My theory of the Maf and its inacuracies (sp)
09-09-2004, 05:26 PM
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My theory of the Maf and its inacuracies (sp) Here is what i think i may stumbled upon with the help of jimmyblue and Another_User
Lately we all have been having problems with the maf skewing trims and such. We have played with the ve table for countless hours to no avail or satisfaction of getting them to where we want them. I think the reason is because (credit to Another_user and Jimmy blue) the lid skews the calibration of the maf by a percentage. I think if there is a 15% change in flow from the lid it may skew the output of the maf to the pcm by that much (this is all dependent on the shape and other things but you get the idea). Here is why i think this
All things being equal with the maf plugged up we have the hardest times situating the trims. Once disconnected everything seems to fall right in line. The difference in trims between the plugged and unplugged should (i feel) be how far out the maf table is. Of course we cant account for all inaccuracies but since the maf table isnt linear (doesnt matter to me) and the curve is hard to re-plot multiplying the maf freq table by a percdntage should get you close to where you want to be( while still keeping the same curve). At this time you can then use the ve table to finish the fine tunning of the trims.
It confused me for a few days how the maf seems to want to fight all the other sensors on the car but when disconnected we see totally opposite behaviours. And I think this is mainly due to a calibration thing.
I also wondered how GM was able to get past this since they obviously calibrated the thing for OUR intakes. I am willing to bet the calibration differes from all vehicles that use the 75mm maf depending on the intake setup. This is one way how they combated different intakes and were able to use the same MAF and keep steady neagtive trim fueling (or close to it)
Feel free to discuss. Hopefully I am not to far off
Lately we all have been having problems with the maf skewing trims and such. We have played with the ve table for countless hours to no avail or satisfaction of getting them to where we want them. I think the reason is because (credit to Another_user and Jimmy blue) the lid skews the calibration of the maf by a percentage. I think if there is a 15% change in flow from the lid it may skew the output of the maf to the pcm by that much (this is all dependent on the shape and other things but you get the idea). Here is why i think this
All things being equal with the maf plugged up we have the hardest times situating the trims. Once disconnected everything seems to fall right in line. The difference in trims between the plugged and unplugged should (i feel) be how far out the maf table is. Of course we cant account for all inaccuracies but since the maf table isnt linear (doesnt matter to me) and the curve is hard to re-plot multiplying the maf freq table by a percdntage should get you close to where you want to be( while still keeping the same curve). At this time you can then use the ve table to finish the fine tunning of the trims.
It confused me for a few days how the maf seems to want to fight all the other sensors on the car but when disconnected we see totally opposite behaviours. And I think this is mainly due to a calibration thing.
I also wondered how GM was able to get past this since they obviously calibrated the thing for OUR intakes. I am willing to bet the calibration differes from all vehicles that use the 75mm maf depending on the intake setup. This is one way how they combated different intakes and were able to use the same MAF and keep steady neagtive trim fueling (or close to it)
Feel free to discuss. Hopefully I am not to far off
09-09-2004, 05:49 PM
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Sure, changes to the intake path would impact the MAF calibration, but I think it would be isolated to pretty low flow situations. It should be pretty accurate once you get a decent amount of air flowing.
Are you talking about low load inaccuracies? What type of flow rates?
I can say this. I have a boosted car and my MAF sits right on top of the intercooler. If that is not a change in the intake path I do not know what is. It still seems pretty darn close to the actual flow in most situations.
I also think having the screen on helps. Things get more intake path specific if you take the screen off. I've seen this really screw up a few cars.
Are you talking about low load inaccuracies? What type of flow rates?
I can say this. I have a boosted car and my MAF sits right on top of the intercooler. If that is not a change in the intake path I do not know what is. It still seems pretty darn close to the actual flow in most situations.
I also think having the screen on helps. Things get more intake path specific if you take the screen off. I've seen this really screw up a few cars.
09-09-2004, 06:07 PM
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I guess low load would be everything below 4k rpm which is where we are seeing most of the issues.
