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      04-21-2017, 06:20 PM   #1
KawBoy
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Vacuum source/MAP location

Hello Everyone,

MAP (#13) is installed on the idle strip (#11), which is the best location as it is right after/below the throttle blades. However, idle strip (#11) is connected to hose (#9) which in turn is connected to the idle control device (#1). I have no idea what this idle control device does, but since the idle strip is not sealed (it is connected to this idle thing through a hose), what kind of reading is the MAP getting?
Motor at idle, vacuum at max; is the idle strip "venting/leaking" some of that vacuum to the idle device?
Forced induction motor at 10psi; is the idle strip "venting/leaking" some pressure to the idle device?

Thank you.

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      04-21-2017, 10:45 PM   #2
Pig Farmer
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Interesting question. The ICV is only open (in pulses) when the throttle plates are closed at idle. The air pulled into the engine when the ICV is open comes from the hose on the fire wall side of the valve. On a stock car, that hose plugs into the bottom of the plenum (so the air has already passed through the air filter). If a supercharger is plumbed the same way, I would guess that the pressure would be the same on both sides of the ICV when the throttle bodies take over and the ICV is closed. In other words, the ICV would not have a reason the leak or release boost. If anything, I would be more concerned with the hose connection with the plenum.
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      04-21-2017, 11:34 PM   #3
KawBoy
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Thank you for your reply.

It seems to me then, if one replace the stock MAP by a MAP from the turbo motors (F80 for instance), one not only will have a very accurate vacuum reading but a very accurate boost reading as well.

The idea is to do the above. It looks to me that the OEM MAPs (TMAPs I believe) are of same physical dimensions, therefore it should be OK to replace them.

Provided all is correct, the only other question is to find out what each one of the four (T)MAP pins do.

Thanks again.
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      04-22-2017, 01:04 PM   #4
Pig Farmer
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So I have some information that may help... P3Cars makes a boost gauge for both the N55 and N54 engines. On the N55, you could get a boost reading by simply plugging into the OBD2 port, but I'm 99% sure it would not provide a vacuum reading. For this reason, I'm not sure if the MAP sensor reads vacuum on the turbo cars, which would seem strange. The P3Cars gauge for the N54 comes with a boost sensor that taps into the vacuum line that controls the diverter/blow off valves. This sensor reads vacuum and boost. If i recall, the N54 was in a -22.1 psi vacuum at idle, and the sensor read boost as high as 19.6 psi on my tuned 135i (and probably capable of much higher readings). The gauge could be set to PSI or Bar, in whole numbers or in tenths. Tapping the diverter valve vacuum line would most likely be the simplest route to install a boost gauge.
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      04-23-2017, 05:45 PM   #5
KawBoy
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Farmer,

I don't know if the OBD2 port shows vacuum, but I think the OEM MAP for the N54/55 and the other tubo motors should read vacuum as well.

Is the diverter valve vacuum line the #5 below?

Thank you for all the great information and help.

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