I've been having the same problem.I have figured it out.I can get my idle,part throttle/round town blms in the 122-132 range by changing the injector contant alone.But everytime i get on the highway my blm go rich.Here is the frustrating part.I know how to get not only 128 blm on the highway BUT 128 int .It's by making very minor changes to a maf table in only one spot.



In fact I have many,many,many hours research & modifying the maf tables.I'm talking about a few gr/sec here or there in most cases,other than experiments.Not radical changes or rescaling.I can get 128/128 everywhere.Just by using my researched methods and targeting specific spots in the stock tables.These are just very minor changes too.I can't share this vast info on targeted recalibrations for specific areas though.Everytime I shared it before I was told it's incorrect,I guess it is.



Grumpy tells me it's not the best way.Then he writes the final answer on maf.But it's about rescaling the tables for a 3.5 digital? maf through a translator for a turbo v6.Which was more confusing than anything.Because grumpy says the maf tables are not tunable fuel tables.Now if you us his logic then look at the tables changes grumpy did to get the 3.5 maf to work.Having the ecm see 160 gr/sec at wot would have serious probles in the s/a and load.He was driving around rescalining the maf tables w/o adjusting the lv8.That should of effected the driveability very very badly.He did'nt even report a noticeable effect by rescaling.Just basically said he'll need to go over the lv8 stuff.No horrible side effects though.




Here is the thing,I have been told the maf tables are what the ecm uses to convert gr/sec from vdc.Just like the coolant sensor has a conversion table from volts to coolant temp.All my research indicates otherwise.Here is the facts.I have put all the gr/sec to 0 in the first maf table to 0.Then started my car and the gr/sec was 7 just like before.If the maf scalar tables was a voltage conversion table then my scan tool would have read 0 gr/sec for the voltage the maf sends at idle.The thing that did change was my blms.So that test indicates to me that the maf tables are not a voltage conversion table but a fuel table.The scan tool sees the actual gr/sec, not calulated by the maf tables.This means that there is a seperate conversion table in the code.


In fact the bua hak shows some kind of conversion from BIN(counts) to gr/sec above the first table.Not sure yet what it means yet though.But if there is a seperate conversion table to gr from vdc for the maf(not scalar)I would bet the ecm would use it too.Use it to help calculate fuel.Thats where the maf scalar tables comes into play.From what I see in the code the maf tables use injector lb/hour+actual maf signal to calculate(with lv8) fuel requirements .But I guess I'm beating a dead horse here.

 

This might soud silly, but did you clear the ECM's memory after you made the change? Maybe the values got loaded somewhere in RAM, and that's why the scantool values worked still.

 

Has anyone ever actually flow-benched their MAF tract? I mean, how hard would it be? Just blow/suck some air through the duct and log MAF voltage as a function of actual measured flow.

Anyone? While it won't account for backwash fluctuations (they could be induced I suppose), I'd bet it's a clean way to actually calibrate your MAF tables properly.

Come on, all the MAF is is a fken wire. You pass air (of whatever humidity etc) over it at a certain rate, and the heat of the wire is dissipated.

Take a wire, and pass a certain current through it (say, 2A). The voltage required to pass this current will be a function of the wire's resistance (say, 10V corresponding to 5ohms). V=IR.

Well, the power dissipated through the wire is P=VI=V^2/R=10*2=20watts. If the wire were perfectly insulated thermally, then it would reach an infinitely high temperature. As it is, heat loss occurs to the surrounding area of the wire to the airstream primarily. The amount of heat lost will be a function of the wire temperature and the airstream velocity.

So, you have a conservation of heat. And you have a heat transfer within that conservation. There is heat generated by the current-voltage through the wire, and heat lost by the cooling effect of the airstream. The amount of heat lost will be proportional to the temperature difference between the wire and the air, and also an increasing function of the airflow (let's not get into boundary layer theory). So for any given airflow, there will be a steady-state temperature the wire will come to if current is held constant (it is) and the flow is steady (oscillatory flows like backwash can skew results and dissipate more heat).

