How the MAF really works

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Apr 12, 2009 | 07:39 PM

#141

CalEditor

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From: Rock Hill SC

Quote:

Originally Posted by joecar

It's not important.

It doesn't use the MAF at all; from cylinder airmass the PCM computes engine torque which it uses to compute/lookup the trans "throttle signal" pressure (which hydraulically/mechanically modulates line pressure).

I think I would argue that point. Let me get back to my reason later.

Apr 13, 2009 | 09:02 AM

#142

joecar

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From: So.Cal.

Quote:

Originally Posted by CalEditor

I think I would argue that point. Let me get back to my reason later.

Hmmm... good point... maybe I should've said: it uses airmass (to calculate the torque), regardless of where airmass comes from (MAF or VE).

Apr 13, 2009 | 08:36 PM

#143

CalEditor

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From: Rock Hill SC

I have put the question out to several people including John at TC and I haven't heard back. It has been some time so I asked Greg Banish to shed some light on the subject. I guess we will see.

Apr 14, 2009 | 11:06 AM

#144

turbolx

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From: Detroit, Murder City

Quote:

Originally Posted by CalEditor

It has been some time so I asked Greg Banish to shed some light on the subject. I guess we will see.

I already posted earlier in this thread. My position is pretty clear that I think keeping a MAF is a good idea in almost every case. It doesn't necessarily mean using the stock MAF, but one that fits the desired airflow range, resolution and application properly and is properly tuned.

The MAF measurement is one of the most critical to the core function of the PCM. In the absence of the MAF, an airmass estimate is derived from the VE table, measured IAT, rpm, and MAP. But that estimate is only as good as the calibration of the VE table and proper measurements of cylinder air temp and manifold pressure. Sloppy work or bad assumptions in a VE calibration shows up indirectly as poor AFR control, trans performance, idle control and a few other quirks.

Apr 14, 2009 | 11:08 AM

#145

Gh0st

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From: MN

It's funny how some tuners have no idea how the MAF functions yet they claim to know what they're doing.

Apr 14, 2009 | 03:46 PM

#146

joecar

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From: So.Cal.

Well, the MAF measurement is only as good as the MAF table... the argument goes either way... who calibrated either table...?

Is the MAF table a "calibration" or an "estimate"...?
Is the VE table a "calibration" or an "estimate"...?

(which one is more "valid" than the other...?)

Apr 15, 2009 | 12:28 PM

#147

Gh0st

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From: MN

Quote:

Originally Posted by joecar

MAF is a calibration because it's a sensor.

VE is an estimate because it's a predetermined fueling table(which obviously is used in conjuction with many other sources for fueling).

Apr 15, 2009 | 01:04 PM

#148

spaz1

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From: Calgary Ab. Canada

interesting

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Apr 15, 2009 | 08:25 PM

#149

joecar

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From: So.Cal.

Quote:

Originally Posted by Gh0st

MAF is a calibration because it's a sensor.

VE is an estimate because it's a predetermined fueling table(which obviously is used in conjuction with many other sources for fueling).

MAF sensor reports in Hz which the MAF table translates to g/s...

How is this (MAF table lookup) any different than VE table lookup...?

How did GM arrive at the MAF table...?
How did GM arrive at the VE table...?

How can you say that one is better (accurate) compared to the other...?

Apr 15, 2009 | 09:25 PM

#150

Doc

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From: Jacksonville, Fl

Quote:

Originally Posted by joecar

Better?
Yes, quantify?

Total uncertanity of either measurement?

RSS?

Apr 16, 2009 | 07:15 AM

#151

Gh0st

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From: MN

Quote:

Originally Posted by joecar

When you take some time to understand how VE works and how a MAF works your questions will be answered.

Apr 16, 2009 | 09:51 AM

#152

joecar

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From: So.Cal.

Quote:

Originally Posted by Gh0st

When you take some time to understand how VE works and how a MAF works your questions will be answered.

