MAF question on FI cars
So replacing the MAF system with a MAP setup and using say... HP Tuners to tune would not be a fix for this issue? I know scaling has been mentioned before, and I guess is always an option.
Which do you think is the more desirable of the two for a... say 10psi LS1 setup?
Which do you think is the more desirable of the two for a... say 10psi LS1 setup?
Originally Posted by turbolx
Yes, and there's ways to work around this if you're creative. It's called "load scaling". Basically, you reduced the actual MAF output by the percentage the new MAF would be over the PCM max. To keep fueling accurate, injector size is scaled down by the same percentage. To keep load calculations accurate, engine displacement scalar is also scaled down by the same percentage. The nice part about this is that when done correctly, the tuning process remains the same. I.E.. a 5% commanded fuel change yields a 5% actual fuel change from the engine.
This keeps the acutal performance right on for all load based calculations (including spark, EGR, idle, et. al.) while allowing for significantly higher measured range. The primary downside is a slight loss of resolution at low flow rates, but since MAFs have an exponential transfer function there is a lot of resolution to give down low before experiencing any trouble.
This method works so well that Ford did the exact same thing on the production calibration for the GT supercar and still passed CARB emissions and all their internal performance standards.
This keeps the acutal performance right on for all load based calculations (including spark, EGR, idle, et. al.) while allowing for significantly higher measured range. The primary downside is a slight loss of resolution at low flow rates, but since MAFs have an exponential transfer function there is a lot of resolution to give down low before experiencing any trouble.
This method works so well that Ford did the exact same thing on the production calibration for the GT supercar and still passed CARB emissions and all their internal performance standards.
Launching!
Joined: Jan 2002
Posts: 299
Likes: 41
From: Detroit, Murder City
First, let me be clear. Either method can work just fine as long as the PCM has some way of knowing the actual air mass entering the engine at any moment. The whole trick is to spend a little bit of time with it to develop the air model correctly, whether it's a MAF transfer or a VE table.
That being said, my preference is the OE method of air mass measurement. The MAF sensor is very forgiving of changes in weather, varying boost levels, changes in actual flow (power), and temperature changes. In an ideal world, the MAF has a range just slightly larger than the maximum airflow the engine would ever have at sea level on a cold day, the PCM would have a calibration that represents the MAF transfer function's exact curve for the vehicle and installation, and "face value" models of engine displacement and fuel injector modeling. Depending on head and cam choice, 10 psi on an LS1 should fall pretty close to within the range of the OE MAF. This is the same way OE supercharged and turbocharged engines (Lightning, Cobra, 996TT, S4, C230, etc...) are calibrated. A close second is a slight scaling of these to accomodate the internal PCM limit (511.8 g/s).
If you really like speed density, have fun with that map instead. It seems to work just fine for Chrysler on their boosted applications.
That being said, my preference is the OE method of air mass measurement. The MAF sensor is very forgiving of changes in weather, varying boost levels, changes in actual flow (power), and temperature changes. In an ideal world, the MAF has a range just slightly larger than the maximum airflow the engine would ever have at sea level on a cold day, the PCM would have a calibration that represents the MAF transfer function's exact curve for the vehicle and installation, and "face value" models of engine displacement and fuel injector modeling. Depending on head and cam choice, 10 psi on an LS1 should fall pretty close to within the range of the OE MAF. This is the same way OE supercharged and turbocharged engines (Lightning, Cobra, 996TT, S4, C230, etc...) are calibrated. A close second is a slight scaling of these to accomodate the internal PCM limit (511.8 g/s).
If you really like speed density, have fun with that map instead. It seems to work just fine for Chrysler on their boosted applications.
Originally Posted by Lostpatrolman
And could anyone explain to me what on that page i would need to get to do a map sensor on my car? I got a 99 Camaro SS. I can get a hold of HPTuners so i just need teh map stuff, i think. Thanks
John
Originally Posted by 99SS-T
Ya im confused about that as well. How do you know exactly how much air is gettin into the engine with out a MAF? I kno wya put a MAP sensor in tehre but that doesnt tell teh engine how much air is goin in right? Like wouldnt ya be runnin rich on a hot day and lean on a cold day cause ya got hte same amt of boost BUT alot mroe air on a cold day? Hope ya can help me understand!
Also how sells the 3 bar setups? Thanks
John
Also how sells the 3 bar setups? Thanks
John
The ECU will do the fuel calculation based on the MAP sensor, RPM and what the VE table is. It will also have modifiers for air temp, water temp, TPS rate of change and a few other parameters that I can't think of right now.
Andrew
Launching!
Joined: Jan 2002
Posts: 299
Likes: 41
From: Detroit, Murder City
Originally Posted by 2001WS6Vert
Greg, were you the tuner & co-owner of Detroit Speedworks?
Just trying to help keep you guys informed with actual tech.
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Greg, instead of changing anything about a stock maf (leave the screens in etc), can the 512g/s limit in the computer be extended somehow to leave the lower calibration stock. Say you are running 16psi on a turbo set-up and around 4500 rpm you exceed the 512.....most folks crutch the PE vs RPM to add additional fuel over 4500 rpm. Anyway to extend the 512 to say 750 so the 0 to 512 stock calibration could be left alone without scaling the resolution?
