Barometric pressure sensor.

[K4fxd]

I was doing some logs and noticed with the engine off my scanner shows a baro reading from the car as 13.2 PSI and the manifold pressure as 101 KPA. These numbers are way off.

101 KPA = 14.65 PSI

Is there a baro sensor on the 17 mustang GT? Google is not turning anything up.

Thanks

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[markmurfie]

I was doing some logs and noticed with the engine off my scanner shows a baro reading from the car as 13.2 PSI and the manifold pressure as 101 KPA. These numbers are way off.

101 KPA = 14.65 PSI

Is there a baro sensor on the 17 mustang GT? Google is not turning anything up.

Thanks

No.

There's not a manifold pressure sensor either,unless you are looking at one you installed.

 

[K4fxd]

Where are these numbers coming from? My histogram shows spark advance against manifold absolute pressure.

I'm confused.

 

[markmurfie]

Where are these numbers coming from? My histogram shows spark advance against manifold absolute pressure.

I'm confused.

The mass airflow sensor gives how much airmass is getting into the cylinder, this is known as load. The spark tables actual use that not MAP.

From the airmass and a model of volumetric effeciency it can work backwards and estimate the manifold pressure. Used for things like the throttle body and injector flow rates.

From the throttle body model, airflow rate, and manifold pressure, it can work backwards some more and come up with what it thinks the barometric pressure is.

With out the engine running, air isn't flowing, I wouldn't worry to much about what these numbers say.

 

[K4fxd]

So even though my scanner shows atmospheric pressure , which is wrong, tonight it shows 13.2 psi, the PCM ignores it or never sees it?

So how does it figure air density?

Thank you for explaining this.

 

[markmurfie]

What does it need to know air density for? It knows the air density in the cylinder, thats far more important for all things engine control related. It knows the mass of the air flowing in, and it knows the volume of the cylinder. mass/volume= density.

It does/ can figure out air density, by using the MAF sensor to get to barometric and the ambient air temperature sensor. If thats needed for anything.

IF you want to know DA, buy an external meter. The car will just run better on its own because better DA means a better in cylinder air density.

 

[K4fxd]

I kinda figured it out after I asked the question. I've been noticing my MAF being off at certain periods and wondered if this has anything to do with it.

What I mean by off is on some logs it will show LT + ST, cell will be .53 and the cell next to it will be 5.36 and the next cell will be 1.58

On other logs it will not have the so called flier.

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