Simple MAF airflow vs. Freq table question

[Firebirdjones]

Please correct me if I am wrong. After alot of reading about this table,,,I gather I need to reset the fuel trims and drive the car and see where the average LTFT values are at.

If for example I find my LTFT average around 8 then the PCM is adding 8 percent more fuel,,,so I need to scale the entire MAF table by 1.08.

Does this mean "Multiply" the entire MAF airflow scale by 1.08?

If so this actually raises the MAF table number,,,which in turn will add 8% more fuel and then should put my LTFT closer to 0?

Do I understand this right? This should help idle and part throttle driving as long as I am not in PE mode,,,,correct?

[alanderson1978]

My knowledge of MAF tuning is limited, but I have done it once or twice.
Simplest way is to make a histogram using the table 'MAF Airflow vs. Output Frequency', then plot the LTFT PID in that histogram. It's pretty much like VE tuning, just with different axes. It would be a lot faster to disable LTFT and just use STFT. LTFT take a lot longer (50 min. I think) to settle in than STFT (10 min. I think)

I'm sure a Guru can give a much better (or correct) description.

[Firebirdjones]

I have looked at the histograms as you suggest, and how they fill in as you drive. My next question would be,,,,how do I average a single number to adjust the MAF tables with from the many various numbers that seem to range from +3 to +10 depending on rpm. It seems if I pick a single number like for instance,,,,,6,,,,,and I use that to adjust the MAF it won't make that entire histogram happy,,,then some numbers will be -3 and others +4.
Is this what I should expect or am I doing this wrong.

Also could you tell me what PID stands for? Sorry,,,don't have a grasp on all the abreviations yet

[Frost]

There is no one number for the whole table, there is one correction number per cell. PID is a control scheme. Instead of logging an actual sensor, we are logging the process variable/control output portion of the PID control. A LTFT is a good example of a control output and the O2s are the process variable that they are trying to control.

[Firebirdjones]

Sorry frost, what you said sounds like Japanese to me,,,lol.
If there is no one number for the Histo table,,,then how do I average the LTFT or the STFT's for a specific number to change the MAF tables with?

[Firebirdjones]

Can I just use the LTFT number that is on the gauge screen? When it goes to it's highest point for each bank? It simply shows = or - numbers for each side,,,seems much simpler. Bad idea?

[alanderson1978]

Take a look at the MAF Airflow vs. Output Frequency table. You need to adjust each cell of it individually. For example, 3000Hz on my truck equates to 8.06 g/sec. If my histogram showed a fuel trim (LTFT, STFT, or the sum of both) that was positive in that cell, The PCM would be adding extra fuel when the MAF output is 3000Hz. So I would raise the value in that cell.Each cell of that table will have a different value. I don't think you can copy-paste special like you can with VE, but just take small steps.
New to tuning? Step inside
This sticky in the Getting Started section explains a lot and links to several other help files.

[Firebirdjones]

Ya I have read all that but can't make much sense of it. It briefly touches on it but really doesn't go into great detail,,,,what would really help me is to have pictures of the graphs he is talking about changing along with the descriptions and explainations.
Just writing some words down (most of which are abreviated) is like reading japanese to me. I know what LTFT and STFT is but in that description he has STIT and LTIT, what that hell is that? Never seen anything with an I in it.
I think pictures help more than anything,,,especially for a new guy that is trying to understand. I am going to struggle with this for a while until I find someone local I guess that cares enough to sit down and show me some things.

[Firebirdjones]

I went to the local book store trying to find something on GM. No luck. I found many "how to tune" books on ford fuel injection and chrysler fuel injection and even on foreign cars,,,but nothing on GM. What gives?
I guess I need to search somewhere on the internet for an in depth tuning book?
Any chance of HPtuner coming out with a "How to" book? Larry.

[Firebirdjones]

Does anyone care to post pictures of graphs to help explain what some of you guys are talking about? It would be much appreciated and helps coomputer dummy's like me out tremendously.

[alanderson1978]

I looked back at what I did when I was MAF tuning, and I made a Flash animation showing what I did. I can't upload it here or Photobucket and I don't have a web page to upload to either. Get a hold of me if you want any other help.

[5_Liter_Eater]

If you set up a histogram to plot the LTFT (or disable LTFT and plot STFT) against the MAF Airflow VS: Output frequency you can see your fuel trims in relation to the corresponding frequencies and copy and paste (multiply by %) right into the appropriate cells in MAF table.

This histogram is missing from the default config.

The thing is that you will never be able to tune your upper frequencies because when you go into PE your fuel trims lock out (hopefully at zero). So you can only tune the lower parts of the MAF table where you are in closed loop.

EDIT: I attached the histograms I pilfered from EC a while back. Just import them.

[Firebirdjones]

Hmmm, if fuel trims are a closed loop function,,,and wide open throttle tuning is open loop,,,then why does + fuel trim affect wide open throttle A/F tuning?

