Adjusting MAF question.
10-05-2010, 09:46 PM
#1
Adjusting MAF question. The MAF is read in Hz. so lets say at 3500rpms im reading 9000 Hz and my a/f is 12.0:1 , and at 4500rpms it also reads 9000 Hz but the a/f is 12.8:1
How do you adjust the MAF in correlation to the RPM and a/f ?
What ive done so far:
99 vette 6spd, 224R cam, ported stock heads, headers, 42# injectors, 93 octane gas.
1. Scaled injectors.
2. Tuned in SD , VE tables, Idle air, Idle/cruise- 14.5:1, Mid range RPM 12.3-12.5:1, and higher rpms its at about 12.9-13.0:1...ran like a champ.
3. Set back to read MAF, all a/f's dropped about 1 whole number.
4. Multiplied MAF table by .95 , idle and cruise came back to normal, mid and upper bounce back and fourth, I cant have good mid and upper at the same time, its either one or the other.
How do you adjust the MAF in correlation to the RPM and a/f ?
What ive done so far:
99 vette 6spd, 224R cam, ported stock heads, headers, 42# injectors, 93 octane gas.
1. Scaled injectors.
2. Tuned in SD , VE tables, Idle air, Idle/cruise- 14.5:1, Mid range RPM 12.3-12.5:1, and higher rpms its at about 12.9-13.0:1...ran like a champ.
3. Set back to read MAF, all a/f's dropped about 1 whole number.
4. Multiplied MAF table by .95 , idle and cruise came back to normal, mid and upper bounce back and fourth, I cant have good mid and upper at the same time, its either one or the other.
10-05-2010, 10:57 PM
#2
The MAF literally measures airflow, so you are at the same volume of air in both places for the frequency to be the same. If you look at the two in the log, the different MAP values at the two points where the MAF reads the same are the give away to relative load.
The MAF is the easy part. Log MAF freq. Make a histogram that uses the MAF's table and log AFR % error into the histogram table. It's like the VE process with one less dimension. Use your head to weed out bad and transitional data as well as the filters in the histo.
The MAF is the easy part. Log MAF freq. Make a histogram that uses the MAF's table and log AFR % error into the histogram table. It's like the VE process with one less dimension. Use your head to weed out bad and transitional data as well as the filters in the histo.
10-06-2010, 07:46 AM
#3
The MAF literally measures airflow, so you are at the same volume of air in both places for the frequency to be the same. If you look at the two in the log, the different MAP values at the two points where the MAF reads the same are the give away to relative load.
The MAF is the easy part. Log MAF freq. Make a histogram that uses the MAF's table and log AFR % error into the histogram table. It's like the VE process with one less dimension. Use your head to weed out bad and transitional data as well as the filters in the histo.
The MAF is the easy part. Log MAF freq. Make a histogram that uses the MAF's table and log AFR % error into the histogram table. It's like the VE process with one less dimension. Use your head to weed out bad and transitional data as well as the filters in the histo.
10-06-2010, 08:12 AM
#4
The MAF measures airflow only, it does not care about rpm.
If you have some rolling hills, set your cruise control at a fixed speed & watch how many different MAF cells you hit.
You can do the same thing on a load bearing dyno, set the dyno to hold a certain rpm or mph. Now you move your throttle from whatever position to hold the selected load to WOT, watch your MAF & see the number of cells you hit.
Are you MAF only when you calibrating those tables?
If you have some rolling hills, set your cruise control at a fixed speed & watch how many different MAF cells you hit.
You can do the same thing on a load bearing dyno, set the dyno to hold a certain rpm or mph. Now you move your throttle from whatever position to hold the selected load to WOT, watch your MAF & see the number of cells you hit.
Are you MAF only when you calibrating those tables?
10-06-2010, 10:53 AM
#5
Moderator
iTrader: (11)
Join Date: Mar 2002
Location: East Central Florida
Posts: 12,604
Likes: 0
Received 6 Likes
on
6 Posts
You have a MAF table that maps Hz to g/sec airflow.
That is best left alone if you have a stock intake tract
and a stock MAF, the calibration from the factory is
at least based on some engineering.
All you should ask from a sensor is accuracy. You would
like to separate fact from intention, air error from fuel
delivery error and so on and for each, fix the appropriate
source.
VE tuning, when you have fuel errors present, embeds those
errors to the VE table. This could be one reason why your
MAF now disagrees. But is it really wrong?
On the other hand, particularly at low RPM, reversion pulses
from a bigger cam can make airflow "double-sample" and
raise the MAF reading. This, the MAF table would be a
reasonable place to fix.
You can find some variation in vehicle platform MAF tables
for the same Delphi piece, indicating that intake lineup
changes can matter to MAF fidelity. Few-% range, but
1% is 0.15 AFR points.
That is best left alone if you have a stock intake tract
and a stock MAF, the calibration from the factory is
at least based on some engineering.
All you should ask from a sensor is accuracy. You would
like to separate fact from intention, air error from fuel
delivery error and so on and for each, fix the appropriate
source.
VE tuning, when you have fuel errors present, embeds those
errors to the VE table. This could be one reason why your
MAF now disagrees. But is it really wrong?
On the other hand, particularly at low RPM, reversion pulses
from a bigger cam can make airflow "double-sample" and
raise the MAF reading. This, the MAF table would be a
reasonable place to fix.
