Evoscan AFR formula without wideband?
Apr 30, 2010, 01:05 AM
#16
^heh. Again I say that this is not for any sort of tuning purposes. It's just a, "hey what if? Or has anyone thought of this?," not intended to start trouble. 
I only want this for my evoscanGPS logger purposes. I want to be able to get an IDEA of afr's on my specific car, without needing to plug in my LM-1.
I've been taking a lot of fluid mechanics lately, and thought there might be a way to calulate afr using the cfm or g/s or whatever coming in to calc a rough idea of what afr's might be. Q(in)=q(out), right? For heat and or other factors, I can try simple Bernoulli or pVnRT...but I don't think that is really that necessary.
I will try to sit down this weekend and get a rough formula for evoscan, in between studying for finals...
@ceddy: my injectors are scaled very well (ft's within +/- 4 year round). AFR_map does not correspond directly to AFR checked on the WB. This is due to leanspool, and a maf that is not fully scaled to my specific setup. I am fully aware of what is going on with how the ecu controls fuel. I just do this kinda nerdy stuff to expand my knowledge of random sh-t
I only want this for my evoscanGPS logger purposes. I want to be able to get an IDEA of afr's on my specific car, without needing to plug in my LM-1.
I've been taking a lot of fluid mechanics lately, and thought there might be a way to calulate afr using the cfm or g/s or whatever coming in to calc a rough idea of what afr's might be. Q(in)=q(out), right? For heat and or other factors, I can try simple Bernoulli or pVnRT...but I don't think that is really that necessary.
I will try to sit down this weekend and get a rough formula for evoscan, in between studying for finals...
@ceddy: my injectors are scaled very well (ft's within +/- 4 year round). AFR_map does not correspond directly to AFR checked on the WB. This is due to leanspool, and a maf that is not fully scaled to my specific setup. I am fully aware of what is going on with how the ecu controls fuel. I just do this kinda nerdy stuff to expand my knowledge of random sh-t
Last edited by SoCalRedLine; Apr 30, 2010 at 01:12 AM.
Apr 30, 2010, 01:25 AM
#17
In the above linked thread Jack_of_Trades, kind of put a AEM spin on the Mitsu fuel maps which isn't entirely accurate. They both do the same thing in the end, but take different approaches in the middle.
The Mitsu fuel table is a compensation. 0x80 = #128 = 100% = 14.7
The ecu kind of always calculates 1 gram fuel for 14.7 gram air and uses the fuel table to compensate for different target AFRs.
Load is actually g/rev (Grams of Air per Crank Revolution).
If you take g/rev x fuel map x constant, you have the IPW that JOT showed.
Taking Load out of the fuel map like Mitsu does has several advantages. First you have easy to read AFR scaling. Second it gets rid of the need for things like Boost Comp, its automatically done, because of how everything is calculated.
The Mitsu fuel table is a compensation. 0x80 = #128 = 100% = 14.7
The ecu kind of always calculates 1 gram fuel for 14.7 gram air and uses the fuel table to compensate for different target AFRs.
Load is actually g/rev (Grams of Air per Crank Revolution).
If you take g/rev x fuel map x constant, you have the IPW that JOT showed.
Taking Load out of the fuel map like Mitsu does has several advantages. First you have easy to read AFR scaling. Second it gets rid of the need for things like Boost Comp, its automatically done, because of how everything is calculated.
We tell the Ecu with maf scaling and maf comp what the g/rev is based on whatever maf hz its reading at the moment but it can't take into account worldly variables like the motor VE as it changes at rpm vs throttle position etc.
Apr 30, 2010, 05:23 AM
#18
That's because the settings are not correct and accurate then. The fuel table is totally ignored in closed-loop. The ECU shoots for 14.7:1, which is all it can even do with a narrow-band. Scale them to be correct in full-time open loop; it's more accurate and, IMO, easier than messing with trims.
I guess you are welcome to choose one or the other, matching open or closed loop. But, consider that closed loop operation has an extra layer of feedback from the O2 sensor that helps ensure accuracy, so it would, in theory, be a more accurate interpretation of the set values.
The point of all the sensors and all the calculations is to give the engine the right amount of fuel, so you're saying all of it is wasted because it cannot be done, is wrong, or just comes down to being an educated guess (or just a plain old guess). I guess I'd prefer to get things close instead of fudging the crap out of the fuel map to get my AFRs where I want them.
Either way, your reply still has nothing to do with my main point that monitoring AFR MAP will not reflect any issues that may arise when something goes wrong. If you lose a vacuum line on the FPR the AFR MAP would still show 11.2:1 (or whatever) when you've just lost ~20 psi of fuel pressure and are really running much leaner.
May 1, 2010, 08:09 AM
#19
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Either way, your reply still has nothing to do with my main point that monitoring AFR MAP will not reflect any issues that may arise when something goes wrong. If you lose a vacuum line on the FPR the AFR MAP would still show 11.2:1 (or whatever) when you've just lost ~20 psi of fuel pressure and are really running much leaner.
The fuel map, at the root, is a collection of values between 1 and 256 that assigns a specified amount of fuel in relation to the metered airflow
Last edited by jrohner; May 1, 2010 at 08:15 AM.
May 1, 2010, 04:21 PM
#20
My 'main point' was that you can get them to match up quite well. Obviously it won't when something goes wrong. You said before that the fuel map is IPW, which it very much is not, it's just telling the ECU how much leaner or richer than 14.7:1 you want.
Nope. 8-bit is 0 & 255, not 1 to 256. Nothing in the ECU is the actual value we use; look at timing as well, it doesn't matter -- that's what the ECU uses. I know how computers work; I'm a computer tech & I've done work in hex editors before (recently, and 10-15 years ago).
Nope. 8-bit is 0 & 255, not 1 to 256. Nothing in the ECU is the actual value we use; look at timing as well, it doesn't matter -- that's what the ECU uses. I know how computers work; I'm a computer tech & I've done work in hex editors before (recently, and 10-15 years ago).
You would need a wideband to begin tuning the Ecu in order to make the maps match up in the first place. Out of the box it certainly wont work in the way everyone i think is expecting.
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