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Old 06-20-2008, 08:25 PM   #1
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Need OBD2 Datalog Help - Shift Point/Cruising Speed

Alrighty, new to the board. I have a datalogging system for my Ranger pickup truck that I would like to be able to use to give me some information. While I'm not the most computer/automotive guru on here, I have a decent understanding of what the values are looking at, and why they are there.

However, I am looking for my livedata datalogging to tell me the following:

Most efficient shift rpm and most efficient cruising speed/rpm.

I would have to say that SOME pids have to yield this kind of information, can anyone help? What parameters should i watch while i say, shift each gear at 2000rpm from a dead stop? then try at 2500 shift? 3000 shift? I'm looking for where my engine works less, and i know in some combinations it may be in the 2500-3000rpm range.

Thanks!
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Old 06-21-2008, 04:45 AM   #2
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You can datalog the injector pules and see what senerio give you the lowest number of injector pulses. The best would be a fuel flow meter and gps speed and then you can find Gallons per Hour to find your sweet spot (lowest GPH)for cruising.
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Old 06-21-2008, 05:46 AM   #3
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cobra marty is right. What system are you using for logging? If it's a standard OBDII logging system then it can't read fuel flow rate (though some [such as the ScanGauge II] calculate it, I think from MAF and O2 sensors).

In my sig there's a link about a DIY fuel flow rate meter that measures fuel injector duty cycle. I've been using it and found that, in my 2008 VW Rabbit with its 2.5L normally aspirated engine and 5 speed manual, there is no condition in which higher RPM is more efficient (meaning, produces the same power with less fuel) than lower RPM. It confirms what I figured based on experimentation, using different shift patterns and calculating my MPG when I fill up. If I want to run this car down to idle speed when I shift I still gain MPG (though at that point acceleration is slow).

For cruising at a specific speed, using a fuel rate meter will definitely tell you easily and immediately which gear is best.

For accelerating it's difficult because it's tough to duplicate acceleration rate with different shift points, and my meter doesn't do any logging so it's tough to add it up.
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Old 06-21-2008, 01:52 PM   #4
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Thanks for the replies, its actually the 'tuner' software my truck came with. I can datalog a few different pids with my laptop in the truck. I'll list some PIDs i think are related and see if that will help

Injector pulse width - bank1
Injector pulse width - bank2
STFT -b1/b2
LTFT - b1/b2
Load
MAF Voltage
RPM
TPS (%)
Fuel Control State
VSS
o2 - b1/s1, b1/s2, b2/s1, b2/s2


I'd think injector pulse width and vss may be what im looking for to determine cruising speed/rpm?
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Old 06-21-2008, 02:15 PM   #5
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I messed with the fuel injector PW pid, seems like it just shows a up and down scale of what its doing. It's not giving me a millisecond figure, but its showing a graph, so i figure i can head down the road at 60mph, 65mph, and 70mph and watch where the figures are.
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Old 06-21-2008, 02:59 PM   #6
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That's very cool that you can get injector pulse width from it. That's the only major data missing from standard OBDII for hypermiling usage.
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Old 06-21-2008, 04:49 PM   #7
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Thanks, so thats the parameter I should be watching. Of course as it goes up the injector is open longer = more fuel consumption. So i should pick my cruising speed by the lowest time open, correct?

Thanks for the help.
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Old 06-22-2008, 05:01 AM   #8
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No, you should pick your cruising RPM (for the same speed -- in other words, choosing a gear) based on the lowest time open. For picking your speed you need to figure in distance as well as fuel used, in other words you need MPG numbers for that.

You can determine it partially by the method used in this post:
http://www.gassavers.org/showthread.php?t=7130
I suspect that aerodynamic drag throws off those calculations, but at least it's a start.
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