You can find some variation in vehicle platform MAF tables
for the same Delphi piece, indicating that intake lineup
changes can matter to MAF fidelity. Few-% range, but
1% is 0.15 AFR points.
10-06-2010, 02:29 PM
#6
You have a MAF table that maps Hz to g/sec airflow.
That is best left alone if you have a stock intake tract
and a stock MAF, the calibration from the factory is
at least based on some engineering.
All you should ask from a sensor is accuracy. You would
like to separate fact from intention, air error from fuel
delivery error and so on and for each, fix the appropriate
source.
VE tuning, when you have fuel errors present, embeds those
errors to the VE table. This could be one reason why your
MAF now disagrees. But is it really wrong?
On the other hand, particularly at low RPM, reversion pulses
from a bigger cam can make airflow "double-sample" and
raise the MAF reading. This, the MAF table would be a
reasonable place to fix.
You can find some variation in vehicle platform MAF tables
for the same Delphi piece, indicating that intake lineup
changes can matter to MAF fidelity. Few-% range, but
1% is 0.15 AFR points.
That is best left alone if you have a stock intake tract
and a stock MAF, the calibration from the factory is
at least based on some engineering.
All you should ask from a sensor is accuracy. You would
like to separate fact from intention, air error from fuel
delivery error and so on and for each, fix the appropriate
source.
VE tuning, when you have fuel errors present, embeds those
errors to the VE table. This could be one reason why your
MAF now disagrees. But is it really wrong?
On the other hand, particularly at low RPM, reversion pulses
from a bigger cam can make airflow "double-sample" and
raise the MAF reading. This, the MAF table would be a
reasonable place to fix.
You can find some variation in vehicle platform MAF tables
for the same Delphi piece, indicating that intake lineup
changes can matter to MAF fidelity. Few-% range, but
1% is 0.15 AFR points.
Trending Topics
10-06-2010, 03:13 PM
#8
Moderator
iTrader: (11)
Join Date: Mar 2002
Location: East Central Florida
Posts: 12,604
Likes: 0
Received 6 Likes
on
6 Posts
How does one find the appropriate source?
Easier if you are methodical and change one thing at a time.
I have gotten pretty suspicious of the fueling model, that
it presumes a fixed and consistent head pressure value
at the rails. But we all know this is untrue. And if you look
at the IFR table, it seems to be based on ideality vs MAP
with nothing for RPM, so no fuel fade figuring. Yet I see
more than the 58PSI at idle (so low-fueling is bent high,
which would make me jack the VE lower than real to
compensate) and down to 52PSI at the big end (so fake
the VE higher than realistic, there). This all, you'd ideally
fix with a manifold referenced return regulator up by the
rail so pressure is know a "known", not an assumption.
But few people consider this, and fewer would want to
simply for the sake of fidelity.
But the problem with tuning around nonidealities is, they
accumulate.
It's a real exercise, figuring out all the ways that things
are not as they seem, or are assumed to be. Sometimes
it is easier, and good enough, to just get to the "right
result". But then you go and remove one existing piece
of wrongness and it all goes a skosh sideways when you
thought it was right and tight.
10-06-2010, 03:44 PM
#9
Yes.
Thanks, I'll just have to mess w/ it some more and see.
That is indeed the nut of it.
Easier if you are methodical and change one thing at a time.
I have gotten pretty suspicious of the fueling model, that
it presumes a fixed and consistent head pressure value
at the rails. But we all know this is untrue. And if you look
at the IFR table, it seems to be based on ideality vs MAP
with nothing for RPM, so no fuel fade figuring. Yet I see
more than the 58PSI at idle (so low-fueling is bent high,
which would make me jack the VE lower than real to
compensate) and down to 52PSI at the big end (so fake
the VE higher than realistic, there). This all, you'd ideally
fix with a manifold referenced return regulator up by the
rail so pressure is know a "known", not an assumption.
But few people consider this, and fewer would want to
simply for the sake of fidelity.
But the problem with tuning around nonidealities is, they
accumulate.
It's a real exercise, figuring out all the ways that things
are not as they seem, or are assumed to be. Sometimes
it is easier, and good enough, to just get to the "right
result". But then you go and remove one existing piece
of wrongness and it all goes a skosh sideways when you
thought it was right and tight.
Easier if you are methodical and change one thing at a time.
I have gotten pretty suspicious of the fueling model, that
it presumes a fixed and consistent head pressure value
at the rails. But we all know this is untrue. And if you look
at the IFR table, it seems to be based on ideality vs MAP
with nothing for RPM, so no fuel fade figuring. Yet I see
more than the 58PSI at idle (so low-fueling is bent high,
which would make me jack the VE lower than real to
compensate) and down to 52PSI at the big end (so fake
the VE higher than realistic, there). This all, you'd ideally
fix with a manifold referenced return regulator up by the
rail so pressure is know a "known", not an assumption.
But few people consider this, and fewer would want to
simply for the sake of fidelity.
But the problem with tuning around nonidealities is, they
accumulate.
It's a real exercise, figuring out all the ways that things
are not as they seem, or are assumed to be. Sometimes
it is easier, and good enough, to just get to the "right
result". But then you go and remove one existing piece
of wrongness and it all goes a skosh sideways when you
thought it was right and tight.
