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Old 03-16-2009, 10:28 PM   #1 (permalink)
wagonman76
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Join Date: Jun 2008
Location: Northwest Lower Michigan
Posts: 1,006

Red Car - '89 Chevrolet Celebrity CL 4 door
Team Chevy
90 day: 36.47 mpg (US)

Winter Wagon - '89 Pontiac 6000 LE Wagon
90 day: 28.26 mpg (US)
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Actual mpg vs % that mpguino is off

I have been wondering about this, how to get the mpguino more accurate, so I did some charts with my fuel log data. I charted miles driven, gallons, mpg, % guino is high (from calculated fuel flow value), and % of trip downstate (basically nonstop). Something that really stood out was when plotting the actual mpg against the % the guino was high that time. To make the charts better readable I subtracted 30 from one car's mpg and 25 from the other, to keep the same data trend but to place them together.

The other things did not have near as much correlation.

So essentially the less pulse width my injectors are getting, the more the guino is off. Since the injector delay is constant, a shorter pulse width means a higher percentage of each pulse is made up of injector delay, and a lower percentage of actual fuel flow. The guino thinks I have more fuel flow at these shorter pulse widths and therefore fuel use reads high. So it sounds like I need to bump up the injector delay so it will consider less of each pulse as fuel flow and more of each pulse as injector delay. Then readjust the usec/gal because a little change in injector delay will probably make a big change in usec/gal needed. But once the injector delay is correct, that should make the rate of change correct, then the usec/gal can be set and it should be pretty linear.

I'll have to think about it for awhile, but it seems there should be a way to figure out what to set my injector delay to, in order to get things properly on track. Maybe a system of equations or something. It's been a long time since I have done that kind of thing.

Any math whizzes wanna play around with it?

Edit: The last value on the Celeb chart should be ruled out as an outlier. The tank ran out considerably sooner than it should have. I found no fuel leaks and no guino problems, so I think some of my gas got stolen.

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