Also I dont agree with changing the IFR because the computer reads incomming air first then figures out fueling and spark second. IFR changes are a poor mans fix a bandaid if you may. I agree with txhorns if the airflow of the engine is altered you have 1 or 2 ways of tackling it. Since neither can be trusted pick the lesser of two evils and run with it

 

I haven't had time to work on my car the past few days due to a few new changes, but I get her back today. I am going to test HumpinSS theory with a WB and see what I come up with.

 

I saw some major flaws in my VE table awhile back, so I went back to the drawing board today. This time I disabled everything that could get in my way (Proportional Idle, PE, LTFT, MAF, etc). I managed to pull the edges of my VE table into the right places, which I think will make a big difference...at the very least in SD, ha ha ha ha. Maybe it will help my airflow calculations too.

My VE table is starting to look a lot like the picture I saw (I think of Magnus' tune). Just a little more work...

 

You are all correct in your logic and reasoning. I certainly won't disagree with the basis. However, when faced with days and weeks worth of effort to get a MAF or VE tune spot on only to have it change from one weather condition to the next vs 15 mins using IFRs, I wonder sometimes if its all worth the effort.

In the end, we are trying to achieve negative LTFT at stoich without lean charges passed into WOT. In the end, even modifying the VE or MAF you are doing exactly the same as rescaling the IFR's. This is because when you assign more air you indirectly alter the injector pulse width. Whether by IFR or VE or MAF, the injector pulse width will be impacted exactly the same. So you wont be maxing out the injectors any more using either technique.

Just food for thought. Im not saying you are doing the wrong thing. I wish the MAF and VE were easier to scale.

 

It makes a big difference. Even if it changes, the closer you dial in your VE, the better the car will run. It takes a fraction of a second for STFTs to move. That fraction of a second is really a long time for your car. A big shift is bad.

 

As far as what to do about the MAF max values. Very few cars pull past 450GPM so in the LT1 Crowd we just flat lined there. Blower cars were usually the only ones that would and not much to do there but that is a whole other subject.

When we dyno we make sure it one of the logged values just to make sure

 

Ok. I have been messing with this junk all day. I had a thought I wanted to swing past you guys. How about multiplying portions of the tables by percent fuel trims? Anybody have some ideas how to smooth it out?

 

I started tuning today for the first time and played with VE and after that the MAF. The MAF Values I used were created from Redhardsupras spreadsheet and the car ran great with them. I got the VE tuned pretty good but not good enough because I was having some random knock retard but nut more than 1.9 degrees more than a handful of times. I know there was a post on here earlier about this but why do your trims get messed up after getting gas? After I filled up they went negative and slowly came back down after a 20 minute ride home.

 

way2slow, thank you for warm words, most people so far just bitched their their new MAF screwed up all their other tunes (DUH)

I also have a very similar problem, despite MAF and VE being tuned a zillion times, and having it really close to what it supposed to be, I still get knock. I was hoping it's old plugs/wires, so I changed them to new pimpy ones, but I still get the same <2deg knock in the silliest of moments (cruising at low rpm with barely any load on it), and I have very conservative spark/PE settings. if anyone has a good idea what should i scan for, please let me know. I've already ripped through the data, trying to find patterns of what could be possibly causing it, and I can't find anything. No tip-in, no sudden deceleration, none of the usual suspects cause this retard.
any ideas?

 

Yeah I had some knock in about 20 cells. I had about 40 cells of WOT and only 3 of those had knock, and that knock was only .35. It was kinda wierd. My PE and Spar settings are stock. Thanks for all the good work on the spreadsheet. I unfortunately wont get to do any tuning again for another week so hopefully then I will get the VE down and then try MAF again.

 

Hey Marcin, "our" methods worked just fine for me....

