Need help with understanding MAF adjustments.

[jfpilla]

Lol! that's me in all of those Joe.
Unknowns????...What are 'KNOWNS"?

I think it's as simple as your post #58.
Jetblast,

Just one point that I think needs to be plastered somewhere.

You should not and cannot tune VE's with the MAF enabled.
Sorry for yelling!

[joecar]

...

Just one point that I think needs to be plastered somewhere.

You should not and cannot tune VE's with the MAF enabled.

Yell louder.

[hymey]

I think many people do not understand the maf system in these computers. The maf is an accurate way of measuring airflow to an engine but there is nowhere in the software that allows you to tune afrs accurately at every load point.

We only see rpms as the input and hz as the output. The is no tables like we see in a Turbo Nissan where we have a proper fuel map.

That is why the maf table only takes effect after 4000rpm. The throttle butterfly will be all the way open anything above this.

Anything below 4000rpm the maf tables are useless. I can drive on the freeway at 20% throttle and 3000rpms and have low maf readings. Or I could have 80% at 3000rpms and have high maf readings.

I still dont know why GM didnt implement the MAF as the main source of fuel calibration and implenting proper fuel tables.

After all with WOT 4000rpm+ loads the pcm is still using the MAP vs rpm table for fueling calculations.

As discussed already. The only thing we can do is correct calculated frlow rate to actual flow rate.

I know the whole MAF tuning thing is bigger in the states. But speed density is more popular in Aus. I can obtain more accurate WOT fueling with sd as with MAF tuning afrs oscillate at high rpms even after the VE and MAF are both dialled in.

[redhardsupra]

MAFhz is not an output, it's about as much of an independent variable as we got.

as per SD vs MAF tuning, read this: http://redhardsupra.blogspot.com/200...ss-models.html

[dfe1]

Frankly, I think all this conversation is great mental exercise, and although it does lead to a better understanding of system functions, most of it is irrelevant. All we really care about is actual air/fuel ratio being as close to commanded as possible. If you're commanding 14.68:1 and a wide band indicates 14.68:1, what else really matters? If tuner A achieves stoichiometric bliss be altering VE and tuner B achieves it by tuning the MAF table, it really doesn't make much difference-- personal preferences aside.

As for "should not, cannot" tune VEs with the MAF enabled I have to disagree. I've found that the VE tables for MAF and SD are significantly different. Try optimizing a VE table in SD mode and switch back to MAF or vice versa and see what happens. If you tune in SD and switch to MAF, you have to make adjustments either to the VE table or the MAF table. As an experiment, I tuned a stock 5.3 in a truck by only altering the VE table until I got the long term fuel trims between 0 and -4%. So if the fuel trims are where I want them, and the wide band is telling me that what I want is what I've got, how does it get any better?

The MAF systems used from 1986 through 1989 were true MAF systems- there was no MAP sensor installed and no VE table. The 1990-93 speed systems were true speed density systems with no MAF included. The LS systems are actually hybrids that use MAF, MAP and a combination of both, depending on the operating environment.

From a theoretical viewpoint, this is certainly not the most elegant solution, but it's relatively straightforward and it works. I'm not saying this is the "be all, end all" of the subject, but I just don't see the payback in spending all kinds of time working with variables that don't seem to do much besides add complexity to a relatively simple situation. If someone has a good explanation with practical application, please post it.

[joecar]

From a practical viwpoint, if MAF is enabled, how do you determine at any instant if airmass is coming from MAF or VE (you want to know which table to apply the correction to)...?

[jfpilla]

Quote:
Originally Posted by dfe1
Frankly, I think all this conversation is great mental exercise, and although it does lead to a better understanding of system functions, most of it is irrelevant. All we really care about is actual air/fuel ratio being as close to commanded as possible. If you're commanding 14.68:1 and a wide band indicates 14.68:1, what else really matters?
xxxxxThis must be in SD, so it's fine.

If tuner A achieves stoichiometric bliss be altering VE and tuner B achieves it by tuning the MAF table,
xxxxxThe MAF does not command Stoich.

it really doesn't make much difference-- personal preferences aside.

As for "should not, cannot" tune VEs with the MAF enabled I have to disagree. I've found that the VE tables for MAF and SD are significantly different. Try optimizing a VE table in SD mode and switch back to MAF or vice versa and see what happens. If you tune in SD and switch to MAF, you have to make adjustments either to the VE table or the MAF table. As an experiment, I tuned a stock 5.3 in a truck by only altering the VE table until I got the long term fuel trims between 0 and -4%.
xxxxxNext time you do this disable the MAF and see how badly the car
runs.
-VE's have 3 functions, as far as I know, in an MAF system.
open loop startup.
-Rapid throttle transitions
-MAF failure.
xxxxxxWith your method the MAF better not fail.

So if the fuel trims are where I want them, and the wide band is telling me that what I want is what I've got, how does it get any better?

The MAF systems used from 1986 through 1989 were true MAF systems- there was no MAP sensor installed and no VE table. The 1990-93 speed systems were true speed density systems with no MAF included. The LS systems are actually hybrids that use MAF, MAP and a combination of both, depending on the operating environment.

From a theoretical viewpoint, this is certainly not the most elegant solution, but it's relatively straightforward and it works. I'm not saying this is the "be all, end all" of the subject, but I just don't see the payback in spending all kinds of time working with variables that don't seem to do much besides add complexity to a relatively simple situation. If someone has a good explanation with practical application, please post it.

xxxxxThis is the relativist approach usually argued for by tuners that won't spend the time to do it right. We have tuners that do it right on this forum. I would rather tune it the "best way" possible and avoid the learning out problem .[/quote]

[joecar]

Basically, how do you "correct" some thing based on feedback from output derived from other sources mutually orthogonal to this thing...?

[jetblast]

i've read that volumetric efficiency continues to encrease up to 20k miles and then begins to fall off, the fellows that tune in op loop first,do you take this variable into account?

[hymey]

The proper way to alter the afr for maf calculation is to dial in the VE table first and then scale the maf air flow output to suit.

I would like to see someone do this with an e38 though. With the MAF connected the afr oscillate at high rpm. You can fix this 2 ways. Fudge the maf table even more to correct the difference in fuel mixtures or go to the VE table and correct it there.

I have tuned using solely the VE table with the MAF still connected and also disconnecting the MAF and tuning the VE table first.

I said previously. The delphi computers use solely a rpm vs MAP table to control injector duty cycle. The MAF is only a patch over the top. At full throttle the MAF gives an output reading which then corresponds back to the VE table to obtain the correct figure required. SO why have it there at all.

I understand the VE table is only accurate in the weather conditions it was tuned in and that a correctly scaled MAF will correct any slight changes in air pressure and temperature due to the simple fact that air flow is a much better way of calculating and tuning for optimum conditions than Manifold air pressure.

I believe some earlier models used a MAF vs rpm table for fuel mixtures. No MAP sensor existed. Why didnt GM keep using this type of MAP. The Japanese use it religously on all there performance cars and with the 6.0L having 90mm MAF sensors it would be nice to see a table like this in the later model computers.

Some engineers I studied with a while back always believed the manifold air flow was the best data to collect for accurate fueling.

But all I see is people perservering with scaling MAF tables by a few percent here and there.

Does anyone see my point?