Ok, you explain it to me...

Apr 16, 2009 | 09:56 AM

#153

Gh0st

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From: MN

Quote:

Originally Posted by joecar

Ok, you explain it to me...

Why should I have to do the work for you?

I'd start by reading:

http://redhardsupra.blogspot.com

Specifically: http://redhardsupra.blogspot.com/200...ss-models.html

Additionally you can read Greg Banish's book.

Take the time to educate yourself and don't expect people to just hand you the information with no effort on your part.

BTW, a good tip is to study the tables in your tuning software, they typically explain exactly what the table is referencing and will answer your questions on how the MAF table functions.

Apr 16, 2009 | 10:02 AM

#154

joecar

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From: So.Cal.

Yeah ok I'll do that...

Apr 16, 2009 | 10:12 AM

#155

joecar

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From: So.Cal.

In the meantime, who can answer these questions:

Quote:

MAF sensor reports in frequency which the MAF table translates to airmass flowrate...

How is MAF table lookup any different than VE table lookup...?

How did GM arrive at the MAF table...?
How did GM arrive at the VE table...?

How can one be better compared to the other...?

Apr 16, 2009 | 10:30 AM

#156

Gh0st

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From: MN

Quote:

Originally Posted by joecar

In the meantime, who can answer these questions:

GM didn't arrive at a "MAF table". A MAF is a sensor, Ford uses a MAF exclusively from what I recall and GM used to use SD(case in point my 2002 Cavalier).

I posted the answers to your questions, if you're going to be an *** about it nobody will want to help you.

Apr 16, 2009 | 10:50 AM

#157

joecar

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From: So.Cal.

Quote:

Originally Posted by Gh0st

MAF sensor reports in Hz, PCM converts Hz to g/s by looking up the MAF table, would you agree...?

You didn't answer my questions (you said "Why should I have to do the work for you?")...

and you're missing the whole point of my questions...

and I don't see how I was an ***, would you explain that to me.

Apr 16, 2009 | 12:30 PM

#158

Gh0st

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From: MN

Quote:

Originally Posted by joecar

Yeah ok I'll do that...

Here is where you're being an ***.

When you modify the intake tract you have to also modify the MAF calibration which is the table you see in Hptuners or EFI Live or whatever your tuning suite of choice is.

Apr 16, 2009 | 12:32 PM

#159

turbolx

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From: Detroit, Murder City

Quote:

Originally Posted by joecar

In the meantime, who can answer these questions:
MAF sensor reports in frequency which the MAF table translates to airmass flowrate...

How is MAF table lookup any different than VE table lookup...?

It's just inputs (sensor Hz instead of kPa and RPM) as an input to find a different output (mass flow rate instead of reference pumping efficiency). Both eventually need to be converted into g/cyl numbers for the PCM to calculate a desired fuel mass.

Quote:

How did GM arrive at the MAF table...?

They put the entire air inlet system (silencer, airbox, filter, MAF element, intake tubes, resonators, throttle body, etc.) on a flow bench and take a series of steady state measurements to correlate actual airflow against reported output Hz.

Any time you modify some part of the inlet system (cold air kit, MAF sensor, fileter, etc...), you are changing the relationship between actual airmass and Hz. It may go up or down at any point, but it's different. This is why we need to calibrate this table during the tuning process for modified cars.

Quote:

How did GM arrive at the VE table...?

The perform steady state testing on an engine dyno with everything from the air filter to the tailpipe installed. At each cell in the VE table, they measure actual air and fuel flow along with measured lambda (using an $8000+ ECM dual channel wideband) to determine actual cylinder airmass. This is then converted into VE based on MAP and IAT (thermocouple, not sensor) readings.

Quote:

How can one be better compared to the other...?

Ideally, they should both end up calculating the same cylinder airmass number in steady state. During the transients, we filter the MAF a little more and place more weight on the VE generated number, but the reality is that grams are grams.