Need help with understanding MAF adjustments.

[dfe1]

dfe1,
Fudging may or may not be needed regardless of the methods but it is for sure necessary if you do a "work around" tune and then the issues that remain, that people put up with, are sure to arise under changing conditions. At my age a lifetime is not too long but I have put in the time to get it right.

I guess it all boils down to what you're trying to achieve. I've always taken the approach that it's best to achieve the desired results with the fewest changes. With respect to fuel flow, if the engine makes maximum power at 12.9:1 it does't care how that's achieved. The problem I see with making changes to the MAF table is that it's a relatively esoteric table for anyone other than a veteran tuner. If something goes wrong with a vehicle and someone else has to troubleshoot it, there's a good chance that changes to MAF table will be missed. That's obviously not an issue if you're tuning your own vehicle, but is a problem for a customer who goes down the road. The other potential issue is that if you change too many things, you wind up chasing your tail when a problem arises. My whole reason for responding to this thread isn't to tell people how to tune, but to hopefully save some guys from a head-bashing marathon in the event of a problem either during or after tuning.

[Dirk Diggler]

Ususally if a customer comes to me with a borked tune i start from scratch anyways. 6 and 1/2 dozen of the other

[VetPet]

As a novice to the tuning world, I've been doing a lot of reading and researching this winter as I'll have to wait until spring for the chance to tune. The question of tuning the MAF has been rolling around in my head and this post has certainly brought up some interesting thoughts.

All of the information I've read so far does suggest that the MAF table does not need to be adjusted. The assumption here being that the MAF is properly calibrated from the factory within an acceptable tolerance. The MAF is a measuring tool and will provide the correct input based on what it sees. Changing your intake will provide cooler air than from under the hood but you won't change the volume entering the engine, only the mass (weight) of the air. That's why it's called a Mass Airflow Sensor and why the measurement is in grams/sec. The same type of conclusion can be drawn with reference to the IFR table. Unless you're changing your injectors to other than stock, why mess with it?

Before I put my car away last fall, I was able to get some scan data before and after installing my cold air intake. When I compared my LTFT's, the jump in values from before the installation was doubled or more. What this told me was that my engine was being fed a much higher quantity of oxygen than before which in turn required more fuel. Since the MAF is the primary air sensor, it must be reading correctly, otherwise the LTFT's wouldn't have changed so much.

There's one other thing that I've read which might surprise a lot of people. Most opinion is that the MAF does not handle throttle transitions well and that the VE table is there to help in these situations. Apparently, the MAF doesn't need the help of the VE table at all and is quite capable on it's own. The VE table is there as a backup in case of a MAF failure and open loop operation during cold start. At WOT open loop operation, the MAF signal is used and thus the need to adjust the PE table using a WB02 to compare actual AFR vs Commanded AFR.

I've still got a lot to learn but it is these types of discussions that make you think and get a better grasp of the concepts and strategies of EFI systems. My thanks to all of you.

[Dirk Diggler]

I am done everyone has their way of tuning and we will disagree to the end of time. I have spent countless hours tuning my own car and other peoples cars, are my ways right I guess we will never know. VetPet can you point me to any references which state the maf doesnt need to be touched.

If the injectors are calibrated right, pe set to 1.13 ve table dialed in in SD mode and you hook the maf up and you either see your trims go positive or the WB go lean what do you do?


Mater of fact I can post logs where the ve table was dialed in in SDmode and as soon as i went back to MAF operatoin the WB read 7-10 leaner makes sense to me that the maf needs to be dialed in at this point

[jfpilla]

VetPet,
Your too modest.

Dirk,
I don't think he's saying not to use it but just the opposite. I think he's referring to an old belief expressed in many posts.

"If the injectors are calibrated right, pe set to 1.13 ve table dialed in in SD mode and you hook the maf up and you either see your trims go positive or the WB go lean what do you do?"

Great way to put this question. I feel your Pain.
Joe

[Redline Motorsports]

To all;

Thank you very much for expression all your views. I always get concerned when asking some of these questions but they always yield some great debate and ideas.

It has become quite apparent that the individuals who responded to this post are looked at as "advanced" members of this forum. I have spent more hours with a pad of paper taking detailed notes from all of these threads and it is much appreciated.

I guess if you are going to keep the MAF in the tuning equation, it needs to be at least checked after a VE tune is completed to make sure that it hasn't affected the VE tune.

Before I got into the tuning I always had other shops tune the cars we built. There approach, now that I understand the tuning better, was one of smoke and lights.

Lets keep the thread going!

Thanks

Howard

[caver]

My understanding is that when the maf is connected the pcm uses that input exclusively with the VE table used to make sure the values are sane?

Every car I have done has had commanded afr miles from actual therefore I believe it is neccessary to adjust the maf tables.
I autotune the MAF as a matter of course.

[joecar]

Thank you very much for expression all your views. I always get concerned when asking some of these questions but they always yield some great debate and ideas.

This thread is a good read, and we're all able to discuss and respect other people's opinions... :two thumbs up:

..."advanced" members...

Yes, there's smart and knowledgeable people here, and I've been learning alot from them; thanks to all!

...if you are going to keep the MAF in the tuning equation, it needs to be at least checked after a VE tune...

that's what is comes down to: checking and not making assumptions.

Lets keep the thread going!

[joecar]

So, is there a summary of when (what conditions) the airflow is from the MAF and when it's from the VE table...?

Edit: Oh, I just saw this thread: showthread.php?t=1815

[VetPet]

[quote=Dirk Diggler]I am done everyone has their way of tuning and we will disagree to the end of time. I have spent countless hours tuning my own car and other peoples cars, are my ways right I guess we will never know. VetPet can you point me to any references which state the maf doesnt need to be touched.

Dirk, I'm referencing a book by Charles O. Probst, Corvette Fuel Injection. I'm sure you've probably heard of it. If you haven't had a chance to read it I would certainly recommend it. I think the GM engineers working on the Corvette projects are a pretty bright group of people and wouldn't throw on parts without some thought. The EFI program doesn't recommend changing the MAF table unless you change to a larger MAF as well.

I'm not saying that adjusting the MAF table is totally incorrect. I'd just like to know what's really causing the mixture to go lean once you put the MAF back on. Is it really the MAF calibration or is the MAF signal being modified by some other sensor input that's causing the problem. It just doesn't seem right to try and recalibrate a measurement device unless you know for sure that it isn't right to begin with.

There's one either item that I found interesting in reading the above book. I was under the impression that if your LTFT's are positive that they affect fueling under WOT. If I"ve read correctly, once you're in WOT open loop operation, the LTFT's are out of the picture and have no effect. Your WOT AFR would be dictated by the commanded AFR based on your PE table values and MAF sensor input. I'll have to look to find the page reference for this.