Oh yeah, the wire (Platinum usually) resistance varies with temperature. So if you know the voltage across the wire at a fixed current, you will also know the resistance of the wire (Ohm's law). And from the resistance of the wire, you will know its temperature (CRC Handbook, resistivity of Pt as fn of temp). Also from Ohm's law you can calculate the power dissipated by the wire. And from a few heat transfer calculations (if you know the airstream temperature and wire geometry), you can determine then what the air flow rate & velocity is.

Also, in order to do the calculations right you will need to make sure that the sampled section of air duct is representative of the cross-section (no edge effects, turbulence, etc) and well-defined (cross-section of entire duct compared to sampled section). This is skewed a bit when you cut out your fins & screens. You'd be surprised at the cross-section increase in the outer annular section by removing the fins and the impact it will have on making your MAF read low.

Another thing the MAF needs to do the calculation right is the airstream temperature. Since the gas flow rate is back-calculated from the heat dissipation rate, which is in turn calculated from the temperature difference driving force between the hot wire & the airstream, both the wire and airstream temperatures must be known. I'm assuming that there is a thermistor or something built in the MAF that does this correction, so the reported temperature is a 'difference'.

The largest undertainty in all this, although textbook correlations and endless theory can be used, is the air velocity-heat transfer correlation. This is the primary thing you are looking at in your MAF tables is an empirical curve that has been fitted to bench data. The other stuff is pretty exact (neglecting mfg tolerances and such), but the flowrate-heat transfer correlation is one which bears experimental data.

Anyways, enough ramblings. If someone would be able to share a flow-bench test result which showed "MAF Voltage -vs- Measured SCFM", it would be most interesting. I'd love to see the plot for a gutted MAF and a stock one in series. While not addressing all the MAF fundamentals it still gets you a whole lot closer in terms of calibration of your instrumentation compared to looking at the whole engine performance, assuming your fuel injectors are correct across the board, using your factory O2 sensor to determine the balance, and fudging here and there to get it close. I mean, you can correct and counter-correct the control action here & there, but if you're working with good data, isn't that better?

Does this make any sense, or is it totally irrelevant to underatanding what the MAF is doing? It's just measuring (although in a decidedly roundabout way) air flow. As you can see, the level of uncertainty can be minimized with a proper calibration. As with so many things, understanding and controlling every nuance of the in-between stuff is not needed if you make sure the 'black box' is doing its job of giving an accurate representation of the desired input-output relationship.

Most of what I've heard on calibration and tuning is really just fudging and compensating. That's fine as long as you know that's what you're doing. It's a more 'global' approach I suppose.

That's what I had...

 

Craig, at what pressure drop would you think to flow the maf??? I have an sf 1020 where I work, so it would probably be possible to flow my maf. I may need a little help with the wiring of the thing outside my car, as I'd have to remove it completely to flow it.
Bob

 

Well, 255grams/sec is right around 432.3 SCFM (1atm, 60F). May want to check my math. So as far as vacuum, I don't know but flow should be in that range, around 450scfm max.

I guess if someone has a vacuum reading off their MAF ducting that would be a good read. Measuring variations in readings with different ducting would be good too I think, with & without filter, etc.

Wiring should be pretty straightforward. Probably if you run an extension from the car, you could log data through the ECM if necessary and just take notes of the flows/vacuum with the car in park / not running / on.

 

FWIW - Please try to stay away from using "FINAL ANSWER" in your title. This is usually done by Grumpy to post final answers on stuff. If you have a reply to his post then post inside that post instead of making a new one.

Tim

 

Ill have to see what I can come up with.

 

With all due respect I didn't know folks had a copyright on certain terms.....however I can understand what you're getting at....
As for the never-ending maf table controversy... I'm currently working on tracking down the GM engineers who actually wrote the code to find out what their original intensions were; (see my post-"maf table changes....again". There's some things that still don't make sense to me-OK, maybe I'm slow! ) I started with Gordon Killebrew to find them. Yes they're all retired now, so it may take awhile, but I really am interested/curious enough to try to find out the information! Once I get the info from "the horses mouth" I'll do my best to accurately pass it on.

