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fomoco74mav
02-03-2013, 11:27 PM
What is this?

RalphP
02-03-2013, 11:43 PM
It's a MAP/BAP sensor (Manifold Absolute Pressure / Barometric Absolute Pressure).

RwP

90sc35thann
02-03-2013, 11:54 PM
It's a MAP/BAP sensor (Manifold Absolute Pressure / Barometric Absolute Pressure).

RwP

On our cars it's a BAP. MAF cars use a BAP and speed-density uses a MAP.

RalphP
02-04-2013, 12:00 AM
Sure! But it's listed as a MAP/BAP sensor.

So I put the whole description there.

RwP

90sc35thann
02-04-2013, 08:30 AM
Sure! But it's listed as a MAP/BAP sensor.

So I put the whole description there.

RwP

It's only a map if it is measuring manifold pressure. Which it is not. In our application it measures barometric pressure.

RalphP
02-04-2013, 09:36 AM
It's only a map if it is measuring manifold pressure. Which it is not. In our application it measures barometric pressure.

But it's the same sensor, doing either duty. It can't do BOTH at the same time, now can it?

In this application, it's a BAP. In others, it may be a MAP.

Did the OP say it was on his SC? No. S/he just asked what it was.

You are making an assumption (which is probably valid, I'll agree!) that it's on a SC. I gave the more complete answer.

BTW - it's never a map, but a MAP. Capitalization is somewhat important, if you're going to be nit picky.

RwP

90sc35thann
02-04-2013, 01:17 PM
But it's the same sensor, doing either duty. It can't do BOTH at the same time, now can it?

In this application, it's a BAP. In others, it may be a MAP.

Did the OP say it was on his SC? No. S/he just asked what it was.

You are making an assumption (which is probably valid, I'll agree!) that it's on a SC. I gave the more complete answer.

BTW - it's never a map, but a MAP. Capitalization is somewhat important, if you're going to be nit picky.

RwP

Clearly from the picture that particular sensor is a BAP and not a MAP. The vacuum port is capped with the standard cap that you would expect to find on a BAP sensor. :-)

Kurt K
02-04-2013, 02:09 PM
To the O.P., I think you got your answer, despite getting blown out of proportion. Hope it helps :rolleyes: :)

90sc35thann
02-04-2013, 02:43 PM
To the O.P., I think you got your answer, despite getting blown out of proportion. Hope it helps :rolleyes: :)

Thanks for moderating :)

A1cntrler
02-04-2013, 03:21 PM
But what does it do? If it measures barometric pressure, I would assume that it measures the density of the air and adjusts accordingly the fuel mixture to compensate for changes in elevation and such?

90sc35thann
02-04-2013, 05:49 PM
But what does it do? If it measures barometric pressure, I would assume that it measures the density of the air and adjusts accordingly the fuel mixture to compensate for changes in elevation and such?

It doesn't measure air density. It measures barometric pressure. The MAF measures air density. Oddly I remember reading somewhere that it only measures the barometric pressure once per start up. I am not certain of this fact. I'll bet the folks on here running the quarterhorse can tell you if they have seen dynamic ranges for the BAP while data logging. Folks?

S_Mazza
02-04-2013, 06:05 PM
It doesn't measure air density. It measures barometric pressure. The MAF measures air density. Oddly I remember reading somewhere that it only measures the barometric pressure once per start up. I am not certain of this fact. I'll bet the folks on here running the quarterhorse can tell you if they have seen dynamic ranges for the BAP while data logging. Folks?

The MAF doesn't measure density because it has no way of knowing volumetric flow rate. All it does is estimate the total mass of air flowing past it. I believe that a density calculation must be done in the EEC.

As for the pressure reading, I believe that applied to the Ford cars with a MAP sensor. (As mentioned before, it's the exact same sensor but with a pipe leading to the manifold instead of just a capped port.) There's no way to get barometric pressure from the manifold of a running vehicle, so it measures at key-on, before engine start. I think it may also take a reference measurement at WOT conditions (since it would in theory mean 0 vacuum), but realistically, there is restriction in the intake tract, so it would still not be a true barometric reading.

bowez
02-04-2013, 06:29 PM
Straight form Ford 93/94 EVTM


The Barometric Pressure (BARO) sensor (Figure 1) measures barometric pressure using a frequency. This gives the Powertrain Control Module (PCM) information on engine load or air density.

