MAF table adjustment for Ported MAF
08-28-2006, 02:41 AM
#1
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Thread Starter
Join Date: Jan 2000
Location: Calgary, Ab, Canada
Posts: 731
MAF table adjustment for Ported MAF
Hey guys,
I have a ported MAF (spare one) I'd like to try on my '95 LT1. Am wondering what should be done to the MAF tables to compensate for that. My MAF is WELL ported.
I did some searching, and I've heard of guys saying not to use ported MAFs. Is this so, and if so, why not? I have a predator hood with the ram air intake setup, so straight (no elbows) pre and post MAF.
If I use my stock ported MAF, what should I do to the MAF tables? What about the Air/fuel ratio?
If I use the stock untouched MAF, what should I do to both?
I advanced the timing by 1 deg. accross the board.
Car has full boltons basically. Longtubes, ORY, catback, elect wp, roller rockers, airfoil, 4.10s, MSD opti and plugs/wires and free mods.
Thanks.
I have a ported MAF (spare one) I'd like to try on my '95 LT1. Am wondering what should be done to the MAF tables to compensate for that. My MAF is WELL ported.
I did some searching, and I've heard of guys saying not to use ported MAFs. Is this so, and if so, why not? I have a predator hood with the ram air intake setup, so straight (no elbows) pre and post MAF.
If I use my stock ported MAF, what should I do to the MAF tables? What about the Air/fuel ratio?
If I use the stock untouched MAF, what should I do to both?
I advanced the timing by 1 deg. accross the board.
Car has full boltons basically. Longtubes, ORY, catback, elect wp, roller rockers, airfoil, 4.10s, MSD opti and plugs/wires and free mods.
Thanks.
Last edited by IgorT.455/406; 08-28-2006 at 03:02 AM.
08-28-2006, 01:28 PM
#2
Registered User
Join Date: Apr 2006
Location: Lancashire UK
Posts: 58
Re: MAF table adjustment for Ported MAF
Most will say don't do it, it's long winded rather than difficult.
It only took 3-4 data runs to do it but the calcs a little harder.
Calc, for each AFGS table entry, the avg BLM %age.(Left and Right)throughout your data run, adjust that table by your final figure.
Remember,
a Positive BLM %ge means LEAN (PCM adding fuel)... make maf entry bigger */
a NEGative BLM %ge means RICH (PCM pulling fuel)... make maf entry smaller */
Mine adjusted 16% at the bottom to 0 at around 8500
WhatI have noticed is that the actual AFGS values seem fairly consistent.. ie they actually drop around 1-2 grams down the table.
My feeling on this is that the MAF is just out by a few grams that it isn't seeing properly.
I've not altered any tables over 8500 as the mis represented air flow seems negligable by then.
I did write software to calc this, but it's a bit confusing.
If you get stuck, contact me.
HTH
Mitch
Maybe I should look at this software again or write up on my website.
It only took 3-4 data runs to do it but the calcs a little harder.
Calc, for each AFGS table entry, the avg BLM %age.(Left and Right)throughout your data run, adjust that table by your final figure.
Remember,
a Positive BLM %ge means LEAN (PCM adding fuel)... make maf entry bigger */
a NEGative BLM %ge means RICH (PCM pulling fuel)... make maf entry smaller */
Mine adjusted 16% at the bottom to 0 at around 8500
WhatI have noticed is that the actual AFGS values seem fairly consistent.. ie they actually drop around 1-2 grams down the table.
My feeling on this is that the MAF is just out by a few grams that it isn't seeing properly.
I've not altered any tables over 8500 as the mis represented air flow seems negligable by then.
I did write software to calc this, but it's a bit confusing.
If you get stuck, contact me.
HTH
Mitch
Maybe I should look at this software again or write up on my website.
08-28-2006, 02:41 PM
#3
Registered User
Thread Starter
Join Date: Jan 2000
Location: Calgary, Ab, Canada
Posts: 731
Re: MAF table adjustment for Ported MAF
Thanks!
Do you know if there is any online articles and good reading on novice tuners. Basically I have knowledge of how some stuff works, but am pretty new to EFI and would like to learn how to tune my car and understand the stuff.
Thanks,
Igor.
Do you know if there is any online articles and good reading on novice tuners. Basically I have knowledge of how some stuff works, but am pretty new to EFI and would like to learn how to tune my car and understand the stuff.
Thanks,
Igor.