 

This topic has just *somewhat* come up on the gmecm list. One of the members (I will keep him nameless, but he does show up here from time to time I think) did a little work towards properly calibrating a ported stock MAF.

He used the much published flow figures for a stock unported MAF at 570 cfm and then flowed his gutted and descreened one and got about 796 cfm. He then took this to mean that the flow of the modified MAF was 30% higher than the stock one (570/796 =~ 70). So he than decreased all gr/sec values in the scaler tables by 30% and also decreased the FI constants by 30%. He locked all the PE stuff and AFR adjustment stuff out, locked the BLM to 128 and took it for a drive. Then he fine tuned the tables to get INTs of 128 by tweaking the scaler tables. He then graphed his new figures against the stock settings and made sure that his new scaler tables followed the stock type of curve as closely as possible and also made sure he wasn't inducing any spikes to the curve. He then set all of the PE stuff and other fuel stuff back to where they were before the MAF recal operation. He now gets a max reading of 208 gr/sec (which is within the 255 limit ), instead of it maxing out at 255 around 4700rpm. I don't have the details on his setup, but it really shouldn't matter......

This seems like the way to go. Of course, one would pretty much have to get their setup as close to 128/128s as possible with a stock MAF before doing this, but it seems like the right way to go to me.

Thoughts?

 

Do you mean this post from there? Was/is a very interesting read.

 

Well, that is one of them on the subject, but I was actually referring to this one as it involves doing it without the use of a translator or a *different* bigger MAF (btw, the stock one is no longer a restriction after it is ported from what his findings reveal):

I obliged him on his offer and he shot me a copy of his work. I am forever grateful .

 

I like the approach. One big thing is missing though, which is actually calibrating your MAF directly.

When you gut a MAF, the airflow will be redirected away from the little sensing port, and the MAF will be biased low in that respect. Additionally, the total resistance to flow is decreased over a normal MAF, giving you a higher flow for a given dP. Anyways...

To really bring it home, I would suggest the following:

1) Fabricate a bypass in the ductwork to allow 'unmeasured' air to bypass the MAF. Make the bypass about half the diameter of the MAF passage.

2) Take the assembled intake duct with MAF and bypass, and log data on a flowbench, where you can apply a given flow through the duct and read the corresponding MAF voltage. You should be able to do this with a 12V supply and a multimeter.

3) Convert the SCFM airflow data to gms/sec, and plot up the gms/sec -vs- MAF volts in Excel. Fit a smooth curve to the data (log should fit well, maybe power law).

4) Look at the gms/sec corresponding to +5v. This is going to be around your max flow that you can read, right? So this will give you an idea of your system capacity. If it's too small, put in a bigger bypass.

5) Once you're happy with the max airflow that can be measured, take that number and divide it by 255. This will be your "MAF Scaling Factor".

6) Take all the gms/sec -vs-voltage data and divide the gms/sec by the scaling factor and transpose this data into the "MAF Tables" of the BIN.

7) Take the fuel injector constant and LIE like a DOG to your ECM (you've already lied about the airflow, right?). Take the ACTUAL FI constant and divide it by the scaling factor.

8) Understand that you are lying to your ECM, telling it that it is getting less airflow than it really is by a constant divisor. Also understand that you are lying with respect to your fuel injector size, so that the ECM will deliver enough fuel to satisfy the airflow lie.

9) All is well, your lies are internally consistent, and in the process you have recalibrated (REALLY calibrated) your MAF sensor AS IT SITS in YOUR ductwork.

Thing is, to do the above, you need to have access to a flowbench of some sort. OR, you could use a stock MAF and ASSUME that some fixed percentage of the flow would go through the bypass and not get measured, allowing a higher actual flow compared to the maximum measurable. However, this might not hold true. It would be a fair approximation though, and you could go back to the plug-n-fudge method of trying to get your BLMs lined out by diddling the MAF tables that way. I mean if you're gonna diddle the tables and you NEED more than 255g/s for the engine, then go ahead and put a bypass on there and lie about your FI size. It's all consistent...

