Yeah, as RH77 says, my understanding is there are freeware programs that can calculate instant/average MPG from any OBD2 interface.

Someone on teamswift is using this tool. Inexpensive, and he says it does MPG instant/avg, short & long term fuel trim: $83 + $5 shipping.

https://www.obddiagnostics.com/order.html

You can also order it in kit form and solder it together yourself if you're able and want to save more $.

Looks like the MPG feature is part of the freely downloadable interface you can get here: https://www.obddiagnostics.com/ProgWin.html (Windows ver). Maybe this'll work with your existing physical interface. Worth a try.

Just downloaded and installed the software from the link above. You can operate it in "simulation" mode without the hardware (random values).

Pretty neat. But I can see how I'd like to improve it already.

It does have an instant & averager resettable MPG function, based on either MAF or MAP output. But this function is pretty basic compared to the SG, and I'm not sure it can be fine-tuned (e.g. distance & fuel used calibration).

The guy who sells/writes this lives in TN. I bet he'd make some cash if he got involved at GS and expanded its MPG functionality. He could be a real competitor to the SG2.

asdf

I just won an auction for the Hong Kong unit

I really like that laptop setup. Only problem is now you are going to have a real hard time looking at the road. You cant just put the laptop on your dashboard.

You're right. Now I need a dynamometer!

Thanks for the tips and links. Unfortunately my cars are OBD 1. I'll keep looking for something with a MPG readout. As a closely related substitute, I have a MAF readout on my dash so I can see instantaneous consumption of air, which is closely related to fuel consumption as you know. I did a quick experiment with it one day- I was cruising on the freeway at a constant 65mph and noted the airflow was about 150 Hertz (it's a frequency based airflow sensor) Then I put the car in neutral and revved the engine until it showed 150Hz again. The revs stabilized at 5300rpm. So it takes just as much fuel to push my car down the road at 65mph/2400rpm as it does to spin only the motor at 5300rpm. Blew me away. I was a believer in shifting at low rpm after that.

I wonder what sort of tests MetroMPG will come up with using his new logger? Any plans yet?

BTW one of my loggers is called Pocketdyno because it has a built in dyno program. Yes, it's cool and yes, my loggers are all 1/4 mile oriented.

Getting a standalone would of done the same thing with your mileage. It's a computer based system and it fine tunes so good that one of the side effects is better fuel economy. You should of just gotten a megasquirt.