MAF count tables
- Thread starter norbs
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The MAF portion of the ECM's stored program is fairly complex but I'll see what I do here.
As I think you know, the MAF sensor puts out a frequency that increases with airflow. The ECM measures this frequency using a counter that counts at a fixed rate. Low frequencies from the sensor are slow and produce a high count while the high frequencies (lots of air) produce a low count. The range is 1927 to 437 based on the frequency range of sensors we use. The count gets subtracted from 1927 to produce the index to the MAF tables. These tables basically tell the ECM how many grams/second of air is entering the engine so it can do the fuel calculation.
To answer your question regarding the fuel mixture ... increasing a MAF table value will make the fuel mixture richer at that airflow. You have no control over the MAF output frequency but if you tell the ECM that for a given frequency (count) it is more air flow (gm/sec), then it will spray more fuel. It also works in reverse if you want to lean the mixture.
Dennis
As I think you know, the MAF sensor puts out a frequency that increases with airflow. The ECM measures this frequency using a counter that counts at a fixed rate. Low frequencies from the sensor are slow and produce a high count while the high frequencies (lots of air) produce a low count. The range is 1927 to 437 based on the frequency range of sensors we use. The count gets subtracted from 1927 to produce the index to the MAF tables. These tables basically tell the ECM how many grams/second of air is entering the engine so it can do the fuel calculation.
To answer your question regarding the fuel mixture ... increasing a MAF table value will make the fuel mixture richer at that airflow. You have no control over the MAF output frequency but if you tell the ECM that for a given frequency (count) it is more air flow (gm/sec), then it will spray more fuel. It also works in reverse if you want to lean the mixture.
Dennis
Thanks for the explanation, I can malke my maf give any freqency i want. That is why i want to tinker with these tables, since no one makes a chip to go enough grams/sec my car will flow. I am using a 97mm abaco maf sensor that i flash the sensor with a calibrated tables. I can make it output a ls1, ls6, zo6 maf whatever i want.
But you have to keep in mind, no matter what you manipulate the maf to do, there's a reason the top two maf tables all read 255 output even though the input side of the graphs keeps (what it sees from the maf) keeps on increasing in values.
It's an 8 bit computer. It's maximum calculatable value is hex FF (decimal 255)
You can manipulate the tables all you want, the ECM's only going to calculate to 255.
Street Lethal
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- Oct 8, 2006
norbs said:
255 g/sec is max in closed loop....
Mike Licht
I was here first
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255 is max no matter what, 8 bit computer
- Joined
- May 27, 2001
The MAF he's using can be completely rescaled via software. 255 on this MAF could be 10,000 CFM. (Not really but you get the idea)
The problem with what youre trying to do is youre going to lose a lot of resolution in the sensor.
The problem with what youre trying to do is youre going to lose a lot of resolution in the sensor.
Street Lethal
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JayC said:
Exactly, the MAF is subjected to 255 g/sec during transitional load, but in PE, you can fudge the numbers. It works fine, so long as you have adequate injector sizing, and you know how to tune for it. The only thing I don't agree with is the loss of resolution at WOT, because I would then ask, what resolution at WOT (open loop)....?
I've just started looking at the ECUs in these cars a few days ago, so forgive me if I'm not up to speed (I've only had my car for about a week now...)
Can you put the computer into a MAF fail mode and use the pressure sensor for all your load calculations?
Can you put the computer into a MAF fail mode and use the pressure sensor for all your load calculations?
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- Aug 1, 2003
maf isnt tied into the ecu so ecu has no idea of pressure in the engine,
the Turbo buick has a 2bar map sensor but its only there to drive the analog dash indash led boost gauge
there are speed density chips (turbotweak 6.0SD ) that with powerlogger and a 3bar map sensor allow you to get rid of the maf
aftermarket ecus like dfi ,fast classic (speedpro) and fast xfi run in speed density so no maf needed on those systems , and fast classic and xfi run their own wideband and can be set to correct fueling based on user programmable A/F tables
the Turbo buick has a 2bar map sensor but its only there to drive the analog dash indash led boost gauge
there are speed density chips (turbotweak 6.0SD ) that with powerlogger and a 3bar map sensor allow you to get rid of the maf
aftermarket ecus like dfi ,fast classic (speedpro) and fast xfi run in speed density so no maf needed on those systems , and fast classic and xfi run their own wideband and can be set to correct fueling based on user programmable A/F tables
not to mention the translator systems that have the rescaled Extender series chips. The range has been extended to 768 grams/sec in the Extreme series,
The MAF Pro works as a speed density conversion, and can use the rescaled chip designs. Along with other features.
Lots of ways to go. But the stock ECM is quite primitive in comparison to the LS1 stuff.
Bob
The MAF Pro works as a speed density conversion, and can use the rescaled chip designs. Along with other features.
Lots of ways to go. But the stock ECM is quite primitive in comparison to the LS1 stuff.