 

My screens are out in my maf so that is the only change.But I can give you a winaldl data log with 128 blms everywhere.I have devised methods that will get me dead on without a flow bench.I can tell you where to mod the tables for idle,highway and such.But my maf is not extensivly ported.But I could use my "no screens" maf bin for a ported maf.Then dial it in from there.The more mods the maf gets to flow more air the lower the maf tables need to be.That is funny because the volts from the modded maf will increase over stock.So the established logic is not applying to these real world experiences.Not saying anyone is wrong.But My data suggest otherwise.That in fact the ecm does know the actual gr/sec/vdc directly from the maf.I will highlight some of the points.


Not one response to this fact.Here is my main problem...There seems to be no way to get a maf system 128 blms with my car w/o lightly modding the maf tables.Grumpy has said it's not the best way.But there seems to be no other way.

 

This was overlooked too.

 

Well I guess I just don't follow here. How is what he did that much different than what you are suggesting? I mean if the max flow rate of the MAF is a certain amount greater than stock and you use that as the divisor, wouldn't it take care of the issues you state about the higher flow for a given reading of the MAF and the biasing factor?

I agree that one cannot just assume that their system will flow what his will and use his tables, but maybe we really could use his 30% figure..... I guess I agree that it would be a bit better to map the voltage of his modded MAF versus a bone stock one, including the ducting, and compare to come up with the divisor, but if you are going to play with the tables to get 128s afterwards anyways, would it really make enough of a difference to worry about? Wouldn't just flowing the two sensors and using the difference get you where you need to be for starters anyways?

 

In following KVU's endless rants about maf tables, and everybody elses discouragement from tooling with them, I have one simple question that I think is the top of the fence that is dividing everybody.


If there is NO other table to do the things the maf table does, whether its right or wrong, is it not the only alternative? Strip the label from it "maf scalar table" and what you have left is a table that will adjust your affective BLM and LV8, Is that so wrong to use as a tool if its the only tool at your disposal?

 

If you are confused, you'd get further by asking a guestion, then going on a rant.

If you stopped to actually read and aborb what I'd said it would make sense. Or at least understand enough to form an intelligent guestion.

Your sneeky avoidance of using profanity, is just childish.
And yes, you still have some basic concepts about things Wrong.

 

I did'nt go on a rant.I just raised some points.Not one person have even responded to one of them.I've been just trying to tune my car without using the maf tables.I have raised my injector constant to 35 for 30 lbers.But even then there is some spots thats way rich or lean.I have found that changing the maf tables a very small amount in spots will yield 128.

The reason I posted this way was to not clutter up the "final answer" post.The use of profanity is my form of expression.I was'nt rtying to avoid it.I did it that way so we could see my words instead of ****.So could someone give me a counter point instead of..... This is about all you give me on the maf tables.Do a search on my un and you will see.So could you respond to the research I did instead of...... .Whats wrong and why?

 

Yeah, I suppose so. Just trying to be annoyingly puritanical. I mean, if you KNOW what your MAF gms/sec -vs- Volts relationship is for your particular duct, then it will take some of the guesswork out of the front-end effort. Granted, you will still be tweaking to get your BLMs and all, but you will be doing so from a known, unbiased baseline and applying correction factors. Might eventually lead to a better understanding of what the engine is doing, rather than assuming you're correcting for MAF uncertainties.

 

If ones does as I mentioned, and corrects things for the old MAF to 128s, and THEN recals the MAF tables, you'll be right reguardless. Granted you might have some top end tweaking because of boundary layers not being linear. But, to blindly recal the tables, just to get 128 ignores all the LV8 interfacing...

Getting a flowbench comparison would be nice for getting a rough estimate, but it can mislead you. The effects of reversion also vary as a function of intake velocity.

The in car variances from flow bench to in car can be huge.

Never underestimate what reversion can do.

