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Joined: Jan 2003
Posts: 115
CEG\'er
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CEG\'er
Joined: Jan 2003
Posts: 115 |
Originally posted by bnoon:
Originally posted by RTStabler51:
Greg are you saying that a specific vehicles factory MAF is not calibrated for X size injectors that come in the car and that the injector size is programmed into the PCM and it does whatever it does?
Say for example if I was going to put 24# in my car, and I added a say a 96-98 or Mark VIII MAF to corralate (sp?) with the injectors.....would that work?
Or is my thinking wrong?
I'll tried to dumb it up as much as possible... No offense to you or anyone else...
Your thinking is wrong. MAF tables are made up of calculated values of air that pass through the MAF at certain transfer voltages on a flow bench. These MAF tables are engineer set values in the ECU once they are figured out on the flow bench. Now, with those known flow numbers, engineers can make calculations on the intended engine size, cam duration, intake volume, intended load, etc. etc. etc. to make a base calculation in the ECU before heading to an engine dyno. For X amount of air, you will need Y amount of fuel from your Z sized injectors. (there are also many variables to calulate load too, but they're all based off of this very basic principle of air and fuel)
You change the size of the injectors, you have to make changes somewhere in that A/F equation. The way the MAF guys make their changes to "tune" for larger injectors is by adding resistance to the transfer circuit. Instead of needing Y amount of fuel for X amount of air, the MAF tells the ECU that it's getting the original amount of air minus a percentage increase in injector size. X becomes .8X amount of air, requiring only .8Y amount of fuel, from 1.2Z sized injectors.
One MAF that came on a car with 24# injectors does not have to equal another MAF that came on another car with 24# injectors, electronically or in physical size.
See now this makes more sense to me than what you said before. Still differ on some things.. but non point in arguing...
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Joined: Sep 2000
Posts: 3,223
"Absolut Rara."
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"Absolut Rara."
Joined: Sep 2000
Posts: 3,223 |
Note that I wrote most of the below before Brad's post, so some of it is a bit redundant. I left my computer for awhile before finishing it . . .
Let me see if I can throw down a little 101.
A Ford MAF sensor measures the mass of air flowing into the engine over time. Hence the units being either Kg/hr or lbm/hr. Nothing more. The MAF does not care about the size of the injectors, or any other component of the engine. Much like an Engine coolant temp sensor doesn't care what size your injectors are.
An accurate MAF reading is only guaranteed when the MAF is used in the full intake tract it was originally calibrated with, ie the stock stuff. If you change anything from the air filter to the throttle body, the transfer function will no longer be accurately calibrated. A good tuner can compensate and "fix" the transfer function properly in the pcm, but that is a different subject.
In an effort to sell more parts, the aftermarket MAF companies have started tweaking thier trasnfer functions so that they will more or less function w/ different than stock injector sizes without changing the pcm. They do it in the same method that brad described above, by offsetting the transfer function by the same % difference as the new injectors are from the stock ones. The PCM now thinks far less air is entering the engine, and therefore far less fuel is asked for. Because the injectors are larger now, the total amount of fuel almost balances out. ALMOST. Aftermarket MAFs are notorious for inaccuracy and poor quality control, so the stock trasfer function is rarely accurate. Further, because the PCM is thinking there is far less air entering the engine than there really is, the PCM can never do the load calculations properly (which is a major factor in determining timing).
In conclusion, using a MAF meter, or MAF signal modifier to compensate for different size injectors is a HACK mod, and prone to poor results in overall performance (usually driveability suffers, as does low rpm performance).
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Joined: Oct 2002
Posts: 609
Veteran CEG\'er
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Veteran CEG\'er
Joined: Oct 2002
Posts: 609 |
Here's a great article on EEC technology. It's based on EEC IV, but much of the info carries over to EEC V also. There are transfer function tables and all kinds of good info there. Software operation description begins on page 22, after some hardware and memory location information. MAF info starts near the bottom of page 48.
Be sure to check out the parent directory for that file as well -- there are tons of articles and things there. 
Marty
98 SVT, Black, No. 786, May 7, 1997.
K&N, MSDS, Xcal2, Tint, Antennas, Big Gulp(R)-Sized Cupholder, Rear Dome Lt., Koni/Eibach, DMD, Pre-98 Sails, Brake Cooling Deflectors, Sidemarkers, Etc.
147K+ Miles
"Get the Door - It's GrooveNerd!"
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Joined: Jun 2000
Posts: 2,621
Redneck Troll
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Redneck Troll
Joined: Jun 2000
Posts: 2,621 |
Originally posted by Smokeshow:
Originally posted by bnoon:
Originally posted by RTStabler51:
Greg are you saying that a specific vehicles factory MAF is not calibrated for X size injectors that come in the car and that the injector size is programmed into the PCM and it does whatever it does?
Say for example if I was going to put 24# in my car, and I added a say a 96-98 or Mark VIII MAF to corralate (sp?) with the injectors.....would that work?
Or is my thinking wrong?
I'll tried to dumb it up as much as possible... No offense to you or anyone else...
Your thinking is wrong. MAF tables are made up of calculated values of air that pass through the MAF at certain transfer voltages on a flow bench. These MAF tables are engineer set values in the ECU once they are figured out on the flow bench. Now, with those known flow numbers, engineers can make calculations on the intended engine size, cam duration, intake volume, intended load, etc. etc. etc. to make a base calculation in the ECU before heading to an engine dyno. For X amount of air, you will need Y amount of fuel from your Z sized injectors. (there are also many variables to calulate load too, but they're all based off of this very basic principle of air and fuel)
You change the size of the injectors, you have to make changes somewhere in that A/F equation. The way the MAF guys make their changes to "tune" for larger injectors is by adding resistance to the transfer circuit. Instead of needing Y amount of fuel for X amount of air, the MAF tells the ECU that it's getting the original amount of air minus a percentage increase in injector size. X becomes .8X amount of air, requiring only .8Y amount of fuel, from 1.2Z sized injectors.
One MAF that came on a car with 24# injectors does not have to equal another MAF that came on another car with 24# injectors, electronically or in physical size.
See now this makes more sense to me than what you said before. Still differ on some things.. but non point in arguing...
This was my first post on this topic. Please, don't hold back. Nobody is arguing that I've seen, we're discussing...
http://www.bnmotorsports.com
"And I will strike down upon thee with great vengeance and furious anger those who attempt to poison and destroy my CEG brothers. And you will know I am the Moderator when I lay my vengeance upon you."
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Joined: Oct 2000
Posts: 6,760
Hard-core CEG'er
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Hard-core CEG'er
Joined: Oct 2000
Posts: 6,760 |
He's not accustom to Greg's 'tone'.... Originally posted by bnoon:
This was my first post on this topic. Please, don't hold back. Nobody is arguing that I've seen, we're discussing...
Ryan
Trollin!
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Joined: Aug 2001
Posts: 5,810
Hard-core CEG'er
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Hard-core CEG'er
Joined: Aug 2001
Posts: 5,810 |
Hahaha,  This information has been up for over a year and it is pretty relevant to much of this conversation. MAF information RIGHT HERE on CEG
Former owner of '99 CSVT - Silver #222/2760
356/334 wHP/TQ at 10psi on pump gas!
See My Mods
'05 Volvo S40 Turbo 5 AWD with 6spd, Passion Red
'06 Mazda5 Touring, 5spd,MTX, Black
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