, my idea is not to measure the fuel flow, but instead we measure the load of the engine. That could be done with a Manifold Absolute Pressure sensor, which typically give 0-5 volts according to the pressure. If we can tell the MPGuino that "Manifold vacuum x rpm = engine load" then I think we should be able to see if certain mods will have less load on the engine. But of course we cannot see the real fuel consumption, since the carburettor's fuel delivery is not absolutely linear with engine load. And to make MPGuino understand the vacuum signal, it would require changing the code or changing the 0-5Volts to PWM (pulse width modulation) and also we should input also the rpm info. One other option would be using a MAF sensor, which measures the air entering to the engine. Then the rpm information would not be needed, I guess.