 

Im not trying to add coals to the fire.
1. I dont think we need to talk about childish when certain peeps
do nothing alot of the time except for try to make the asker look
look like a fool for asking...

2. why punish a man for trying to learn more about what he already has to work with or the disire to learn ????

3. gertain members are very ,very smart about the GMecm
and thats a fact.. but that does not mean everything that person
says is carved in stone.

4. And for a quote about " you'd get further by asking a guestion"
Ive seen many q's arise from one question but certain peeps refuse to reply to a question that arises from one of his stone
answers..

Im sorry ,and do not mean to offend by any means but i guess
im just a little flustered - hidden profanity is not the way either but i totally understand where that person comes from.

 

If adjusting your maf tables, which I have also been doing just a little, is "lying" to your ecm, isnt telling it a different injector size than what you have also "lying" to a certain degree? I'm not talking about a complete rescaling of the maf tables, just a few little tweaks to bring the idle, low rpm stuff around a little better. I havent been able, as of yet, to get the idle @ or near 128 without everything else going to rich. Sorry to keep fanning the flames, but I'm just trying to get a better understanding of things.

 

Hi Guys:

I HAVE NOT changed any of the contents of the post. Just the offensive term that by-passed the swear filter. Sorry, but I see no need for that.

 

I see the rift is still here after all this time...

Craig, your incorrect about what happens when you remove the screens. The idea of the screens is to attempt to equalize the flow across the maf, but in essence what the screens do is create turbulence and slow down the airflow. Taking them out creates, in most cases, a high airflow reading since most of the air wants to pass through the middle of the opening, which is right where the sensing element is. If you have a bend immediately in front of the maf this effect is lessened at low airflows and is negated and at some higher flows will read the opposite and be less than actual. What happens after the maf can also have an effect on the readings but usually not anywhere as much as the front side. You can verify this if you want by borrowing someone's gutted maf and throwing a screen on there, or by taking yours out and recording the changes. Its not impossible to correct for either, it just takes time like anything else. Getting it dead on is also unique to any intake setup and where the maf is in the tract.

Now I'm gonna go back to watching everyone bang their heads on the wall.

 

NOWAY Punk! You will help us figure this out too!

 

Well, here would be where we could compare MAF tables on Pontiac apps and Chev apps to see how different they are (or aren't) to settle the discussion on how the MAF reacts to different ducting setups..... Or at least how much we should worry about it, right?

Now, if that reveals that Pontiacs and Chevs both got the same cal for the MAF tables, I would see nothing that really discourages from following the method I posted about........

 

This is correct in regards to fluid dynamics. The fluid next to the walls will move slower than the fluid passing down the middle. And since you are "cramming" fluid down the MAF tube, it will tend to want to go down the middle where it can travel faster. So now "most" of the fluid will hit the heated wire area and get measured. I'm no physics PHD, but I can't see where removing the screens does anything but good for the flow of the MAF and according to the laws of physics and fluid dynamics it should help to direct more air to the center to be measured.

~M~

 

Having more aire flow into the center seems like a good idea, but if the maf is calibrated with the screens intakt, you would think the designers knew this when programing the ecm to begin with. Thus you would get slightly wrong readings unitl you recalibrate the maf. Or maybe im wrong, i dont know, back to the hole in the wall i came from.

 

Youre right, the stock tables are setup for a screens intact setup... I mean, thats what they were working with, why tune for something youre not using? I'd imagine theres no difference between Camaro and Firebird BIN files because the readings just cant be skewed enough that would be worth fixing. Cars werent all that close off the line anyway, why bother with nuances?

