Grumpy

OK, so what's this MAF stuff anyway?.

It's just a way of calculating how much the air the engine is using, and when you compare that to RPM, you can figure out how much load the engine is under. once you know the load, then you have an idea of the desired AFR, then you can figure Pulse Width.

Easy right?.
Well, no.

The ecm has it's faults, it's bliind as a bat, and dumb as a rock. But it can do math really fast. LOL

Since I just finished a few million hours of MAF tuning on my GN, I'll talk in GN terms. The GN MAF is a frequency based system so whenever I use frequency, you think of the MAFs output voltage.

This is kind of backwards and upside down, but it's the only easy way to explain it, that I know of.

This also is based on using a LT1 MAF housing with a LS1 sensor and removing the screen, and vane. So the MAF has been seriously reworked, and the recal is necessary.

First I went thru and with an almost stock MAF dialed things in so that I had 129s about everywhere. That way I had a known baseline.

I then installed the modified sensor.

And immediately saw that HOUSTON'S, MISSION CONTROL, had some problems. BLs at idle were in the 90s, and WOT went WAY RICH.

I've drawn the following conclusions (right or wrong, they are my conclusions).

In order for me to understand the range of each table, I use the scaler entry as being the gm/sec limit of that table, when the last entry is 255.

If table one has a scaler of 10.
and the 9th entry is 255, that would mean the table goes from min air flow to 10 gm/sec. The math is entry * table value, divided by 256 at any given point would represent gm/sec..

So if you used 4 as a scaler the whole table would max out at 4/gms sec., and slide into the 2nd table.

So you also need the second table to line up with the first.

So if you want the second table to start at 10 gm/sec and end at 40. You would use a scaler of 40, the last entry would be 255, and the first entry would be 10 times 255, divided by 256, and that diveded by the new scaler of 40 or, a first entry of 61. The you would have to drive the car to see how the other table entries line up, becuase you'll have all kinds of hills and vallies from non laminar airflow, and reversion.

Once you figure things out, and see what your car likes, figure on 100 or so chips to get it close. This is really time intensive.

NOW, if you sit and study this a while you'll see why MAF is so FORGIVING. And the clue is that it isn't, it just is a very coarse way of reading load so with this low of resolution of tables, it's forgiving, is all. When you plot the voltage vs air flow numbers out you'll see how the WOT stuff gets all crunched up in the last table. They overcome this with the PE vs ROM, and PE vs TPS stuff.

Now, as a matter of example,
my car is idling at 4 gm/sec, per calculations the ecm is making, and WOT is only 160 gm/sec. But, remember these are just numbers the ecm is using now, since the MAF has been recalibrated.

Now, if you look here, you'll see how this mounting has developed a small expansion chamber, so that might explain the weirdness in the calculated airflows. But, that is meaningless, as what does matter is the AFR at that the new MAF values is correct. Which just leaves changing all the other LV8 stuff to match now..........

http://www.gnttype.org/techarea/engine/mafrelocate.html

Later,
Bruce

Grim Reaper

This deserves to be sticky.

quickL98

iTrader: (2)

hey!?!.... when did this site display stuff in german

give me a week and i'll be at work oneday welding a 1/4 panel and suddenly say OHHHHH i get it:lala:

kvu

So I guess this means I can use a digital maf w/ my third genner?Oh yeah, just get a maf connector for a gn and splice the existing maf wiring to it.Then use the translator and the digital maf.It's my bright idea,would it work?

Grumpy

Ugh, No.
Haven't you been following the other threads where the interface is being talked about?. This thread is about the recalculating the MAF, a seperate issue from the interface. As stated you bright idea won't work. You need to go from Freq to voltage on the MAPs output.

doc

Grumpy,

I've been away from this site for more than a year, with only a few visits to try to keep up with whats going on. I,ve been modifing and PCM tuning my '99 Camaro SS. Its now at 400Hp at the drive wheels normally aspirated.

Anyway, to my point.

When I was burning Eproms for my 87 IROCZ, I held the believe that the MAF table was not to be messed with. However, with my '99 car, I realized that the best way to get the long term fuel trims (BLMs here) under control and near 0% (BLM=128) that I had to calibrate the aftermarket MAF that I installed. It was obvious to me that the factory PCM MAF table relating frequency to air flow was way out of calibration. I spent an entire month getting the LTFTs under 0%. (With LTFTs under 0%, the PCM will not take fuel away or add fuel doing WOT.)

I had a choice to make, I could alter the fuel injector flow constant or I could alter the MAF table. Because I am running the stock fuel system and using a non-factory MAF (GMAF), it was obvious to me that I should change the MAF table.

So I am rethinking my tuning stuff on my '87 car. Since I have modified the factory MAF and change fuel injectors, I should set the fuel injector constant to what I calculate it to be, and recalibrate the MAF table so that I attain 128 for the BLMs.
By adjusting the fuel injector constant only, my cause other tuning problems such as at WOT.

What are your thoughts on this matter? Of course, I welcome all thirdgenners to comment.