It is used as a barometric sensor for altitude compensation, updating the PCM during Key On, Engine Off and every wide-open throttle.

The PCM uses BARO for:

l Spark advance

l EGR flow

l Air/fuel ratio


Description

The Manifold Absolute Pressure (MAP) sensor (Figure 13) measures manifold vacuum using a frequency. This gives the Powertrain Control Module (PCM) information on engine load.

It is used as a barometric sensor for altitude compensation, updating the PCM during Key On, Engine Off and every wide-open throttle.

The PCM uses MAP for:

l Spark advance

l EGR flow

l Air/fuel ratio

Either way Ford figured out it wasn't needed. MAF can do it function.

90sc35thann
02-04-2013, 08:24 PM
The MAF doesn't measure density because it has no way of knowing volumetric flow rate. All it does is estimate the total mass of air flowing past it. I believe that a density calculation must be done in the EEC.

As for the pressure reading, I believe that applied to the Ford cars with a MAP sensor. (As mentioned before, it's the exact same sensor but with a pipe leading to the manifold instead of just a capped port.) There's no way to get barometric pressure from the manifold of a running vehicle, so it measures at key-on, before engine start. I think it may also take a reference measurement at WOT conditions (since it would in theory mean 0 vacuum), but realistically, there is restriction in the intake tract, so it would still not be a true barometric reading.
Correct it does measure mass but it does compensate for density as mass will change with density, no?

S_Mazza
02-04-2013, 09:21 PM
Correct it does measure mass but it does compensate for density as mass will change with density, no?

Yes, but mass also changes with volume flow increase or decrease. I am just saying that the EEC needs additional info to get density information. The MAF does not provide enough information on its own.

For example, you could calculate air density by reading the measured mass flow rate, reading the tach RPM signal and throttle position, using pre-determined values for volumetric efficiency under those engine operating parameters, and calculating the air density, then checking the air-fuel readings of the O2 sensor against the calculated / expected air-fuel ratio.

But that's a bit involved, you know?

I wonder if Ford didn't make a smart move by using the BAP to bypass all those calculations at a time (1980s) when processing power was expensive, but then in later generations, they realized that it was cheaper to use brute force computation, rather than pay for the additional sensor.

90sc35thann
02-04-2013, 09:34 PM
Yes, but mass also changes with volume flow increase or decrease. I am just saying that the EEC needs additional info to get density information. The MAF does not provide enough information on its own.

For example, you could calculate air density by reading the measured mass flow rate, reading the tach RPM signal and throttle position, using pre-determined values for volumetric efficiency under those engine operating parameters, and calculating the air density, then checking the air-fuel readings of the O2 sensor against the calculated / expected air-fuel ratio.

But that's a bit involved, you know?

I wonder if Ford didn't make a smart move by using the BAP to bypass all those calculations at a time (1980s) when processing power was expensive, but then in later generations, they realized that it was cheaper to use brute force computation, rather than pay for the additional sensor.


That makes sense and your explanation was easy to understand. Thanks man!

RalphP
02-04-2013, 10:39 PM
Actually, according to Greg Banish in his EFI manual - the tables used by the ECU took no more to build than with speed density, and make a much more linear airflow/injector curve than using a BAP or MAP to compute the absolute or manifold pressure (for speed density) and working off the lookup table.

RwP

S_Mazza
02-05-2013, 12:41 PM
That makes sense and your explanation was easy to understand. Thanks man!

No problem.


Actually, according to Greg Banish in his EFI manual - the tables used by the ECU took no more to build than with speed density, and make a much more linear airflow/injector curve than using a BAP or MAP to compute the absolute or manifold pressure (for speed density) and working off the lookup table.

RwP

Hmm. I haven't read that book. Which system is he referring to? The one in the current Ford cars (2013)? Or the one in our cars?