I can address this question because I actually built my own from scratch for my college senior project (electronics engineering).
The MPGuino and similar products measure MPG differently than the ScanGauge and those types of products. The primary difference is that the SG assumes a constant air/fuel ratio that is the ideal ratio for gasoline engines. Then with that info they measure airflow into the cylinders as a way to estimate how much fuel is being used. Then they use distance data to calculate MPG.
With my project and the MPGuino, we use the injector signal and speed sensor to calculate MPG. In fuel injected engines the computer (ECU) tells each injector when and how much fuel to deliever in the form of a pulse. By measuring the duty cycle of this pulse and knowing the size of the injectors (ex. 180cc or 240cc) you can estimate how much fuel is going into the cylinder. Then just add in distance data from the VSS to calculate MPG.
The latter method is a little more accurate because the air/fuel ratio will change slightly in all cars but especially in a lean burn engine (which is why I made mine this way, I drive an HX civic). Even if the air/fuel ratio changes it doesnt effect the calculations. You cannot use a ScanGauge accuratly on an HX because it assumes the perfect air/fuel ratio but on an HX it changes when in lean burn. With the MPGuino and mine, you need to properly calibrate the VSS data by knowing exactly how many pulses per mile your speed sensor uses. This info is readily available for most cars but you can fine tune it using GPS.
Quote:
Originally Posted by fastegg
Ive sent lots of messages to addresses asking about the MPGuino. Nobody
seems to have one and nobody seems to know where to get one.  |
It seems they are all out of stock on the main websites. I just searched MPGuino on google and found places selling kits and assembled units. Heck maybe if the MPGuino is dead I will start selling mine lol