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Discussion Starter #1
So ford and all the other have used maf , map, separately and together for engine management. maf tells the eec what coming and map tells it's there. Both work well together and separate. Why didn't they use a differential pressure transmitter across the throttle body as well? Just my 2cents
 

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Well the question is, what problem is that solving? If SD or MAF can put you on a mixture target, what more is needed?
 

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The maf tells you kg/hr in front of the T.B. The BAP tells you pressure / vacuum behind the T.B. Correct.

So why does ford and GM use both?

I understand either will both will aid in fueling.

Why would D.P. help. If the T.B is closed the motor is in vacuum. Correct?Atmospheric conditions will differ. Use a BAP sensor with the known engines demands. What happens. You tell me.
 

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MAF tells you both actually. The fluid moves as a column, it isn't getting past the MAF unless it's moving into the cylinders. It doesn't matter what is in between. As long as the system is sealed up tight, there's nothing you can do to make the MAF measurement not represent the cylinder fill which means there is no other measurement you can make to enrich the data further.

A MAP based strategy does need to know the differential but it doesn't need to be exactly at the T.B. Typically it will either use a MAP from the manifold plus a BAP from the engine compartment, or it will use the MAP at key on before the engine starts to take a one-time BAP reading and assume that reading doesn't change much thereafter. This is normally fine but can cause problems if you're going up or down a mountain.
 

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The maf tells you kg/hr in front of the T.B. The BAP tells you pressure / vacuum behind the T.B. Correct.

So why does ford and GM use both?

I understand either will both will aid in fueling.

Why would D.P. help. If the T.B is closed the motor is in vacuum. Correct?Atmospheric conditions will differ. Use a BAP sensor with the known engines demands. What happens. You tell me.
first you need to know, absolute pressure is used, NOT gauge

manifold is pressure, not vacuum

second, fuel is delivered by mass, by the correlating measured or calculated air mass

why are both maf and map used in some applications? really that is something that oems developed from some need, be it mileage or emissions constraints
 

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Discussion Starter #7
Maf measurers what? weight right

bap logs what. pressure right. so there is no vacuum with your statement. So there is still a differential in pressure. Right.

Please explain
 

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MAF is measuring the mass. The volume is fixed. Pressure is just how much mass vs. that fixed volume. Using pressure and temperature is a way to derive the mass of air based on the known volume via Boyle's law.

Using a MAF you simply measure the mass directly. With MAF you don't even need the temperature because the measured mass is absolute. As the gas temperature rises reducing mass, the MAF will directly read that reduced mass.

The pressure delta across the throttle body, or across any other point along the intake is irrelevant. The only thing that matters is the air mass entering the cylinder, because that is the air mass you are mixing with your fuel mass.

The circumstance where you care about the pressure delta is trying to determine how much resistance there is to the air column moving at that point, but measuring what it is doesn't actually tell you anything about the air mass at that point unless you know some other data as well. If you get all that other data you're just reinventing speed density but measuring vacuum at a different location. There isn't anything special about the location.
 

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Maf measurers what? weight right

bap logs what. pressure right. so there is no vacuum with your statement. So there is still a differential in pressure. Right.

Please explain
what do you want to be explained?

maf is a measure of MASS AIR FLOW

the ecm, delivers, MASS FUEL FLOW
 

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Discussion Starter #10
Thanks Seijirou.

So GM uses SD and MAF on some models. Do they use a BAP. If so why. Which one controls what?.
 

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Sorry I'm not familiar with the GM strategies so I can't really comment on that. Both are capable of doing everything needed but they might like the characteristics of one over the other for some things. Perhaps they find that acceleration enrichment works better with manifold vacuum in the solution. It could simply be another data point for more accurate self diagnostics.
 

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...So GM uses SD and MAF on some models. Do they use a BAP. If so why. Which one controls what?.
Everything they do is to meet federal gov't emissions requirements.
Fuel economy & performance are secondary.

Some manufacturers have eliminated the MAF on some models, probably due to cost, it being more expensive than MAP or BAP sensors.
 
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GM blends MAF with MAP to have a better predicted VE. Most GM tunes stock use MAF only at 4,000+ RPM since MAF measures actual airmass its more accurate and can compensate for any performance improvements or diminishes that would cause lean out or enrichment since speed density can only deliver x amount of fuel at 0 vac / 0 boost.

Simply put, in order to have accurate fuel control you have to calculate an accurate airmass. The rest is simple math i.e. x airmass * y(air fuel ratio) = x:y Air fuel ratio.

MAF gives more accurate fuel control since your measuring the actual airmass.

AM = Actual AM from MAF Sensor

Speed density (MAP) you are assuming at a given RPM and pressure that in order to achieve x:y ratio you MUST be inhaling x amount of air its simply guess work and assumes airmass doesn't change for a given condition (rpm and pressure) which is defined in the VE table.

therefore simply put,
AM = Looked up AM from VE table
 

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I didn't say it directly earlier but I figured they used MAP because it responds more quickly to transients than the MAF meter hanging off the periphery. This would be more prominent at lower RPM (so it kind of jives that they don't use it at 4,000+ RPM like Decipha pointed out). I'm inferring then that there's an economy gain in that response time, which is to Indy's point. That's completely conjecture though and I don't know it to be true.

Also I believe at least some of the current Ford Ecoboosts are strictly MAP.
 

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With Megasquirt & a MAF, VE table is only used for trim. It actually makes it a bit easier to understand, since VE table starts at 100 for all cells, i.e. 100%. You then increase or decrease cell depending on the volumetric efficiency for that cell condition (load vs. rpm).
 

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So is SD preferred over MAF for turbo application?
When the amount of air required to make power is limited by the MAF meter, it is time to go SD
 
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