Grumpy

If you want to get the car happy, and running great, it's really simple.

Set the injector constant for what the actual injectors your running.
Get a WB.
Set the chip to stay Open Loop.

Diddle with the MAT tables till you get the AFRs you want. The Stoic stuff is nonsense.

http://www.gnttype.org/techarea/chips/chiptips.html

Here's my latest MAF stuff.

doc

So what do you do if you dont want to spend $1000 on a WB?

Or maybe I should ask what does a WB cost these days????

I know what you are saying about using a WB. I agree, I just dont want to spend money on one. But I wish that I had one.

I looked over your link above, really good stuff, I'm impressed.

I developed a tuning technique on my LS1 car, whereby I re-calibrated the MAF table (which is frequency vs air flow) based on the value of the LTFTs. This same technique will work on my '87 given enough burning of chips. Yes, it is time consuming.

Grumpy

Build one yourself.
DIY-WB.COM
Maybe have to learn to solder and do electrical stuff but for under 200 and using a meter you could have one, or 250 with a GOOD LED Display.

And that 200 is figuring screwing up 2 of the printed circuit boards learning how to solder.

D's89IROCZ

129 Baseline .....as opposed to what ( real newbie here) . BL????? and what is considered a rich condition ( ie what table and what is the value )

thanx alot
Dan

blue86iroc

iTrader: (2)

The math doesn't quite work out for me...

"entry * table value, divided by 256" and "first entry would be 10 times 255, divided by 256, and that diveded by the new scaler of 40 or, a first entry of 61"

I've been experimenting with using proportions, and it seems to work. With regard to your example on carrying over to the second table, I just set 40/255 equal to 10/x, to give me the value for 10 gm/sec if the scalar is 40. However, I got 63.75, which isn't quite as close as your value of 61.

Am I interpreting this incorrectly?

87400tpi

how can I appy this data to my third gen firebird?

funstick

scalar= maf table maximum value in grm/sec. table value divided by 256 x scalar euqlas table entry value. for exapmle!


scalar is 120

counts ---table value-------------grams/second
1------------20----------- 20/256 x120=9.375
2------------30-----------30/256 x 120= 14.0625
3------------40-----------40/256 x 120= 18.75
4------------50-----------50/256 x 120= 23.75
5------------255--------255/256 x 120 = 119.256
so on and so forth now watch this equation folks heres the mathmatical limit.

255/256 x 255 = 254.0000039etc etc etc ahhhh

Hooter

Hi Doc, Like you I get busy and dont visit too often.......
In reply to your post, the factory have added a map to the late Air Frequency Meter programs for cylinder correction.
How you guys manage (timewise) to map all these earlier programs beats me. What we have done is copy this Cylinder correction map to the earlier programs. We have added it to the 165, 730 & 278 ecm, as well as a couple of the Australian ones.
So typically when tuning, i hold rpm at say 2000 or 2400rpm at say 300gms and adjust Injector Rate until I get 128 on STFT with BLM turned off and cleared. This is with the Cyl correction at factor of 1.
I usually use WB as a secondary tool at this stage.
From here I then adjust the Cylinder correction (this is a 3D map) and usually the correction below this point is less than 1 (ramps from approx .875 up to approx 1.1 above the 450gms table.
Also usually you can look at say the 250 gms in X-axis and it will nearly always be the same figure throughout the rpm range, and similarly up at say 500gms it will be say 1.085 through the complete x axis.
I usually back off the PE so that it stays at 14.7 under load at higher rpm temporarily, so that I can get cylinder correction close, then I use the wide band to get my PE correct.
Also the factory have a tendency to set PE TPS threshold quite high,(often over 60%) whereas in the Buick SC3800, PE cuts in at 40% TPS.
This makes a hell of a difference to throttle response.
Some may argue this is for economy, but I believe, if you give it what it wants, you dont have to give it as much pedal......
On a MAP (speed density) engine you often see 100kpa with only 40% TPS which gives approx A/F of 13:1, so what the hell.
Obviously using realtime software allows us to do this, and makes it very easy and quick, even with big cams, also we use the different factory AFM sizes 67ml, 76ml and 85ml, and also borrow the extended calibration tables from Corvette and Buick to suit these meters.
We love them and get very accurate 128 STFT (short term fuel trim) direct from front narrow band o2 sensor, as this is what the ecm wants to see, rather than tuning to WB. We do not touch the AFM tables.
Air frequency meters work beaut on multi throttle body setups, where, because of having such high cfm passing thru' throttle blades at low TPS at lower rpm, you can end up with 100kpa at as little as 10%TPS when using MAP sensor which gives you no resolution, whereas with AFM it measures air consumption, which cleans it right up.
I wish I had access to a GN, we dont get them here, I've had a look at your GN threads Bruce, looks interesting...
We have a SC3800 here that we have just taken off a 14psi Vortech and replaced with big turbo. At present we are running a 76ml GEN 3 AFM which is right on the limit of maxxing out.

Anyway, hope you find this of interest.
Hooter