Fuel consumption display

[sirvo]

The consumption meter won't work as you have it described. I've tried it ('98 Nissan and '01 Dodge). The numbers end up out in the weeds.

TPI, multiport, (sequential fire, batch fire, doesn't matter) etc. fuel injection systems have a fuel pressure regulator referenced to manifold vacuum which means the rail pressure changes as the manifold pressure changes. Now, yes, this does mean that the pressure across the tip of the injector remains relatively constant, but it's not nearly as precise as a person would think.
Then you have to throw in the fact that most autos don't spend all of their time in perfect closed loop. Hit the gas, and you're burning roughly a 12-13 to 1 Air/Fuel ratio, get off the gas for a stop sign and you might only be burning 20 to 1, idling will tend to be on the rich side of stroich (14.7:1).

BUT! Don't let all of that negativity stop you! It's a fun project to play around with. And as I learned, you get to play with figuring out how to hook up to various inputs, condition the noise out of them, and do math in the relatively restrictive environment of a PIC. Even if the fuel meter part doesn't work so well, you can log your speed, rpms, pulse width, etc. and look at it later to see what you were doing. Just don't forget to keep your eyes on the road while you're testing the system, and not on the LCD to see what's going on!

JDG

Hello you All..

Skimask, are you there?

I built my car fuel consumption and something is not going well. It works like this:
The software does the measuring of the injector's on_time and also the distance run. TMR1 ticks every 100us and the injector's on_time keeps being added up by 1 at each tick in a WORD variable. The distance is also being added up in a word variable. (my car 'distance' sensor ticks 8,31 pulses per meter). The software keeps counting both ticks and on every kilometer (8310 pulses) it does the math and calculates the km/L by a running average of 10km.

So, the thing is. When driving at a low rate of speed it shows a very low km/L. When driving at high speed, it shows a very high km/L. For example: Driving in the city, it shows 5~7 km/L (it should show 7~9 km/L) and driving at the roadway, it shows 13~20 km/L (it should show 9~11km/L).

I read what you wrote about pressure's difference and stuffs like this. But, what I can not understand is: Isn't the injector's on_time proportional to its output? Do you know why this is happening?

It would be great any tips now..

Thanks in advance!

Regards.