In another thread Ken has informed us that the ve table is ignored over 4000 and the computer is just going off the maf. I guess those are the only times this thing seems to be accraute. If that is the case then i dont think messing with the maf table isnt an option
VE table over 4000 RPM useless with MAF
In another thread Ken has informed us that the ve table is ignored over 4000 and the computer is just going off the maf. I guess those are the only times this thing seems to be accraute. If that is the case then i dont think messing with the maf table isnt an option
VE table over 4000 RPM useless with MAF
09-09-2004, 06:59 PM
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I would think the flow-bias error would be greatest at
high velocities. But you also have to bear in mind that
GM rigged the stock MAF table for the as-built intake
and it could as easily be a problem from -removing-
that ugly piece of upgefukt factory plastic, as anything
being wrong with the aftermarket lids.
I have seen strong movement of low-flow cell LTFTs
with the VE table. I think that's a valid handle for
cells 0-3, 4-5, 8.
The F-body guys (like me) have another problem in
all this, which is the hosed FTC boundaries. Basically
you have one cell (0) that has to cover idle through
Interstate - RPM 0-2500, MAP 0-32. That's going to fit
like crap. Too broad a space, likely conflicting trim
impulses from idle, cruise, light acceleration.
I reset my FTC boundaries to 1000, 2000, 4000RPM;
with my converter and shiftpoints 4000RPM will not
be exceeded until well into the pedal. I set my MAP
boundaries to 40, 60, 80 since I idle with about 30+
kPa and 80+ is pretty much certain to be wide open.
So I lose only one row and one column (or 7 of the
16 cells) to WOT operation and my trimming is more
granular, concentrated where closed loop is meant
to be going on, and nonlinearities in the MAF or the
VE engine characteristics can be compartmentalized
and trimmed to fit, not one-size-fits-all.
4000RPM is also said to be the boundary above which
the MAF is active. Note that with the stock FTC lines,
Cell 1, 5, 9, 13 have to cover the range from 2500 to
6250 (at various MAP levels). This straddles the SD-MAF
cutover and it isn't too surprising that these cells
respond to both MAF and VE tables, and neither of them
completely / satisfactorily.
With the FTC boundaries I use, I saw 1:1 VE:LTFT movement
from table fiddling in the lower cells. Like 1.05X on the table
made -4% - -5% trim drift, and pretty promptly.
You might try this realignment and see if you suddenly get
more trim satisfaction for your tuning action.
high velocities. But you also have to bear in mind that
GM rigged the stock MAF table for the as-built intake
and it could as easily be a problem from -removing-
that ugly piece of upgefukt factory plastic, as anything
being wrong with the aftermarket lids.
I have seen strong movement of low-flow cell LTFTs
with the VE table. I think that's a valid handle for
cells 0-3, 4-5, 8.
The F-body guys (like me) have another problem in
all this, which is the hosed FTC boundaries. Basically
you have one cell (0) that has to cover idle through
Interstate - RPM 0-2500, MAP 0-32. That's going to fit
like crap. Too broad a space, likely conflicting trim
impulses from idle, cruise, light acceleration.
I reset my FTC boundaries to 1000, 2000, 4000RPM;
with my converter and shiftpoints 4000RPM will not
be exceeded until well into the pedal. I set my MAP
boundaries to 40, 60, 80 since I idle with about 30+
kPa and 80+ is pretty much certain to be wide open.
So I lose only one row and one column (or 7 of the
16 cells) to WOT operation and my trimming is more
granular, concentrated where closed loop is meant
to be going on, and nonlinearities in the MAF or the
VE engine characteristics can be compartmentalized
and trimmed to fit, not one-size-fits-all.
4000RPM is also said to be the boundary above which
the MAF is active. Note that with the stock FTC lines,
Cell 1, 5, 9, 13 have to cover the range from 2500 to
6250 (at various MAP levels). This straddles the SD-MAF
cutover and it isn't too surprising that these cells
respond to both MAF and VE tables, and neither of them
completely / satisfactorily.
With the FTC boundaries I use, I saw 1:1 VE:LTFT movement
from table fiddling in the lower cells. Like 1.05X on the table
made -4% - -5% trim drift, and pretty promptly.
You might try this realignment and see if you suddenly get
more trim satisfaction for your tuning action.
09-09-2004, 09:34 PM
#5
Originally Posted by jimmyblue
I reset my FTC boundaries to 1000, 2000, 4000RPM;
with my converter and shiftpoints 4000RPM will not
be exceeded until well into the pedal. I set my MAP
boundaries to 40, 60, 80 since I idle with about 30+
kPa and 80+ is pretty much certain to be wide open.
