fuel economy estimate

I've had a request for a fuel economy estimate on the datalogger that I wrote

anyone else done this kind of calc and have some advice?

am I foolish in my assumption that inj. pw multiplied with a constant representing fuel sprayed per pulse would be the best baseline? (I think that's how EE vettes did it)

obviously should reference map so I can scale for fuel pressure variation too (vac reference regulator and all)

or should I be thinking more along the lines of maf afgs @ 14.7:1 and say ???? when it's not in CL

Take a look at my $42 and I think $0D has one too.

cool, thanks man I will!

how were the results with yours, on a scale of useful to lightshow?

It was very useful when dialing in your highway or other cruise speeds for MPG.

Overall? I never really tried to build a spreadsheet to come up with an overall MPG to match what fill up at pump does...

the equations i use make accurate instant MPG calculations, but "trip" calcs..... i haven't mastered that yet. i can get accurate trip distance, but not fuel usage.... ?

the way GM did it starting in ~87 or so for the DIS/DIC units works pretty well for trip calcs. three significant values are sent to the module for use, vehicle speed, a running total of how long the injectors have been open and an injector flowrate value. those are the only three things needed for an accurate distance and fuel usage calc. depending how you want to impliment cylinder/injector count, that could also be important.

vacuum/MAP is irrelevant for injectors that shoot into a vacuum(or pressure) and have a vacuum referenced regulator, since the pressure delta should be consistent on both sides of the injector nozzle, keeping flowrate identical(or very close to it) due to changes in vacuum.

if you had an injector scheme that shot into vacuum with no vacuum-referenced regulator or a scheme that had a vacuum referenced regulator, but shot into atmospheric, then you would need to perform vacuum correction.

yeah you're right about vac. ref i wasn't thinking clearly about that one

i think i might throw speed right out, and call this instrument a walletometer, with the only displayed metric being a dollars per minute of fuel consumption, to scare you off of keeping your foot into it....

(it could query the 'net to update for local fuel prices on my car pc too)