Drastic mileage change, is it real?
10-14-2018, 11:40 AM
#1
Pro
Thread Starter
Drastic mileage change, is it real?
Did a Stage 2 cam and new Heads and mileage in the DIC has fallen from 29hwy to 16ish. Is this taken off manifold vacuum and thus probably a false reading now? Haven't taken actual mileage old school from one fill up to the next yet.
10-16-2018, 03:14 PM
#2
Instructor
It's based on how much fuel the computer thinks it's delivering. In all my experience it's been pretty accurate. Are you looking at instant MPG or average? If the car was tuned for the mods then all the WOT can drag the average down. I've never seen more than a couple mpg difference from heads/cam change on my personal cars.
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CorvetteBrent (10-23-2018)
10-17-2018, 09:44 AM
#3
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Thread Starter
It's based on how much fuel the computer thinks it's delivering. In all my experience it's been pretty accurate. Are you looking at instant MPG or average? If the car was tuned for the mods then all the WOT can drag the average down. I've never seen more than a couple mpg difference from heads/cam change on my personal cars.
If the “computer “ is looking at vacuum to determine fuel usage it may be incorrect when a different cam changes vacuum.
10-18-2018, 11:21 PM
#4
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St. Jude Donor '13-'14-'15
NO the computer is just seeing how much fuel is being used per each mile of driving---
Typically if you mileage is way off it is due to a tire size change On a C5 a rear gear change does not affect the Speedo but a tire size change will--- I see no reason for your mileage to go way south unless you changed tire sizes
PS There is an exception
Did you have your engine re -tuned after all your mods ?? This is a MUST --even if your engine appears to be running fine these major mods will affect your fuel trims at P/T and the ECM can dump large amounts of fuel into your engine because of sensor mis information
It is not uncommon wirh LT headers or a cam for the fuel trims to go way positive as much as 20% before even getting a code so at P/T the ECM adds 20% of fuel as it;s believng that the fueling is LEAN when in fact it is NOT lean at all---it just needs tuning to address the mods to eliminate the mistaken fuel addition In my experience with LT's and cams we often have to turn OFF the fuel trim corrections as they are false corrections-- due to the mods----The only true way to verify the actual fueling is with the use of a wideband---Just common sense and experience says if your milage went so south then if can be fixed with proper tuning
PS There is an exception
Did you have your engine re -tuned after all your mods ?? This is a MUST --even if your engine appears to be running fine these major mods will affect your fuel trims at P/T and the ECM can dump large amounts of fuel into your engine because of sensor mis information
It is not uncommon wirh LT headers or a cam for the fuel trims to go way positive as much as 20% before even getting a code so at P/T the ECM adds 20% of fuel as it;s believng that the fueling is LEAN when in fact it is NOT lean at all---it just needs tuning to address the mods to eliminate the mistaken fuel addition In my experience with LT's and cams we often have to turn OFF the fuel trim corrections as they are false corrections-- due to the mods----The only true way to verify the actual fueling is with the use of a wideband---Just common sense and experience says if your milage went so south then if can be fixed with proper tuning
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CorvetteBrent (10-23-2018)
10-19-2018, 10:09 AM
#5
Instructor
It doesn't care about vacuum. It only looks at the amount of fuel that is being sprayed to estimate mpg.
10-19-2018, 12:54 PM
#6
Pro
Thread Starter
NO the computer is just seeing how much fuel is being used per each mile of driving---
Typically if you mileage is way off it is due to a tire size change On a C5 a rear gear change does not affect the Speedo but a tire size change will--- I see no reason for your mileage to go way south unless you changed tire sizes
PS There is an exception
Did you have your engine re -tuned after all your mods ?? This is a MUST --even if your engine appears to be running fine these major mods will affect your fuel trims at P/T and the ECM can dump large amounts of fuel into your engine because of sensor mis information
It is not uncommon wirh LT headers or a cam for the fuel trims to go way positive as much as 20% before even getting a code so at P/T the ECM adds 20% of fuel as it;s believng that the fueling is LEAN when in fact it is NOT lean at all---it just needs tuning to address the mods to eliminate the mistaken fuel addition In my experience with LT's and cams we often have to turn OFF the fuel trim corrections as they are false corrections-- due to the mods----The only true way to verify the actual fueling is with the use of a wideband---Just common sense and experience says if your milage went so south then if can be fixed with proper tuning
PS There is an exception
Did you have your engine re -tuned after all your mods ?? This is a MUST --even if your engine appears to be running fine these major mods will affect your fuel trims at P/T and the ECM can dump large amounts of fuel into your engine because of sensor mis information
It is not uncommon wirh LT headers or a cam for the fuel trims to go way positive as much as 20% before even getting a code so at P/T the ECM adds 20% of fuel as it;s believng that the fueling is LEAN when in fact it is NOT lean at all---it just needs tuning to address the mods to eliminate the mistaken fuel addition In my experience with LT's and cams we often have to turn OFF the fuel trim corrections as they are false corrections-- due to the mods----The only true way to verify the actual fueling is with the use of a wideband---Just common sense and experience says if your milage went so south then if can be fixed with proper tuning
Maybe I’m missing something but where does the computer measure fuel consumption that exact? When you change injectors it can’t go on injector pulse width anymore. Or can it? I get your saying it measures fuel consumption but exactly how?
Thanks for the help,
Randy
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CorvetteBrent (10-23-2018)
10-22-2018, 09:51 AM
#7
Instructor
Livernois Motorsports did my Heads and cam and new tune. I can get back with them but I was just wondering if the reading was false. I filled up yesterday and will check old school mileage next time I fill.
Maybe I’m missing something but where does the computer measure fuel consumption that exact? When you change injectors it can’t go on injector pulse width anymore. Or can it? I get your saying it measures fuel consumption but exactly how?
Thanks for the help,
Randy
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CorvetteBrent (10-23-2018)
10-23-2018, 03:58 AM
#8
Pro
Thread Starter
[QUOTE=nickalltogether;1598201878]Pulse width changes, but there is also a table that is re-calibrated for higher flowing injectors. So in a basic sense, it knows how much the injector flows per unit of time open, and it knows how long it commanded the injector to be open.[/QUOTE
Thanks, that makes sense.
Thanks, that makes sense.