 

I know, they worked for another friend of mine too. He home ported his TB and did the coolant bypass, and when we scanned his VE's it was all seriously lean. One MAF calibration later (literally it took one try) his VE's all got back to normal without touching anything else but MAF.
My new personal discovery is how sensitive MAF is to airflow changes in general, not just in the pre-MAF section. I put in LS6 intake on last week, and recalibrated my MAF, and it looks like there's more airflow through the whole range. that's kinda cool, demonstrates that if something's holding up the airflow even past the airflow measuring device, the whole flow is still affected, not just a section of it. oh how i love busting up internet myths

 

Intresting. Should I attempt to tune my maf before tuning my VE tables? After longtubes ect I average a constant +9 LTFT while cruising.

 

I do both VE and MAF at the same time. As long as you just 'ignore' it by setting the fail frequency to 0, you gather frequency/airflow tuples for MAF, as you're collecting histogram values for LTFT+STFT for VE.
The cool part is when you plug both new tables in, and suddenly every works write and you get nice clean dead on VE values, trans doesn't shift like ****, and PE suddenly is smoother and without knock. And it also takes less time to do both at the same time
and stop screwing with IFR tables, people! you might be adjusting the mixture, but you're adjusting it through the wrong portion of the mixture, so while you might be fixing one thing, you're screwing up another. sorry, i ranted off there for a moment

 

Here is the reason....The IFR is a independent table and its effects are linear. The MAF calibration is a dependent calibration and changes will effect other tables.

Always change IFR. Never change MAF.

Can you make it work. Yes, but poorly.

Perry

 

However, there are a multitude of things that are DEPENDANT on the IFRs. Changing IFRs have global effects too which cause funny things like commanding an certain AFR but not achieving it. If your VE fueling tables are all mapped out correctly, then the one thing the MAF is dependant on is correct, therefore allowing you to calibrate it properly. This is b/c VE calcs must include an airflow aspect, otherwise fueling would be totally screwed if our MAFs failed. Since we can measure that airflow aspect, we can align our MAFs to report true combustable airflow measurements from 0 mph all the way up to whatever you feel like topping out at and for all rpms.

Always change IFR = always BS to your PCM about what you really are pushing

Never change MAF = never change the device that deals DIRECTLY with what the problem is here... airflow.

MAF calibration does not pick up a change in air volume when we deal with ported/aftermarket MAFs since it is not adaptive. When we mod, we not only change air velocity but also air volume. These sensors have the ability to be accurate so long as they know what to be accurate about. So what we're doing is measuring and redefining the airflow as the motor requests and uses. You can see graphically, at least in my case, that after all my mods, my motor uses about 20-30% more airflow than what the MAF is reporting. I could actually breakdown how much % off my stock calibration was at each individual MAF calibration point but that would take a lot more space than I already have. With this kind of precision, why not use the MAF for what it's for and tell it correctly what kind of airflow it will expect to see through its calibration?

Even if we're not 100% totally on, it seems like scaling IFRs is like throwing fuel in to compensate for extra airflow, but there's no airflow data to really target from. You add fuel or subtract fuel to produce whatever AFR you want, despite what the PCM commands and all this while making your PCM think it's got bigger/smaller juicers. Why not work with readily available data? I used to get IFRs scaled around before I knew too much about this stuff and the one thing i look back and remember is that yes my car put out 13.0 AFR on the dyno, but my PCM was commanding 11.7. So it sounds more like scaling IFRs is the "make it work" solution here. Now when i command 13.0, i get 13.0, or 12.5 or whatever I want. No guess work anymore, just tell it to do and it does. Stock GM 26#er IFRs and my car runs smooth, makes awesome power, and the EFI responds to command and correction as it should. Also, my MAF reports almost exactly the airflow the VE calcs come up with during combustion so there's no fueling confusion there since even if it's a biased decision b/w MAF or SD, they both show the same airflow.

Can I make it work? I did and it worked VERY VERY well, while being VERY VERY easy too

 

I'm still not sure why you'd want to in a sense "lie" to the PCM about your injectors. I'd rather slightly reshape the maf curve for the FTRA, descreen, and ls6 manifold. Thats just the way I see it.