So I lose only one row and one column (or 7 of the
16 cells) to WOT operation and my trimming is more
granular, concentrated where closed loop is meant
to be going on, and nonlinearities in the MAF or the
VE engine characteristics can be compartmentalized
and trimmed to fit, not one-size-fits-all.
with my converter and shiftpoints 4000RPM will not
be exceeded until well into the pedal. I set my MAP
boundaries to 40, 60, 80 since I idle with about 30+
kPa and 80+ is pretty much certain to be wide open.
So I lose only one row and one column (or 7 of the
16 cells) to WOT operation and my trimming is more
granular, concentrated where closed loop is meant
to be going on, and nonlinearities in the MAF or the
VE engine characteristics can be compartmentalized
and trimmed to fit, not one-size-fits-all.
09-09-2004, 10:30 PM
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Well, I am getting lined up to build my new MAF table. My last run today I was no more than +4, and -3 on my trims. I want to get them all about 0 to -2....if it doesn't work out I can always go back to my last tune I guess. I was really disappointed today...I have an SS roll up next to me, eyeing the car while I am watching my trims...and normally you would hear my Hotcam loping nicely. Instead the darn car runs smooth as silk at idle, so he probably didn't suspect anything (it didn't matter, we were behind cars and couldn't hit it anyways). And this is after I backed my idle down to 900 rpms. Maybe when I am done I will have to go lower, ha ha ha. Nah...900 should be fine. I almost don't want to plug my MAF back in...almost.
I have run into 2 minor issues:
1) It is easier to work on the secondary VE table and then paste back to the primary. Makes tuning go much faster.
2) Pasting back to the primary VE sucks because then you have to fabricate the data in between manually. HP Tuners smoothing can't help me there. I wish I could "lock" cells and then smooth the rest based on the locked cells. That would be excellent (hint, if you guys are reading).
I have run into 2 minor issues:
1) It is easier to work on the secondary VE table and then paste back to the primary. Makes tuning go much faster.
2) Pasting back to the primary VE sucks because then you have to fabricate the data in between manually. HP Tuners smoothing can't help me there. I wish I could "lock" cells and then smooth the rest based on the locked cells. That would be excellent (hint, if you guys are reading).
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09-10-2004, 01:08 AM
#10
maf calibration I'll try to keep the question simple. Since I have a mti lid and removed the mesh screen in the maf, what if anything should I do to the maf calibation tables. for ex: say at 4000hz how much should I increase or decrease the table per frequency, if at all?
Last edited by SmokingWS6; 09-10-2004 at 01:47 AM.
09-10-2004, 01:54 AM
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Originally Posted by SmokingWS6
I'll try to keep the question simple. Since I have an air lid and removed the mesh screen in the maf, what if anything should I do to the maf calibation tables. for ex: say at 4000hz how much should I increase or decrease the table per frequency, if at all?
Removing your MAF screen messing things up because it actually does what it is supposed to do very well. Straighten the air on it's way into the MAF. Since the air is no longer moving straight, any abnormalities in your intake tract will be magnified, messing up the readings even more.
09-10-2004, 10:47 AM
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yes i'd like to see exactly what you changed, and perhaps a brief explanation on how this will enhance normal driving. This data should eventually be collected in a sticky.
Things like VE surging,cold start,ftc optimization, o2 sensor tweaking, ftc etc.
Maybe if i learn this stuff from you guys i'll post a Tuning for dummies faq
p.s. anyone care to email me a stock 2000 Z28 A4 hptuners bin.
Things like VE surging,cold start,ftc optimization, o2 sensor tweaking, ftc etc.
Maybe if i learn this stuff from you guys i'll post a Tuning for dummies faq
p.s. anyone care to email me a stock 2000 Z28 A4 hptuners bin.
09-24-2004, 08:45 AM
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Originally Posted by Slowhawk
Here is something simple I've noticed.A stock MA with the screen is alot more linier to tune in.Most aftermarket and MA's with screens taken out seem to vary run to run.Different air temp with throw off MAF readings as well.
I guess that means scaling the table by 10% should be ok?