 

.The screens are there to break up the air flow.To create even pressure through the inside of the maf for acurate readings.The screens create a vortex.Now if you mod the maf then put sreens back in there,that would be the best way.Might need different screen though.That is a lie,since when was FINAL or THE a bad word.You edited my post and I think that crap.Delete it or block kcuf.But dont change what I have wrote.I like you alot glenn but your from canada and I guess don't understand "profanity".
I say fu*k when I stub my toe, not say "by george that hurt"(not sayin peeps from canada do,btw).I've walked up to a friend and said "what the f*ck is up".It was not a form of agression or frustration.Just me being myself.I know bikers that use profanity.Someone tell them they're childish.I THOUGHT I raised some valid points on maf.Plus shared my research with nobody to help interpret it.It just seem like everyone is just skimming this stuff.Since this went soo bad I have a new idea.I will write a "fictional" piece on tuning maf.I will have to find some other site to host it.I'm sure it would cause alot of problems here.I will use profanity AND discuss how to get a maf car running correct,including a hella lot on the maf tables .I will be contacting some maf guys here to share thier research in the field.That way this "fictional" piece will 100% complete and correct.

 

Talk about biting the hand that feeds you...


You're going to throw away a resource over a few swear words? Go to a church and start pop'n off like that and see what happens... Its not that your personality is wrong, its that there are boundries in society that we have to live around, it just so happens that this site (or at least this board) has opted for a cleaner atmosphere, you should certainly respect those wishes and keep your posts technical without the attitude and insults. I've watched you get frustrated at people not answering your questions, at first I respected your work efforts and posts, now you come across arrogant and childish, so far you haven't done anybody a "favor" and you're only jabbing at the well respected members who have been a tremendous resource to the tuning community. Nobody here gets paid for this, and its not your right to come in and get pissy when you dont get "free money". I recommend you think about it and try to retain a relationship here where you can keep working with some key people. Just because you dont get the answer you want it doesn't mean you didn't get the correct answers. Lighten up, show respect, and watch yourself get further faster. This route can only end with a ban.

 

It never ceases to amaze me how touchy folk get over maf!!!
Please everybody take a chill pill!
KVU-yes there's a bias here-I ignore it and sort thru the BS to learn.
I've found that it's just too easy to type out words on the internet that come across with an attitude, so I try to be carefull how I word things.....(some folk type whatever-but I'm not their mother so I ignore it. )
I'm just a relative rookie here, so I have a lot to learn-I read info here-but if it doesn't make sense then I research further elsewhere.
As for maf tuning.....I'm still waiting for more call backs, but so far;
it looks like both "sides" are right....
If you change your maf tables it affects all the tables based on lv8 and if you mod the maf it changes the flow; but in the real world... if you "lie" to the ecm about a few things it will still work just fine; if you change the maf and maf tables too much you'll need to pay close attention to anything calculated off the lv8. If you have a wide band you can easily keep it safe.
Small changes-don't worry about it! Yes you could get **** rententive and want to get it "perfect" but it ain't a perfect world and GM lied to the ecm a bit here and there too....
Anyway I've got mine working just fine with all my mods-so I won't argue the point any further!

Later everybody, and relax, have a beer!

 

Now you crossed the line. I removed the offensive word and the word "FINAL" from your "Subject Line" (along with other posters that "quoted" your offensive title). NOT ONE WORD of ANYONE's post was changed. And now you've crossed the line by accusing me of something I never did. Shame on you!

On this whole subject, someone privately said it best, "People aren't interested in the truth - just what they WANT TO HEAR (or WISHED were true)". It seems when people don't tell them what they want to hear, they go "on and on and on" until someone tells them WHAT THEY WANT TO HEAR. The TRUTH is not based no a "public opinion poll".

I've avoided this topic because after a LOT OF TESTING the MAF system on Thirdgens, you are dealing with a system that is affected by elevation, temperature and humidity - Sorry but it's FLAWED as implemented on Thirdgens - GET OVER IT!

There is no point to trying to being 128/128 perfect because if you change your elevation, temperature or humidity, the MAF will no longer be 128/128 perfect. I've been there already. You are banging you head against a wall.

If you want 128/128 perfect that will remain so in virtually ALL conditions (with proper tuning)...you KNOW the answer. Stop beating a dead horse.

So here is what you want to hear, "Do as you want with your car and change your MAF tables as you much as you wish".

But please drop the subject. This thread is now closed.

AND DON'T EVER CROSS THE LINE AGAIN. This is your one and only warning.