General Turbocharger boost pressure sensor.

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General Turbocharger boost pressure sensor.

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Hi to all,

Would anyone have information on the turbo boost pressure sensor.

1. Its actual location.

2. Its prime function.

3. What makes it operate and why.

4. Which components are operated by its involvement.

5. The pressure measurements expected to see if connected via diagnostics tool.

The vehicle is a fiat doblo 1.3 multijet 2005 non dpf model.

I have no issues at the moment, but would like to have some info on this sensor.

Thanks a mill.

John.
 
Air pressure is measured in the manifold or air intake after the turbo by a Manifold Absolute Pressure Sensor (or MAP sensor).

1, On the these I believe it's down the back under the engine cover/airbox, in the top of the manifold.
Seen here in the last few pics
http://www.fiatlinea.org/fiat_linea_bakim/map_sensor_temizligi-t3681.0.html

2, It detects what air pressure is being fed into the engine and along with the Mass Air Flow sensor (MAF sensor) the ECU can work out the available oxygen, then works out the correct fuel strategy.

3, It's a sensor, so it will receive a signal voltage (often 5v), alters it due to whatever is happening and returns this altered voltage back to the ECU.
It works like a balloon with a little air in it, put the balloon in a vacuum and it expands (though the amount of air inside stays the same), put it under pressure and it contracts (again, the amount of air inside stays the same).

4, As already stated, it's signal, along with other sensor readings help the ECU work out fueling stategies, so will influence the injector timings and bandwidths, basically the more oxygen available, the more fuel it can throw in.

As boost pressure is not constant, it will also influence turbo control in some applications with modern Variable Vane Turbos (older VGT's and wastegate turbos tend to control themselves via a vacuum loop), so as manifold pressure rises, the vanes will contract and limit boost.

Engines can only handle a certain amount of boost reliably, so in general the faster the engine/exhaust gases, the higher the boost, the more the vanes/wastegate will contract and vice versa.
If the ECU detects too high a MAP signal, it will protect the engine by tripping limp mode and limit power/boost.

5, Again boost is related to engine/exhaust gas speed but vanes and wastegates try to control boost to a useable level.
Generally they will boost to around 1 bar above atmospheric pressure (which is near enough 1 bar at sea level) but it's often reported by diagnositic tools in kilopascals (kPa's).
 
Hi Goudrons,

Thank you so much for a very informative and comprehensive explanation of the turbo boost

pressure sensor. Understand the various sensors and their operation, makes life alot easier,

Getting to know your car better.

While I have you Goudrons, can I ask you one last thing.

The 1.3 multijet engine, does this engine incorperate some form of a wastegate arrangement?

As you have mentioned, to relieve boost pressure, if it gets too high.

Thanks a million Goudrons, very much appreciated.

John.
 
I think Fiat use a couple of different turbos on this engine, one a variable vane (VGT) and one a wastegate.
I seem to think the higher output engines use the variable and the rest use the wastegate.

The simplest way to operate a wastegate uses nothing but diaphragm, a spring and changing air pressure from the charged air side of the turbo fed in to the diaghragm/spring.
It's often called a closed loop system or pneumatic.

Differing air pressures taken from the charged air side of the turbo operate a diaphragm/spring via a small pipe that's then connected to the wastegate/vane actuating arm.

As rpms rise, the turbo spins fasters, so changes the air pressure on the charged air side, this causes the diaphragm to move, which operates the vanes/wastegates.

There are other ways to operate a wastegate or vanes but they aren't usually used by car makers.
Hydraulic use engine oil pressure.
And electric motors have been used on some chargers.
 
Hi Goudrons,

Thanks for the additional information on the various types of turbos, and how they work.

We were replacing the drivers side driveshaft today, and while I was underneath I had looksie

regarding which type was on this doblo. Turns out its the wategate arrangement model. I

could see the diaphragm housing next to the turbo. With a vacuum pipe in at one end,

and the arm/lever coming out at the opposite end. Tomorrow, I plan putting a vacuum gauge

on the pipe and see if the arm/lever moves freely.

Again, thanks a mill Goudrons.

John.
 
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