I have read in here several times that the fuel trims need to be reading negative before any wide open throttle A/F tuning can be done because it skews the A/F ratio numbers. Is this correct?

So I am thinking I need to add some fuel to the MAF table in order to get the fuel trims slightly negative so that when wide open throttle A/F is done it won't be affected by the fuel trims. Correct? Maybe I am way off base here.

I am still trying to figure out datalogging though,,,I can record and go for a drive, save the log and give it a name,,,,I can pull it up and it shows the saved log on the screen but I can't figure out how to get it to play I am still missing something that I can't figure out or I missed it when reading on here. Larry.

[5_Liter_Eater]

Correct, fuel trims are closed loop. The problem is that if you leave closed loop from a cell that has a positive fuel trim, that fuel trim gets locked in and added to your PE ratio. So if you are +7 LTFT in the cell right before you enter PE and you're commanding 13:1 in PE you will end up with 12.15:1 (13/1.07). If you enter PE from a cell that has a negative LTFT the LTFT locks in at zero for the duration of that PE run and you command just what you have your PE set to.

You're correct, you need to use the histogram and add the appropriate amount to the appropriate cells in the MAF table to bring your fuel trims down.

You just need to click the green play button at the top to see the data populate in the charts and histograms but for the sake of getting the MAF dialed in you'll want to right click on a histogram and click 'load all data'. That way all the data for the run is populated and averaged.

[Firebirdjones]

Thanks a ton,,,that clears up some things. I wasn't too sure on my thinking and just needed to hear it from someone.

I found the tiny green play button,,,lol. works fine now.

I will have to try another log with the histogram you suggested,,,I just have to figure out how to do that exactly. I don't fully understand the purpose of the histograms yet or how they work, math formulas, and how changing blocks in there affect fuel plus or minus etc....
Thanks for the help,,,I actually feel like I made some progress today for a change Larry.

[5_Liter_Eater]

Once you harness the power of the histograms your tuning ability increases exponentially. If you import the histogram(s) you should be able to open your existing log and view it. All the parameters you need are already captured in the log (LTFT, STFT, MAF Freq). Once you do that you will see the % trims displayed exactly as the MAF table is. Then simply copy and paste special, multiply by %.

[BTLD_LS1]

Correct, fuel trims are closed loop. The problem is that if you leave closed loop from a cell that has a positive fuel trim, that fuel trim gets locked in and added to your PE ratio. So if you are +7 LTFT in the cell right before you enter PE and you're commanding 13:1 in PE you will end up with 12.15:1 (13/1.07). If you enter PE from a cell that has a negative LTFT the LTFT locks in at zero for the duration of that PE run and you command just what you have your PE set to.

You're correct, you need to use the histogram and add the appropriate amount to the appropriate cells in the MAF table to bring your fuel trims down.

You just need to click the green play button at the top to see the data populate in the charts and histograms but for the sake of getting the MAF dialed in you'll want to right click on a histogram and click 'load all data'. That way all the data for the run is populated and averaged.

That right there explained more then I could have ever hoped for, thank you

[Firebirdjones]

Wow I feel so much better that someone else needed that explaination too
I now only have to figure out exactly how the STFT and LTFT histograms coincide with the MAF tables.. I don't quite have a grasp on that yet.
I was looking at the histograms and see blocks with -2 (running rich and pulling fuel?) and some with 0 and some with +2 (running lean and adding fuel?). I think thats right. So I need to lean out the -2 blocks but I haven't figured out how to do that without messing the others up.

Can I simply change the numbers in the blocks to what I want and it will automatically change the MAF table to correct that?
I am guessing it's not that easy,,lol.

I think I understand your explaination as the MAF tables can only be adjusted for idle and part throttle driving up to the point where PE takes over at a certain throttle percentage. Anymore MAF tuning past that point doesn't have any influence on A/F ratios in PE mode.
Boy I hope I have that right,,,I may actually start understanding some of this stuff Larry.

[Firebirdjones]

Oooops sorry 5 litre eater,,,I just saw your explaination of the MAF and histograms,,,I will give this a try step by step and see if I can do something with it. It's a little overwhelming but I'm trying. Thanks again. Larry.

[r40734]

Excellent work Mr. Winters. The histogram config you shared (possibly plagiarized j/k) is golden.

Like FireBirdJones said, I have been led to think that the VE tables needed to be near perfect before messing with the MAF table, but I found that to be near impossible in my situation. My LTFT's were all maxed out at +25, and no matter what I did to the VE table, they would not budge from those max values. I recalculated my MAF table (using the old fashioned manual calculation method ) and the VE table instantly looked more normal. It still needs tweaking here and there, but it looks manageable.

Would I be safe to assume that I can now dial in the VE table to near 0 values, then go back and make a final tweak to the MAF table?

Why would the "norm" be to work on the VE tables first if the MAF table is that far out of whack?