05-18-2015, 03:56 PM | #15 |
Drives: 2014 1LS Join Date: May 2014
Location: Hot Springs, AR
Posts: 76
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I thought the system increments a running total of the amount of time the fuel injectors have been commanded open to measure the fuel used. It ought to be pretty accurate given the precision of the injectors. I don't think there is any estimation involved.
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05-18-2015, 04:41 PM | #16 | |
Drives: 2010 RY 2SS/RS Join Date: Dec 2007
Location: Miami
Posts: 817
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To the OP, I have no clue if it is an estimate or what, I always figured that the computer could measure what comes out of the injectors (or fuel pump) and calculate against distance traveled. Either way there can still be error in the measurement of fuel or estimation. I have tried to do this same tracking but didn't care enough to follow through. When I did it my calculated miles tended to me 1-3% better than the DIC. I figure there could easily be enough variation between how "full" I filled the tank to account for the difference between 1% and 3% as this is basically 1/3 of a gallon. I just assumed the average over time was about right.
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05-18-2015, 05:41 PM | #17 |
the computer knows without a shadow of a doubt how long it has pulsed each injector since the last time you reset the average MPG entry.
it also knows without a doubt the wheel spin count. now, you have to trust in the GM engineering crew to model the injector performance accurately (fuel flow vs pulse width), and the diamter of the wheels to be accurate. the value used for miles traveled is the same for your spreadsheet as it is for the ECU. all of the variance lies between injector modeling and how consistent you can fill the vehicle each time. does it always auto-shut-off at exactly 18 gallons? probably not. this fill-up's slight overfill is your next fill-up's improved mileage. I'd trust GM's injector modeling over a number of different fuel pumps' auto-shut-off consistency. |
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05-18-2015, 07:42 PM | #18 |
Drives: 2014 Camaro 2LS Join Date: Oct 2014
Location: New York
Posts: 167
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I did think of that. How full is full, either being done at the first stop, and topping it off. But overall the variation should go to 0. (limits, I do teach calc lol)
And dont joke about that. I nearly lost it when the dealership (with my Crown Vic) had my car for 8 weeks and they added a gallon at a time, and messed up that and the next calculation. Of course that paled compared to when I found out why my car was in that long, that they dropped it off a lift. And I keep records of every maintenance action, like "Engine whining under load" and corrective action "Could not duplicate" Actually writeups like that help a LOT long term if something does got wrong. You can spot when something may have happened and maybe trigger the cause. Less important now when the cars are new, but 10 years from now, big help
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2014 Chevy Camaro 2LS
2004 Crown Vic Sport (my first new car) 1973 Lincoln Continental Town Car "Black Jack" 1972 Lincoln Continental fully original down to paint |
05-18-2015, 07:46 PM | #19 | |
Drives: 2014 Camaro 2LS Join Date: Oct 2014
Location: New York
Posts: 167
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The Camaro being on the right, and me having my injury means Ive gotten lazy, although if I see one more dumb clerk just let the cap dangle against the quarter panel, Im just going to have to put a locking cap so I have to get out and do it myself
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2014 Chevy Camaro 2LS
2004 Crown Vic Sport (my first new car) 1973 Lincoln Continental Town Car "Black Jack" 1972 Lincoln Continental fully original down to paint |
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05-18-2015, 07:46 PM | #20 |
Drives: 2011 IOM 2SS/RS M6 Convertible Join Date: Feb 2014
Location: Southern Illinois
Posts: 1,287
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Sure, but how would you know what the last guy did? lol
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05-18-2015, 08:11 PM | #21 | |
Buick 455 Fan
Drives: 1970 Buick, 2012 1SS LS3 Join Date: Jun 2010
Location: Boston MA
Posts: 5,957
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What I'd like to know is just how the rated MPG is determined for 'city' driving: how many stops and for how long, for any period of time. Way too subjective for my taste. I can drive through Boston at 4 am and get 17 mpg, and then at 4 pm on the same route, get 8 mpg.
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05-18-2015, 08:15 PM | #22 |
Drives: 2014 2SS RS 1LE Join Date: Mar 2015
Location: St Petersburg, Fl
Posts: 372
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I think variance is more likely that your car is sitting at different angles when filling it up. Even if you fill the neck all the way to the top if you're on some type of incline in any direction yaw, pitch, or roll you're gonna have a bubble of air in the tank somewhere. If you're within 5% I'd say the computers doing a pretty darn good job. Even with your highest variance you're still less than 3/4 of a gallon different.
(edit) Actually the way you calculate it would account for any of those types of variances because of the total amount added. Either way, I still still the difference in the real time tracking and your calculations are pretty close and well within my acceptable tolerances. Then again, I never take it easy on the gas and really don't care lol |
05-18-2015, 11:11 PM | #23 | |
"Catharine"
Drives: '11 2SS/RS LS-3 IOM/IO vert Join Date: Mar 2011
Location: Southern NH
Posts: 2,132
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Quote:
Also, don't really care about mileage too much but being an anal retentive engineer type with OCD, always want to know exactly what my car is doing!
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05-19-2015, 06:03 AM | #24 |
Drives: The red one Join Date: Jan 2015
Location: Henderson, NV
Posts: 317
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The MPG readings I get on my 2015 V6 have always been within .1 or .2 of my manual calculations. That's pretty darn close. I spot check it manually once in a while but don't really obsess over it. The car only has 1600 miles on it and the MPG are slowly getting better. I typically get 275 to 310 miles per tank doing mostly suburban driving and only use about 1/2 tank a week. I really need to get it out on the highway a little more.
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05-19-2015, 07:06 AM | #25 |
Drives: 2014 Camaro 2LS Join Date: Oct 2014
Location: New York
Posts: 167
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I dont obsess over it (i compulse over it?). I just like knowing these little things about my cars, and this is a peculiarity mostly because none of my other cars have sophiticated computers.
My previous newer car still had analog odometer.
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2014 Chevy Camaro 2LS
2004 Crown Vic Sport (my first new car) 1973 Lincoln Continental Town Car "Black Jack" 1972 Lincoln Continental fully original down to paint |
05-19-2015, 09:24 AM | #26 |
Drives: 2011 1LT Join Date: Mar 2012
Location: Crestline, CA
Posts: 3,029
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Castrosua, I'm not QUITE as bad as you are, but on the same end of the sorta OCD spectrum regarding mileage calculation. I find my onboard calculator to be within 2% - 3% of actual, and it swings up or down, averaging (long- term) pretty close to accurate.
I'd love to know HOW the car calculates it, though: Does it actually measure fuel flowing through the lines? Does it estimate based upon throttle positions, angles of ascent/ descent, GPS data? Does it weight the fuel tank and compare it to miles driven? Last edited by Scalded Dog; 05-19-2015 at 09:38 AM. |
05-19-2015, 12:41 PM | #27 | |
Drives: 2014 Camaro 2LS Join Date: Oct 2014
Location: New York
Posts: 167
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Is it milieage from the computer, with I think might be GPS based too. I was looking at my odometer since I like to see with my own eyes rollovers (espcially those 100k ones that go back to 00000) but i was at 11999 then within 2 tenths of a mile I went to 12001.
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2014 Chevy Camaro 2LS
2004 Crown Vic Sport (my first new car) 1973 Lincoln Continental Town Car "Black Jack" 1972 Lincoln Continental fully original down to paint |
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05-19-2015, 02:28 PM | #28 | |
Drives: 2014 Convertible LS3 Join Date: Apr 2015
Location: Woodside, NY
Posts: 41
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But this was all over 20 years ago (with Bosch systems) who knows what they are doing now. YMMV |
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