 

Kinda like what redhardsupra said. If you force MAF-ignore (SD mode) you will be interested to see how those positive trims drop way down. might even be enough to drop negative. Mine sure did. Tune out your VE first, that way you're either close to or dead on commanded AFR. that's the whole point of getting your VE referencing correct, it's so when you command something it will go, "ok boss got it!" and be a productive little fuel map and do what it's told.

Once that has been accomplished. For that particular set of VE references (your whole VE table) there will be SD airmass calcs that are a parameter of your whole VE fueling equation. This is how the car knows how much fuel to use. Now here's another question: how do we know these SD airmass calcs are correct? Well, I'm not exactly sure how GM came up with them, but they are adaptive, and if your VE is tuned correctly then whatever values they may be, are the direct airmass calcs that allow you to command an AFR and produce it during combustion. These airmass calcs are what the MAF ought to be reporting. The MAF can sense changes in air velocity, though not completely, but defintely not volume. that's why the MAF is such a wonderful thing, it was designed as a user input device to create a user inputted function! It's something we can measure and fix! YAY

Once you are on your final VE that responds to as been commanded, tune your MAF shortly after. You will want to do this on a medium weather type day for your climate as well, as to anchor your tune in the center of your weather conditions. We all know cold tunes don't work well in hot weather so we do a medium tune that works it all kinds of weather. In TX it's been going from 40 up to 70 back down to 40 all in a few days and my tune has held up very well. No loss of driveability and drive hard and strong at WOT. I'm waiting for those 90 degree days to come back to prove my statements of late but I have a good feeling it'll work out just fine.

 

txhorns, not everyone is as patient or well versed as you in this area. For every success story like yours I hear 10 failures. While the technique you apply is simple the execution is not. For many, hours of logging, recal. and driving in different atmospheric conditions is just too much. Call me lazy if you like.

Ive tried your method and got some success, but it stuffed up too many other things in my tune - things like calculated cylinder fill, calculated transmission torque, calculated engine torque to name a few. With IFRs I can mod without having to readjust my MAF or VE every time.

Yup.

Yup. and Nup.

The problem is not airlflow. The problem is AFR.

If you are running SD WITHOUT a MAF then sure - I agree - get the VE right - its all about VE. If you run a bastardised MAF - then sure - I agree - get the MAF right - its all about MAF. Better to leave the MAF alone though .

If you DO run a stock MAF - that device has been calibrated correctly in controlled conditions to generate the most stable average airflow reading possible. You will not do a better job by road tuning based on the residual LTFTs that are impacted by air density and temperature variations.

It's people who bastardise the MAF by pulling the laminar screen and porting the aerofoils that have changed the MAF performance and so a recal. is necessary.

Commanded AFR is a byproduct of airflow and injector pulsewidth calculations and rescaling the IFR will not cause fluctuating AFRs. If you have stable TRIMS you should get stable fuelling at WOT.

IFRs, however, will offset the actual AFR for a given commanded AFR - I agree with you on that - but so what? What happens if you reach a state where the actual AFR reads the Commanded AFR and you STILL have positive or unstable LTFTs?

The goal is not to get the commanded AFR reading actual AFR. It is what it is and will vary from car to car. You just need to know what the diferential is so you can begin making LINEAR adjustments.

Tuning is about maintaining the correct AFR for the intended engine load and RPM. Im glad it worked for you. Im glad it worked for me. If anything this debate has shown is that there are repurcussions with whatever you do and with whatever approach you adopt you need to be prepared to deal with the consequences.

 

Your LTIT and STITs are off. As you sit during refuel the IAT goes up and your IAC resets at the increased IAT. Your IAC values are not correct. At startup ( IAT quickly drops) the LTFT, and STIT at zero, are added in and after 20 mins they've (LTIT and STIT) relearned.
Hope this helps some.