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AFR Table Fuel Calc Usage ? (SOLVED)
Posted: Sun Mar 22, 2009 1:55 pm
by 65looter
In
http://www.megamanual.com/mt28.htm#so
AFR Table Fuel Calc Usage: The default (Use Combined AFR/VE table) calculates the fueling based on the VE table (and MAP, IAT, etc.). The AFR table in that case is used ONLY for EGO feedback control. However, by selecting the 'Separate AFR/VE table', you can have the fuel equation multiplied by the AFR table entry divided by the stoichiometric AFR, meaning the AFR is always in the calculations. In the default case, AFR and VE are really combined into the VE table, while in the other cases they are separate. Either will allow you to control a wideband EGO sensor, but the difference is that while the first relies on EGO feedback to reach the target AFR in the AFR table, the 'Separate' options do not relay on the wideband feedback, instead the target AFR are fed directly into the fuelling equation. With the separate tables, IF the VE table is correct, then changing the AFR table to another target should result in that AFR, even without EGO feedback control.
Now which one is best to use? combined or separate?
Re: AFR Table Fuel Calc Usage ?
Posted: Mon Mar 23, 2009 9:36 am
by grippo
You will get many answers for this, that is why there is a choice. But in my opinion the easiest to use for a beginner is the single VE table with no ego closed loop. Tune that VE for each rpm and map point according to what you want where you want: generally that will be what gives you 14.7 AFR under warmed up, steady state conditions, except for WOT where you can use a dyno or dragstrip to get the VE that gives you your best performance. Then you record the AFR at those points and put it in your AFR table. There is a logical progression to all this and it is given in detail in the megamanual.
Many professional tuners prefer separate VE and AFR tables, because they have the equipment to measure VE, which requires an air flow meter, and an accurate, calibrated wideband which gives AFR. So they can separate out the two.
Re: AFR Table Fuel Calc Usage ?
Posted: Mon Mar 23, 2009 11:41 am
by 65looter
grippo wrote:But in my opinion the easiest to use for a beginner is the single VE table with no ego closed loop.
Forgive me if I say something stupid there ...
So that would be the '
Separate AFR/VE table'
grippo wrote:
Tune that VE for each rpm and map point according to what you want where you want: generally that will be what gives you 14.7 AFR under warmed up, steady state conditions, except for WOT where you can use a dyno or dragstrip to get the VE that gives you your best performance. Then you record the AFR at those points and put it in your AFR table.
You kind of lost me on that one
grippo wrote:
There is a logical progression to all this and it is given in detail in the megamanual.
I'm going back to read the manual...
Re: AFR Table Fuel Calc Usage ?
Posted: Tue Mar 24, 2009 4:25 am
by grippo
You want to use the combined table - that is, afr is part of ve. I think this is the first option.
What I mean about tuning is that no one knows their ve and afr is something you can change up to a point to achieve your goal. If it is to save gas, then you make afr as lean as will give decent driving by your standards. If you want a clean environment use 14.7; if you want power everywhere, then find the afrs that give you max power everywhere and put them in the table. The purpose of the afr table is to allow you to run ego closed loop so that if injectors get clogged, gas is bad, etc, you can still get the same afr that worked when you first tuned the car. ego closed loop uses the afr table and adjusts the fuel to make the ego sensor value equal the table value.
Re: AFR Table Fuel Calc Usage ?
Posted: Tue Mar 24, 2009 6:17 am
by 65looter
Thanks a lot, I got it now
Re: AFR Table Fuel Calc Usage ? (SOLVED)
Posted: Sat Nov 28, 2009 10:21 pm
by CSM
I know this post is old...but I have a question.
When you use the 'Generate VE Table' Function, I assume it does this targeting a 14.7:1 AFR at every location in the table. My question is, if you do not use EGO feedback, is there still a way to use the AFR table to perform a simple open loop modification to the 14.7:1 afr by, say, taking the value from the AFR table and dividing it by 14.7 to use as a factor to adjust the stoic VE value at a given MAP and rpm, in order to make the mix more rich/lean? I could see how this could be of little effect, as the VE table generator can be inaccurate and a simple adjustment factor would rarely do what you intended it to, or so I would imagine. Is it just easier to play with VE values until you get the AFR you're looking for at a certian load and rpm? Thanks.