08-28-2006, 04:03 PM
#4
Registered User
Join Date: Nov 2000
Location: Ft. Worth, TX
Posts: 1,937
Re: MAF table adjustment for Ported MAF
I learned alot about this topic when I had a TPI via this board and posts:
http://www.thirdgen.org/techboard/diy-prom/
Same principals apply to LT1s.
To "perfect" the MAF tables, take a data logger, such as Data Master, and cruise around getting about 20 secs of data at different MAF AFG readings, 15, 20, 25, 30..etc up to a high as you can without going too fast
Then review the recording and noting the BLMs at each MAF reading and whether or not the Short Term Int are still changing rapidly at the end of each 20 sec interval.
Then you adjust the MAF table for each of those MAF reading intervals using the BLM you recorded for it and "fill in the gaps" in between each interval...
So for example...at 20 AFGS, your BLMs were steady at 120...thats 7% below 128...you need to lean out the MAF calc by 7% at 20 AFGS.
The MAF table is actually a conversion between frequencies that the MAF reads and converts that to the AFGS.
So at whatever Hz equals 20 AFGS in the MAF table, you need to reduce the 20 AFGS by 7% (mutiply 20 * .93) and that the new AGFS number to put in the MAF table were at did read 20.
Do the same calc for the AFGS number below and above 20 to the "next" interval you recorded..such as 25 AFGS...
It's very time consuming and tedious, but once you get the hang of it, you can do one in about 2 rounds of make the calcs..go back and reflash ..drive around and do it again...2 rounds will have you very close to a perfect 128 BLM everywhere... I try to target 126-134 BLMs.
Some say why bother if the PCM can still control the AF, but sometimes there will be a wide BLM change in a single Fuel Trim cell for the same rpm but different load and it will take the computer sometimes 10-15 seconds to trim or add enough fuel and you can feel the differeence driving until the correct AF is achieved in that same fuel trim cell.
Mine was lean at idle, but as soon as the pedal was touched it would go instantly rich..making the engine almost bog because the BLMS would go from 140 to 115 in the SAME fuel trim cell.
http://www.thirdgen.org/techboard/diy-prom/
Same principals apply to LT1s.
To "perfect" the MAF tables, take a data logger, such as Data Master, and cruise around getting about 20 secs of data at different MAF AFG readings, 15, 20, 25, 30..etc up to a high as you can without going too fast
Then review the recording and noting the BLMs at each MAF reading and whether or not the Short Term Int are still changing rapidly at the end of each 20 sec interval.
Then you adjust the MAF table for each of those MAF reading intervals using the BLM you recorded for it and "fill in the gaps" in between each interval...
So for example...at 20 AFGS, your BLMs were steady at 120...thats 7% below 128...you need to lean out the MAF calc by 7% at 20 AFGS.
The MAF table is actually a conversion between frequencies that the MAF reads and converts that to the AFGS.
So at whatever Hz equals 20 AFGS in the MAF table, you need to reduce the 20 AFGS by 7% (mutiply 20 * .93) and that the new AGFS number to put in the MAF table were at did read 20.
Do the same calc for the AFGS number below and above 20 to the "next" interval you recorded..such as 25 AFGS...
It's very time consuming and tedious, but once you get the hang of it, you can do one in about 2 rounds of make the calcs..go back and reflash ..drive around and do it again...2 rounds will have you very close to a perfect 128 BLM everywhere... I try to target 126-134 BLMs.
Some say why bother if the PCM can still control the AF, but sometimes there will be a wide BLM change in a single Fuel Trim cell for the same rpm but different load and it will take the computer sometimes 10-15 seconds to trim or add enough fuel and you can feel the differeence driving until the correct AF is achieved in that same fuel trim cell.
Mine was lean at idle, but as soon as the pedal was touched it would go instantly rich..making the engine almost bog because the BLMS would go from 140 to 115 in the SAME fuel trim cell.
08-30-2006, 05:29 PM
#5
Registered User
Join Date: Dec 2001
Location: winnipeg
Posts: 275
Re: MAF table adjustment for Ported MAF
im using ported maf ends on my cammed ls1. i just tuned it right on the dyno. my a\f's are right where i wanna be. if i went back to the stock maf ends ( people have told me to do it to help my idle problem) would it mess up my a\f's?
07-31-2007, 12:06 PM
#6
Registered User
Join Date: Oct 2006
Location: La.
Posts: 270
I learned alot about this topic when I had a TPI via this board and posts:
http://www.thirdgen.org/techboard/diy-prom/
Same principals apply to LT1s.
