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Intake manifold Pressure sensor (MAP),


Some info here Richard:

http://en.wikipedia.org/wiki/MAP_sensor

I believe that the MAP sensor has superceded the MAF [mass air flow] sensor and I doubt that it will be suitable for your 996.

Jeff
 

Here's an explanation of how it works Richard. A bit simplistic but you'll get the idea.

https://www.youtube.com/watch?v=gq4szm5Re0g

It seems to be a bit more rugged and less prone to contamination than the hot wire method used in a MAF sensor but I very much doubt that it could be a 996 retro-fit because of the bespoke DME programming required.

Jeff
 
I thought that MAF and MAP were total different, one measuring flow the other pressure?

And if it replaces it, why do some Cars have both?.
 

Both are used to "measure" air-flow rate Richard, the MAF using a hot wire maintained at a constant temperature in the flow and the MAP using manifold absolute pressure and temperature. In each case, the voltages are fed to the DME which derives the flow rate from the data and adjusts the fuel flow to the injectors accordingly.

I've really no idea why both devices would be used together other than for the DME to compute an average value. Or perhaps each device is more accurate for different air-flow rates and the DME switches from one to the other accordingly throughout the engine speed range.

Jeff

 

ORIGINAL: Motorhead


Both are used to "measure" air-flow rate Richard, the MAF using a hot wire maintained at a constant temperature in the flow and the MAP using manifold absolute pressure and temperature. In each case, the voltages are fed to the DME which derives the flow rate from the data and adjusts the fuel flow to the injectors accordingly.

I've really no idea why both devices would be used together other than for the DME to compute an average value. Or perhaps each device is more accurate for different air-flow rates and the DME switches from one to the other accordingly throughout the engine speed range.

Jeff
Click to expand...

Quite, why some cars use both is beyond me?.
 
Thanks for that Jeff,

just some more info I Googled

Each EFI car today is equipped with either a MAF sensor ( mass air flow) or a MAP sensor ( mass air pressure). Some cars are even equipped with both a MAF and a MAP sensor"¦..example a Mitsubishi Evo X. So what do these sensors do and what is the difference?


A map sensor is a sensor that is installed somewhere in the intake manifold or very close to it. It is a sensor that detects the pressure found in the manifold. On a naturally aspirated motor this sensor will be detecting the negative pressure found in the intake manifold which we call vacuum. If the car is equipped with Forced Induction, then this sensor will be in charge of not only detecting the vacuum but the actual positive pressure in the manifold as well.

Because this sensor must cover both vacuum and pressure they come in different size measuring ranges. These ranges are often given in the unit of Bar instead of PSI. Bar is the metric unit for pressure while PSI is the standard unit. When choosing a MAP sensor choose a sensor that will be appropriate for the amount of vacuum and pressure your particular motor will see.
MAF Sensor

MAF SensorMAF SENSORMAF SENSOR

While there are many kinds of maf sensors let's focus more on what they are. A maf sensor is a device that measures the mass air flow, hence its name. It measures the CFM or mass of air that passes by the sensor and outputs the actual flow of air to the ECU. What can be confusing when dealing with and tuning a maf sensor is that the computer will often interpret the MAF data to depict an actual load value instead of an actual number in CFM of flow. Because of this, MAF sensors can be harder to tune based on the interpretation of the ECU for a given air flow.
MAP sensor VS. MAF sensor

While both sensors accomplish the same thing we could give the +'s of each.

MAP sensor

1. Even if an intake pipe blows off or there is a vacuum hose leak the car will run the same, as the actual manifold pressure will not be any different so you will not be left stranded some where.

2. Sensor reads actual load so there is no guessing what load level the engine is seeing.

MAF sensor

1. The amount of CFM entering the motor is VERY accurate even at low air flow levels. Because of this MAF sensors have a tendency to get better MPG's (miles per gallon).

2. Most have a built in AIT( Air Intake Temperature ) sensor so you can monitor your actual air intake temps at the sensor.

taken from http://www.enginebasics.com/EFI%20Tuning/MAP%20vs%20MAF.html

I'm still confused[&:]
But know as to why you would only use one not both
 

Yes, I'd come across the same article Richard. Some of the internet chat appears to come from the turbo-tuning fraternity where perhaps the MAP has some advantage in that it measures the actual intake manifold depression, or pressure in the case of a turbo engine, the latter being a very useful parameter for turbo regulation.

To me, the pressure sensor of the MAP seems to be a more rugged construction than that of the exposed hot wire of the MAF; you only have to read various forum postings to learn about engine problems caused by MAF sensor contamination.

Like you, I'm still puzzled as to why an engine would need both sensors but can only guess that one is used to moderate the other in the turbocharged Mitsubishi Evo X installation.

Jeff
 
Just FYI Jeff, the Porsche 9x6 and 9x7 MAFs are hot film, rather than hot wire. Same principle, but less prone to contamination, I believe.
 

ORIGINAL: Richard Hamilton

Just FYI Jeff, the Porsche 9x6 and 9x7 MAFs are hot film, rather than hot wire. Same principle, but less prone to contamination, I believe.
Click to expand...

Thanks Richard. Googling the subject certainly brings up a lot of information on different types of mass flow sensors [e.g. http://en.wikipedia.org/wiki/Mass_flow_sensor].

Just out of interest, do you know if Porsche now use MAP sensors on the latest cars?

Jeff
 
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