ptsmith24

Hi, I was reading about your mpguino installation. Im really glad to see more people building these.

Depending on how your car controls the injectors, it is possible that you might be off by a factor of 2 or 4. Mine switches them from the negative side on 2 circuits, 3 injectors each. Since Im only tapping into one of those circuits, with each detected pulse I get fuel from 3 injectors, plus fuel from the other 3 injectors because those fire without being detected. So 6 total with each detected pulse.

If yours switches from the positive side, all the grounds are probably connected and so you pick up every pulse. If it fires 2 injectors at once, then youre off by a factor of 2. If it fires 1 injector at once, youre off by a factor of 4.

If your fuel pressure is lower than stock, that could be affecting the reading. Like say if your pump is weak or your filter is plugging up, the injectors could be pulsing but at times you wont be getting the actual amount of fuel though, so you could actually be getting better mileage than it says you are.

There is still a fudge factor. Mine seems to be reading about 8.5% low for mpg, not too bad for starters. Of course Ive also been having occasional fuel starvation issues, I need to change the filter. Im not going to change my defaults till I change the filter and run a few tanks, becuase that alone might make it a lot closer.

About your VSS signal, does your documentation make any reference to a VSS buffer, or anything? My cars have a really screwy signal from the VSS itself. But it goes through either a VSS buffer, or the ECM (with buffer built-in). The buffer cleans up the signal into discrete pulses, that are connected to the cruise control and speedometer. If your signal goes through the ECM or buffer, try tapping into it after that, you might get a better speed readout. Except for maybe when going slower than 5 mph, mine is great, it is more accurate than my speedometer.