To "perfect" the MAF tables, take a data logger, such as Data Master, and cruise around getting about 20 secs of data at different MAF AFG readings, 15, 20, 25, 30..etc up to a high as you can without going too fast
Then review the recording and noting the BLMs at each MAF reading and whether or not the Short Term Int are still changing rapidly at the end of each 20 sec interval.
Then you adjust the MAF table for each of those MAF reading intervals using the BLM you recorded for it and "fill in the gaps" in between each interval...
So for example...at 20 AFGS, your BLMs were steady at 120...thats 7% below 128...you need to lean out the MAF calc by 7% at 20 AFGS.
The MAF table is actually a conversion between frequencies that the MAF reads and converts that to the AFGS.
So at whatever Hz equals 20 AFGS in the MAF table, you need to reduce the 20 AFGS by 7% (mutiply 20 * .93) and that the new AGFS number to put in the MAF table were at did read 20.
Do the same calc for the AFGS number below and above 20 to the "next" interval you recorded..such as 25 AFGS...
It's very time consuming and tedious, but once you get the hang of it, you can do one in about 2 rounds of make the calcs..go back and reflash ..drive around and do it again...2 rounds will have you very close to a perfect 128 BLM everywhere... I try to target 126-134 BLMs.
Some say why bother if the PCM can still control the AF, but sometimes there will be a wide BLM change in a single Fuel Trim cell for the same rpm but different load and it will take the computer sometimes 10-15 seconds to trim or add enough fuel and you can feel the differeence driving until the correct AF is achieved in that same fuel trim cell.
Mine was lean at idle, but as soon as the pedal was touched it would go instantly rich..making the engine almost bog because the BLMS would go from 140 to 115 in the SAME fuel trim cell.
http://www.thirdgen.org/techboard/diy-prom/
Same principals apply to LT1s.
To "perfect" the MAF tables, take a data logger, such as Data Master, and cruise around getting about 20 secs of data at different MAF AFG readings, 15, 20, 25, 30..etc up to a high as you can without going too fast
Then review the recording and noting the BLMs at each MAF reading and whether or not the Short Term Int are still changing rapidly at the end of each 20 sec interval.
Then you adjust the MAF table for each of those MAF reading intervals using the BLM you recorded for it and "fill in the gaps" in between each interval...
So for example...at 20 AFGS, your BLMs were steady at 120...thats 7% below 128...you need to lean out the MAF calc by 7% at 20 AFGS.
The MAF table is actually a conversion between frequencies that the MAF reads and converts that to the AFGS.
So at whatever Hz equals 20 AFGS in the MAF table, you need to reduce the 20 AFGS by 7% (mutiply 20 * .93) and that the new AGFS number to put in the MAF table were at did read 20.
Do the same calc for the AFGS number below and above 20 to the "next" interval you recorded..such as 25 AFGS...
It's very time consuming and tedious, but once you get the hang of it, you can do one in about 2 rounds of make the calcs..go back and reflash ..drive around and do it again...2 rounds will have you very close to a perfect 128 BLM everywhere... I try to target 126-134 BLMs.
Some say why bother if the PCM can still control the AF, but sometimes there will be a wide BLM change in a single Fuel Trim cell for the same rpm but different load and it will take the computer sometimes 10-15 seconds to trim or add enough fuel and you can feel the differeence driving until the correct AF is achieved in that same fuel trim cell.
Mine was lean at idle, but as soon as the pedal was touched it would go instantly rich..making the engine almost bog because the BLMS would go from 140 to 115 in the SAME fuel trim cell.
Thanks
07-31-2007, 06:22 PM
#7
Registered User
Join Date: Jun 2003
Location: Saginaw, Michigan
Posts: 3,620
It won't mess up the partial throttle, as long as your computer has enough range to adjust the a/f to 14.7 like it wants.
You may have problems with WOT running rich if your stock MAF readings are making the car run in a lean condition(PCM adding fuel to compensate) before you hit WOT. In that case, the PCM uses the power enrichment(WOT) tables, in addition to how much the computer was adding fuel right before WOT was entered.
I hope that makes sense.
Dan
You may have problems with WOT running rich if your stock MAF readings are making the car run in a lean condition(PCM adding fuel to compensate) before you hit WOT. In that case, the PCM uses the power enrichment(WOT) tables, in addition to how much the computer was adding fuel right before WOT was entered.
I hope that makes sense.
Dan
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