Maxing out MAF
08-06-2007, 10:49 AM
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Maxing out MAF When FI guys max out their maf's does the pcm go right to SD?
Just asking because I was thinking about this since the maf makes for nice driving around and fuel mileage but there are lots of FI cars that max out the maf. What exactly happens from a tuning perspective once the maf is maxed?
Just asking because I was thinking about this since the maf makes for nice driving around and fuel mileage but there are lots of FI cars that max out the maf. What exactly happens from a tuning perspective once the maf is maxed?
08-06-2007, 11:17 AM
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Originally Posted by MrDude_1
MAFs have nothing to do with "making for nice driving around and fuel mileage"
MAFs are a crutch used by OEMs to make OE engines maintain themselves within the given EPA guidelines. thats it.
MAFs are a crutch used by OEMs to make OE engines maintain themselves within the given EPA guidelines. thats it.
08-06-2007, 11:50 AM
#4
Originally Posted by My90Iroc
Even though this is off topic to my actual question, I'd like to hear you explain that statement. Last I checked the EPA is directly related to fuel mileage so I guess I'm not fully understanding your point.
the EPA is the Environmental Protection Agency.
they help set the emissions laws for every state except Cali.
because of the ever stricter emissions tolerances, the OEMs need a self-modifying tuning medium that will allow the motor to correct itself accurately enough to maintain itself within guidelines for a number of years.
the MAF helps them maintain that... that is why the OEMs are switching to MAF augmented (not MAF controlled, but its PART of the control) systems.. not for driveability or fuel mileage.
while they can be made to work, the GM MAFs used on our motors are FAR from ideal for a forced induction car. unless you require keeping it to meet local inspections, there is no good reason to keep it.
and to answer your question.. no.
the PCM just stays in the last cell of the MAF table. anything over 255 remains at 255.
however you can kinda get around that by modifying other tables (PE for example) to cheat around it... however thats really only good for supercharged cars as the flow VS RPM is fairly constant. there are guys doing this succesfully... Turbo guys tend to have to swap around to a true SD setup, because they are all over the map... but im sure theres atleast one person out there just past the edge of the MAF making something work.
08-06-2007, 12:11 PM
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Originally Posted by MrDude_1
no, CAFE is coperate average fuel economy.
the EPA is the Environmental Protection Agency.
the EPA is the Environmental Protection Agency.
Originally Posted by MrDude_1
the OEMs need a self-modifying tuning medium that will allow the motor to correct itself accurately enough to maintain itself within guidelines for a number of years.
Originally Posted by MrDude_1
and to answer your question.. no.
the PCM just stays in the last cell of the MAF table. anything over 255 remains at 255.
however you can kinda get around that by modifying other tables (PE for example) to cheat around it... however thats really only good for supercharged cars as the flow VS RPM is fairly constant. there are guys doing this succesfully... Turbo guys tend to have to swap around to a true SD setup, because they are all over the map... but im sure theres atleast one person out there just past the edge of the MAF making something work.
the PCM just stays in the last cell of the MAF table. anything over 255 remains at 255.
however you can kinda get around that by modifying other tables (PE for example) to cheat around it... however thats really only good for supercharged cars as the flow VS RPM is fairly constant. there are guys doing this succesfully... Turbo guys tend to have to swap around to a true SD setup, because they are all over the map... but im sure theres atleast one person out there just past the edge of the MAF making something work.
08-09-2007, 03:04 PM
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My car is pegging the maf but I havent went to SD though I plan to pretty soon. From what I have seen it never seems to make it to the end of the table it starts to stick around 57-60lbs.. If I clean it will make it to 67lbs for a few days and thats it. Then back to 57lbs and it gets really lean.
So I just tune it using the maf up to 57lbs and then you just have to increase the pe table richer than you should past that point. (ie it will cammand 10.5 or so but actually run 11.5 or wherever you need it.... )
Just make sure you start out rich at the end of the table and work your way up with the wideband until you get where you want. Thats what I have done so far and it works well.
My maf gives up about 5300 rpms and from there my pe table cammands richer to compensate.
What type of turbo kit and how many lbs are you plan on running?
So I just tune it using the maf up to 57lbs and then you just have to increase the pe table richer than you should past that point. (ie it will cammand 10.5 or so but actually run 11.5 or wherever you need it.... )
Just make sure you start out rich at the end of the table and work your way up with the wideband until you get where you want. Thats what I have done so far and it works well.
My maf gives up about 5300 rpms and from there my pe table cammands richer to compensate.
What type of turbo kit and how many lbs are you plan on running?
08-09-2007, 03:53 PM
#7
Originally Posted by MrDude_1
MAFs have nothing to do with "making for nice driving around and fuel mileage"
MAFs are a crutch used by OEMs to make OE engines maintain themselves within the given EPA guidelines. thats it.
MAFs are a crutch used by OEMs to make OE engines maintain themselves within the given EPA guidelines. thats it.
Just like MrDude_1 to bitch you out for a long time before he actually has on-topic information of any merit.
He must really hate himself if he has to go around finding peoples' faults instead of being a reputable and consistent source of information.
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08-09-2007, 03:55 PM
#8
Originally Posted by 2002_Z28_Six_Speed
Just like MrDude_1 to bitch you out for a long time before he actually has on-topic information of any merit.
He must really hate himself if he has to go around finding peoples' faults instead of being a reputable and consistent source of information.
He must really hate himself if he has to go around finding peoples' faults instead of being a reputable and consistent source of information.