Bob
Street Lethal
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But here is the thing though, if the stock 255 g/sec equation is as follows....;
CFM x .5663 = Grams/sec ... 255 gms/sec = 450 CFM
.... once you hit WOT, the 450-CFM barrier has immediately been broken under boost, so the question here is, how is the stock '7148 able to compensate for fueling if the stock MAF is allegedly out of resolution immediately after 255 g/sec? GM obviously pre-configured what they felt was the right tune for up to 15-psi in the prom. But once boost is increased thereafter, larger injectors, and the hammering down of their pulse width would come into play, but it was still being done w/out a translator, because the MAF was maxed out a long time ago. I guess what it all comes down to is the ability of the driver. Those who don't run a MAF translator, and who burn their own chips, don't care if the MAF runs out of resolution because they will simply tune the VE until they get it right. But those who don't burn their own chips, get a chip burned close enough as a base, but then implement a translator so they can have double the resolution of the stocker, and not have to worry about tuning PW when the MAF will compensate fueling for them.
CFM x .5663 = Grams/sec ... 255 gms/sec = 450 CFM
.... once you hit WOT, the 450-CFM barrier has immediately been broken under boost, so the question here is, how is the stock '7148 able to compensate for fueling if the stock MAF is allegedly out of resolution immediately after 255 g/sec? GM obviously pre-configured what they felt was the right tune for up to 15-psi in the prom. But once boost is increased thereafter, larger injectors, and the hammering down of their pulse width would come into play, but it was still being done w/out a translator, because the MAF was maxed out a long time ago. I guess what it all comes down to is the ability of the driver. Those who don't run a MAF translator, and who burn their own chips, don't care if the MAF runs out of resolution because they will simply tune the VE until they get it right. But those who don't burn their own chips, get a chip burned close enough as a base, but then implement a translator so they can have double the resolution of the stocker, and not have to worry about tuning PW when the MAF will compensate fueling for them.
Street Lethal
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Mike Licht said:
Resolution is only used for part throttle, because you can use the PE tables for tuning WOT....
The stock setup ran right at the 255 gram limit. The 'old school' method of tuning was to throw a bunch of fuel in the PE tables and tune the car with fuel pressure. Matching injector size to the boost/ HP of the engine. This works fine on a turbo car with a small to moderate sized turbo since the high turbine pressure creates a downward slope to the top end of the torque curve, so running the injectors static at the top end creates a constant flow of fuel to match the flat HP curve.
With any single-point calibration method such as this, its only 'right' at one boost setting.
However, modern 255 gram chips have adjustable settings, Max Effort, TT chips and the Commander series have user adjustable fuel settings so you can tune the chip to your car.
The other method (proprietary to the Extender series) is to rescale the airflow reading in the ECM. So with an Extender, 0-255 in the ECM really represents 0-512 grams/sec of air. This is enough to go "really fast". When the crowd starting to go "fast fast" the 512 gram range was not sufficient to get the 72lb injectors up to full pulsewidth. So the Extreme series was developed. These read to 768 grams and are enough to run 96lb injectors without special tricks.
The range re-scaling has many other considerations which affect driveability (right Norbs?). The current generation of Extender chips have near factory driveability.
The bottom line is that modern chips have several methods to achieve maximum performance and driveability despite the inherent limitations of the stock ECM.
B
With any single-point calibration method such as this, its only 'right' at one boost setting.
However, modern 255 gram chips have adjustable settings, Max Effort, TT chips and the Commander series have user adjustable fuel settings so you can tune the chip to your car.
The other method (proprietary to the Extender series) is to rescale the airflow reading in the ECM. So with an Extender, 0-255 in the ECM really represents 0-512 grams/sec of air. This is enough to go "really fast". When the crowd starting to go "fast fast" the 512 gram range was not sufficient to get the 72lb injectors up to full pulsewidth. So the Extreme series was developed. These read to 768 grams and are enough to run 96lb injectors without special tricks.
The range re-scaling has many other considerations which affect driveability (right Norbs?). The current generation of Extender chips have near factory driveability.
The bottom line is that modern chips have several methods to achieve maximum performance and driveability despite the inherent limitations of the stock ECM.
B
Street Lethal
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.... I remember when we used to discuss this on ThirdGen.org, and Grumpy (Bruce) used to insist that the ECM would switch to Alpha-N Mode when the MAF was pegged @ WOT. The only thing with third gens though, is that the MAF never pegged at WOT, the injectors might have went static at one point or another, but the MAF continued to measure air well under it's resolution limit, throughout, even with ten second cars. Boost is obviously a different scenario, but then again, Alpha-N Mode was never really encouraged to be used with forced induction. These newest features that Bob was just explaining are unreal though. I would like to try and implement them w/the '7730 in my 1990 GTA, as opposed to just running the $8D mask but w/boost reference added, because then I would have to start from scratch, and rewrite code. The $59 code is an option, but I'm one of those rare few who prefers MAF over SD. It's a shame I can't adapt the '7148 to the V8, I mean I'm sure it can be done, but then it's the same problem w/the $8D mask, even more research, and rewriting the code.
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