JakeFusion

iTrader: (7)

So, I'm wanting to touch up my VE table as I see my trims are a bit off... But I don't necessarily want to disable my MAF (I keep two base tunes - full MAF/VE and SD). But I'd like to just maintain the MAF/VE blended tune and tune the transients.

Can I do that? Like, if I'm logging lambda and I'm seeing .97 on a run from 2200 to 3800 or something with transient fueling, can I just take out 3% fuel in the VE table where the histogram/channel history shows I went rich even if the MAF is being used?

Typically when I tune VE, it's with the MAF off. But it seems like if I want to run them both, it'd be better to dial-in VE on the street with MAF enabled to clean up any little rough areas.

Am I right to think that? Or should I disable the MAF and keep tinkering with the VE table?

dw456post

Here is my opinion. I would fail the MAF, turn off LTFT's and tune with STFT's in the low rpm area while in closed loop. Don't need the wideband at this point. You know the other stuff that screws with fueling DFCO,COT--off.
If you get everything nice and tuned, you will leave the maf off.

MontecarloDrag

iTrader: (3)

Disable the MAF and all adders, then tune the VE table up to 4,000 RPM
Tune in MAF only mode
Enable both and that's it.

You can't tune either without disabling the other, you'll end chasing your tail.

JakeFusion

iTrader: (7)

That's what I figured.

I have tuned both. Multiple times over the last 2 years. Was looking to be lazy.

Firebirdmuscle

iTrader: (16)

When y'all tune in speed density mode for the ve table, do y'all put 0 on the steady state Hi/Lo Rpm Thresh under airflow>dynamic?

I seen in a tuning guide to do this, and have a few times but see no difference tuning ve or MAF with this set to 0 or stock settings.

gametech

iTrader: (1)

Once you disable the MAF, the steady state qualifications are no longer used, as they require MAF input.

Firebirdmuscle

iTrader: (16)

Okay. Thanks for the reply. So what about tuning MAF then, do you zero it then?

JakeFusion

iTrader: (7)

Yeah. I usually set to 400 or something pretty low so it uses MAF only when driving.

But you don't have to mess with it with SD mode.

gametech

iTrader: (1)

The only simple way to kill VE input is with the rpm table, as you have surmised. However, you need to be sure of your reasons for tuning a MAF. In stock plumbing, it is a calibrated sensor, and should be treated as such. In non-stock plumbing, toss that last comment out the window. Even so, you need to verify fuel pressure and injector data before you start screwing with airflow calculations. There is just as good chance of fuel error as airflow. This being said, the best way to do MAF tuning is to nail down the VE table with the MAF disabled. This leaves the MAF as the only remaining error in your dynamic airflow calculation. My reasoning for saying this is the almost impossibility of just disabling the VE table for MAF tuning.

gametech

iTrader: (1)

Wow. It's been so long since I've messed with a screened MAF in a stock location that I don't even grasp the concept of them being steady enough to tune with at airflows that low. Sometimes I forget that they do have their uses.

JakeFusion

iTrader: (7)

Surprisingly, the LS3 MAF does well at idle and low speed for me.

gametech

iTrader: (1)

I haven't tuned anything more recent than LS2 stuff, and that was limited. The most recent thing I have messed with is a c6z06, and that was just running the dyno and giving the my buddy hints about how to explain to his wife that he needed to turbo it.

JakeFusion

iTrader: (7)

Lol.

Well the LS3/7 MAF was giving people fits at first. But then a honeycomb straightened out airflow and boom.

But you do have to tune the transfer table with it to setup the airflow properly. As long as your injector data is good, you can tune it and tweak it to provide proper fueling. In MAF-only the car runs awesome OL and CL.

jaydubb

^^^This...

FlorianGee

iTrader: (1)

Sorry for hijacking, but I've been thinking a lot about this and did not come to a reasonable conclusion yet. First of all: what is "non-stock plumbing" to you? A different air filter? Smooth bellow? Lid? Descreened but stock MAF? Aftermarket intake?

As far as I understand, the MAF is a calibrated device that measures the airmass which passes through it in a defined period of time. For that period it spits out a Hz reading which is the translated by the PCM to g/s. I assume GM did a good job to calculate the correct g/s for each Hz reading. Why would you need to change that, if nothing physical changes with the MAF sensor itself, e.g. porting it? Because only then would you change the physical environment in which the calibrated sensor actually measures the airmass. But if you only change things that are in front or behind the sensor, you are only changing the amount of air that can pass through it but not the means to measure it. And in my mind this does not justify to alter the Hz -> g/s tables in the PCM. Or am I overlooking something important?

gametech

iTrader: (1)

Only a tiny wire in the MAF actually measure airflow. This means any disturbance that makes the air flow through the MAF differently than it did in the calibrated configuration could lead to slightly different flow across that one tiny section of the MAF that does the measuring. This is generally less of a problem as airflow goes up, but at low flow amounts, the flow is not necessarily uniform through the entire area of the MAF. This is the reason for the honeycomb screen in some factory MAFs, and the reason there are usually no bends just before or after the MAF. To answer your question, while you are not changing the amount of air flowing through the entire MAF, you may change the amount seen by that tiny wire.

mrvedit

As gametech says, the MAF is only measuring the airflow through a small portion of the intake tube. The airflow through the tube may not be completely uniform, due to any turns in it and other "minor" factors.
So, while you are correct in theory, in practice changes will skew the MAF reading. Minor things like a different air filter and a basic lid won't make much difference and the fuel trims can easily compensate for it. Descreening might skew it quite a bit.
And if you increase the size of the intake tube in which the MAF sits, the calibration will be way off.

Thanks for asking as I'm sure many people are wondering about this too.

FlorianGee

iTrader: (1)

Appreciate your answers, now all the MAF voodoo makes a little bit more sense. I wasn't really aware of the fact that only the little central part actually does the measuring.

My MAF is already descreened, now I'm thinking about putting a honeycomb screen in front of it to straighten out the airflow. Not a descreen, but a rescreen What do you think? In my case except for a different lid, a K&N filter and a smooth bellow, the WS6 inlet side in front of the MAF is stock.

But what about the portion behind the MAF? Does that make any difference in terms of skewing the MAF? For example if I install a FAST 102 to replace the LS6 intake, does this skew the MAF too? If so, why?

JakeFusion

iTrader: (7)

I have said this before, but the transfer function is what you tune in the MAF. I try to keep everything under 3000hz together. That is, if I need to add 5-8% fuel at idle or take it away, I do it for the whole of the curve.

Same goes above 3000. If I log and there's a need to add 4% in a lot of places 5% in a few 2% in a couple and so forth, I'd just go ahead and make a call of 4% across the curve. Being off 2% or so is easily controlled by the trims. But I try to move the transfer function in a uniform direction.

I use an LS3 MAF in a 100mm housing... so I started with the Lingenfelter data and moved it like I said in chunks above and below 3000hz until I was hitting my desired A/F ratio. The curve of the transfer matters... so I try to maintain it best I can. Otherwise if you just listen to what the wideband is telling you, it ends up a little wavy.