10 Second Club
Joined: Apr 2002
Posts: 1,755
Likes: 2
From: Cincinnati, Ohio
Greg, you tuned my car a couple or so years ago. How's Turbo doing? You did a great job on my car. I actually brought it to you with a bad coil that was breaking up above 4500rpm. It really screamed after I fixed that. The evolution of fuel injection really goes from mechanical fuel injection like on the 70's VW's to the MAP system (early american throttle body), to the airflow sensor (kinda like a MAF with an air flap and potentiometer), to the MAF. I do believe your kind of taking a step back by deleting the MAF. If someone had a plug and play MAF offering which extended its monitoring capability you would probably see a wave of people buying it, like the OBX intercooler was.
Launching!
Joined: Jan 2002
Posts: 299
Likes: 41
From: Detroit, Murder City
John, remember I said "in an ideal world". With the demise of Pro-M, I'm not sure exactly who is taking up the void in the market for reliable MAFs with extended range. I have heard rumors of new MAFs available from a couple different places, but nothing concrete to my knowledge at the moment. If someone were to even provide the voltage-frequency convertor that Pro-M used to sell, it would allow GM guys to use one of the Ford (hitachi) style MAFs that the Mustang guys use at the moment.
Unfortunately, the 512g/s second limit is a hard one in the PCM. It has to do with the number of (hexa)decimal digits alloted to that variable in the customer's (GM's) code, not the actual calibration variables that are adjusted by the "tuner". Hence the reason load scaling works.
Changing the PE multiplier vs. RPM does indeed work to add fuel if you are slightly beyond the limit. Heck, I've even done this before. But in my continued learning, I have found it generally better to stay with the more flexible method of MAF scaling to avoid complications from weather changes, belt slip, etc. etc. etc...
Thank you for the kind words. Turbo is enjoying retirement. I can only hope my pension plan is as good as his. I'll tell him you said "hi".
One could fill a book with the history of fuel injection. I would think that a better one would be covering actual engine operation and the reasoning behind the need for certain controls and how to properly modify them, but there's no room for that in a single post. The Bosch "Gasoline-Engine Management" book is a great read if you're into this kind of thing.
Unfortunately, the 512g/s second limit is a hard one in the PCM. It has to do with the number of (hexa)decimal digits alloted to that variable in the customer's (GM's) code, not the actual calibration variables that are adjusted by the "tuner". Hence the reason load scaling works.
Changing the PE multiplier vs. RPM does indeed work to add fuel if you are slightly beyond the limit. Heck, I've even done this before. But in my continued learning, I have found it generally better to stay with the more flexible method of MAF scaling to avoid complications from weather changes, belt slip, etc. etc. etc...
Thank you for the kind words. Turbo is enjoying retirement. I can only hope my pension plan is as good as his. I'll tell him you said "hi".
One could fill a book with the history of fuel injection. I would think that a better one would be covering actual engine operation and the reasoning behind the need for certain controls and how to properly modify them, but there's no room for that in a single post. The Bosch "Gasoline-Engine Management" book is a great read if you're into this kind of thing.
Last edited by turbolx; Aug 2, 2005 at 04:09 PM.
How about a megasquirt with a 3-4 bar map? I am fine with the concept of using a map sensor and a MAF with the stock PCM. How does timing come in to play? How does the stock PCM decide to add or take away timing based on airflow? MAF? MAP? Or does timing not work like that? Here is my plan: Use the stock PCM strictly for timing for a turbo setup( i have HPTuners) and then use a megasquirt PCM for fueling. Would the MAF and MAP sensor provide all of the info needed to make the timing working for 12+ PSI of boost? The reason i would need a higher range than 12 PSI is because my turbos are sooo small and my motor is really big. I am trying to avoid doing an EDIS-8 setup for now so i can get the car running well enough to drive to a storage facility in CA.
Greg
Greg
No joke... if you wrote that book, people would buy it. I know I would!
Originally Posted by turbolx
One could fill a book with the history of fuel injection. I would think that a better one would be covering actual engine operation and the reasoning behind the need for certain controls and how to properly modify them, but there's no room for that in a single post. The Bosch "Gasoline-Engine Management" book is a great read if you're into this kind of thing.
For the record.You can run a stock MAF to 18lbs and have a set/reliable tune.As said before it goes into a locked timing/ A/F but it can be done and it will not change if tuned in right 
Launching!
Joined: Jan 2002
Posts: 299
Likes: 41
From: Detroit, Murder City
Originally Posted by disassembled
I am fine with the concept of using a map sensor and a MAF with the stock PCM. How does timing come in to play? How does the stock PCM decide to add or take away timing based on airflow? MAF? MAP?
I wouldn't recommend trying to run two controllers simultaneously on one engine for fuel and spark. This begs for problems and headaches when one doesn't know what the other is doing. Several people have already proven that BIG power can be made using the stock PCM on these cars if you understand how to properly control it.
Here is a link I had bookmarked from previous talk about a voltage to frequency conversion.
Finding a maf that flows 120#/minute is easy in a 0-5 volt output, such as a Big Air 2800 maf, but not in a frequency one for the GM cars.
http://www.slowcar.net/MAF%20Circuit.jpg
I'm not sure if anybody has tried this or not, i plan on trying, but i am still a few months away from having boost on my car.
Ryan
Finding a maf that flows 120#/minute is easy in a 0-5 volt output, such as a Big Air 2800 maf, but not in a frequency one for the GM cars.
http://www.slowcar.net/MAF%20Circuit.jpg
I'm not sure if anybody has tried this or not, i plan on trying, but i am still a few months away from having boost on my car.
Ryan