Quote:
Originally Posted by benphyr
Diesel_Dave,
re: "the MAF method tells me I'm getting over 50 mpg."
Is the quoted mpg above an instantaneous or average for a tank?
If the 50mpg is instantaneous: I notice that your mpg average is approximately 32mpg, not up at 50 mpg, but an instantaneous mpg could easily be much greater than the average. Also, if the calibration is only out by a factor of 2 then you are in the range (ballpark) that you can probably calibrate the machine to make it accurate.
You may be reading a zero at idle because the measurement is below the threshold that it displays and so it "rounds" to zero.
Some food for thought and hoping that you can get it to work for you.
Cheers,
Ben.
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The 50+ mpg number was the average for trips (~24 miles).
Unfortunately, the basic version of OBDwiz doesn't give you the ability to calibrate things. Of course, if it's using the MAF method, then it wouldn't matter anyway--the whole principle it's based on (constant AFR) is flawed for a diesel. Sure, you can calibrate a MAF-based method and get close to your real, long-term average FE, but what's the point? By now, I can get pretty close to my real long-term average just by guessing.
What I wanted was a way to compare different shifting patterns & P&G techniques. A MAF-based method will never work for that because of the constant AFR assumption. For example, when P&G'ing the true AFR at idle is easily double or triple that of what it is under load. That means the MAF-based method will overestimate the idle fuel flow rate by 2-3 times, easily destroying any usefulness the data might have.
So far I've managed to do a pretty good job just by watching and logging what the factory-installed trip mpg meter runs. It reads 10-15% high on average, but that 10-15% has been fairly consistant. Just a loggable, instantaneous version of that would be nice. Apparently the OBDwiz software can't access the same information that's going from the ECM to the in-cab display.
Oh well, I'm still pursuing a few more options for getting the info.