08-09-2007, 08:05 PM
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Originally Posted by Tiger2o69
What type of turbo kit and how many lbs are you plan on running?
08-10-2007, 10:16 AM
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I received a call about an issue like this the other day - the vehicle is a FI'd 383 LT1, and when they hit about 5300 RPM it goes lean and throws a MAF Frequency Too High code.
Can this issue be addressed by increasing the MAF size? What if a "bigger" MAF (e.g. from a LS7), was swapped in?
Can this issue be addressed by increasing the MAF size? What if a "bigger" MAF (e.g. from a LS7), was swapped in?
08-10-2007, 12:22 PM
#11
Originally Posted by VinceTrifecta
I received a call about an issue like this the other day - the vehicle is a FI'd 383 LT1, and when they hit about 5300 RPM it goes lean and throws a MAF Frequency Too High code.
Can this issue be addressed by increasing the MAF size? What if a "bigger" MAF (e.g. from a LS7), was swapped in?
Can this issue be addressed by increasing the MAF size? What if a "bigger" MAF (e.g. from a LS7), was swapped in?
thats the real limit.
as far as the MAF freq being too high, you can set the fail frequency higher.. i know some forced induction guys have to do that on here... i havent run into it personally though.
08-12-2007, 01:12 AM
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Originally Posted by My90Iroc
When FI guys max out their maf's does the pcm go right to SD?
Just asking because I was thinking about this since the maf makes for nice driving around and fuel mileage but there are lots of FI cars that max out the maf. What exactly happens from a tuning perspective once the maf is maxed?
Just asking because I was thinking about this since the maf makes for nice driving around and fuel mileage but there are lots of FI cars that max out the maf. What exactly happens from a tuning perspective once the maf is maxed?
08-12-2007, 12:21 PM
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That explains what the shop was seeing that called me the other day - if a FI'd car goes into SD mode when the MAF capacity is exceeded it would go super lean if its a 1bar MAP and/or if it wasn't properly tuned in SD mode (which can't really be done without a >1bar MAP sensor).
I suppose a "safety mechanism" (or perhaps something that resembles a "proper tune") would be to set the PE, open loop AFR and VE tables (if they will accept appropriate values) at the 100 kPa to command the appropriate AFR under full boost. That doesn't address part throttle conditions that might result in the exceeding of the MAF capacity, and manifold pressures above 1 bar - it could cause it to run overly rich because WOT/full boost AFR would be commanded.
So I suppose the answer is either run a big enough MAF, and if you cannot, switch to an SD tune, and if its FI'd, do what is necessary to swap in a >1 bar MAP sensor.
I suppose a "safety mechanism" (or perhaps something that resembles a "proper tune") would be to set the PE, open loop AFR and VE tables (if they will accept appropriate values) at the 100 kPa to command the appropriate AFR under full boost. That doesn't address part throttle conditions that might result in the exceeding of the MAF capacity, and manifold pressures above 1 bar - it could cause it to run overly rich because WOT/full boost AFR would be commanded.
So I suppose the answer is either run a big enough MAF, and if you cannot, switch to an SD tune, and if its FI'd, do what is necessary to swap in a >1 bar MAP sensor.
08-12-2007, 01:10 PM
#14
[QUOTE]MAFs are a crutch used by OEMs to make OE engines maintain themselves within the given EPA guidelines. thats it.
[QUOTE]
It would be interesting to know where you get your information.
Certainly not from the OEMs.
If they are just an emissions crutch, it might make one wonder why many factory race cars have MAFs.
Also, the LS1/LS2 MAF tables are 32 bit values, hence the max hex value is FFFF which is 65535 decimal. It is the way GM scaled the table that makes 512 grams/sec the max value. If you had 8 bit values, with a max of 255, you couldn't have grams/sec values with decimal places, like 60.25, etc. Would have to be incrememts of one gram/sec.
[QUOTE]
It would be interesting to know where you get your information.
Certainly not from the OEMs.
If they are just an emissions crutch, it might make one wonder why many factory race cars have MAFs.
Also, the LS1/LS2 MAF tables are 32 bit values, hence the max hex value is FFFF which is 65535 decimal. It is the way GM scaled the table that makes 512 grams/sec the max value. If you had 8 bit values, with a max of 255, you couldn't have grams/sec values with decimal places, like 60.25, etc. Would have to be incrememts of one gram/sec.
08-12-2007, 01:19 PM
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Also, the LS1/LS2 MAF tables are 32 bit values, hence the max hex value is FFFF which is 65535 decimal. It is the way GM scaled the table that makes 512 grams/sec the max value. If you had 8 bit values, with a max of 255, you couldn't have grams/sec values with decimal places, like 60.25, etc. Would have to be incrememts of one gram/sec.
Ed, does that mean the MAF tables have a resolution of 512/65536? 0xFFFF = 512 g/sec, 0xFFFE = 511.9921874
08-12-2007, 01:30 PM
#16
Yeah, that's what it means...
If the car is supercharged you can tune it on the MAF until the RPM point where the MAF is maxed and then adjust the PE table above that point. It's easy on an SC'd setup since boost is directly tied to RPM and will be the same or lower (belts slip,etc). On a turbo application it gets more sticky since the MAF will max at different points depending on vehicle load.
If the car is supercharged you can tune it on the MAF until the RPM point where the MAF is maxed and then adjust the PE table above that point. It's easy on an SC'd setup since boost is directly tied to RPM and will be the same or lower (belts slip,etc). On a turbo application it gets more sticky since the MAF will max at different points depending on vehicle load.
