Best place for boost/vacumn sensing ???

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youngsyp

Active Member
Chaps,

Have got an Apexi AVC-R connected up as Apexi suggest but, I'm not convinced that I am taking the vacumn/boost pressure reading from the most ideal place. Could anyone shed any light on where the best place would be to have the pressure sensor piped into, to get the most accurate and consistent reading ?

Cheers

Paul
 
G

goob

Guest
i T'd into this vaccum pipe for a reading. pipe comes out just underneath the small black box with arrow pointing to it.

hope it helps

 
Y

youngsyp

Active Member
That's where the OE boost guage measures from and where I have plumbed in my Autometer boost guage.

That's still along way from the plenum though, I was thinking of somewhere a bit closer ?!
 
Y

youngsyp

Active Member
oldaneal said:
think i u follow the pipe back it t's off and goes up to the fuel presure regulator could t it off from there
Click to expand...
That's where it's T'd off now, where Apexi recommend to take the reading from :!:

I'll explain my reservations as that might help. Basically, the pressure sensor is currently T'd into the same pipe as the FPR, as Apexi recommend. However, I have been having boost spikes and so investigated a bit. The AVC-R is currently set to 1.00 kg/cm but, spikes as high as 1.20 kg/cm. It appears that the boost pressure spikes, when I lift off the gas to change gear which, strikes me as a bit strange as the turbo will no longer be loaded up then, and so should not be making boost ?! This leads me to believe that the source where the pressure sensor is taking it's reading, is not very accurate. And this is why I want a vacumn take off that is more accurate and reliable than the current one, preferably as close to the plenum as possible and with nothing else T'd into it !

Cheers

Paul
 
A

AJ4

Guest
Boost pressure always spikes when you lift off the gas. Instead of all the air going into the cylinders, the momentum of the air 'piles up' against the closed throttle bodies and you will see a spike in boost. Only happens for an instant, and the pressure increase is in the plenum side, not the engine side so its normal and nothing to worry about.
 
Y

youngsyp

Active Member
AJ4 said:
Boost pressure always spikes when you lift off the gas. Instead of all the air going into the cylinders, the momentum of the air 'piles up' against the closed throttle bodies and you will see a spike in boost. Only happens for an instant, and the pressure increase is in the plenum side, not the engine side so its normal and nothing to worry about.
Click to expand...
That makes total sense. I don't even see it spike, I just have peak hold on and that records it. Guess I need to stop worrying about it then :D

Just out of curiosity, does this boost spike, cause the ecu to pump in fuel, once the throttle is closed too then ? I mean, the ecu must sense the sudden hike in positive pressure and try to compensate with more fuel ?! I guess the TPS tells the ecu that the throttle is closed and not to bother, though ?!

Is there a vacumn 'take off' that I can measure the boost/vacumn 'engine side' anywhere ?
 
A

AJ4

Guest
The fuel is metered by the amount of airflow through the AFM, not on pressure, so the ecu will already have metered that air and supplied the right fuel. Also, when the throttle position sensor falls below a certain amount, the ecu is triggered into 'idle' mode, not the main map.

There is a 'listening' post on each throttle body that you attach a vacuum guage to, to balance the throttles, I think its after the throttle plate ( can't remember :oops: ). They normally have little black rubber johnnies on them to stop air leaking in.
 
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