^^ Don't worry about the topic title - i'm just trying to make my threads search friendly. But anyway, as my signature says, I'm using a VAFCII controller - when looking at the "pressure" reading --- is it telling you the pressure of the Intake(before/after) the TB or is it the pressure in the intake Manifold????

I went to the apexi site - they used to have the manual online - maybe I just couldn't find it this time. So, this is the last resort - anyway, the reason why I ask is because I have a negative reading of pressure. ....when about 50% throttle - the pressure goes UP!!! to -1.2psi....I'm damn sure thats a problem. I've been having some problems with bogging out and what not. Before 50% throttle, in PSI - it gets down to around -12 or so...maybe less.

I'm thinking it may be the MAP sensor thats giving these readings - I know for a fact that I'm running rich.

The MAP sensor reads opposite of the MAF sensor right? MAF = before TB and MAP = after TB...??? Need some info.

When I say opposite - i mean closed/open throttle.......
Meaning the MAP doesn't read pressure until the throttle is partial open right?

If there's a pressure with a Negative reading - wouldn't that mean its a vacuum??? in Hg(mercury). This is weird. <----

 

??? can I get a bump ???

 

If the units on your VAFC are being displayed in PSI, the value will always be negative (unless you are running FI).

 

NA motors suck air in...

 

-mm/hg = Vaccuum. which is what your pressure is. negative because its being sucked in..

 

Oh - so its measuring the Intake pressure - oh...I thought it was measuring the manifold pressure. So....si -500 mm Hg okay?....

 

don't worry, my VAFC II also goes up to like -1 psi when i hit the throttle. it is normal on every car i've seen with one installed.

 

ya man, mine is at about that. at WOT im at about -12 mm.HG, so its normal

 

for those who have boosted car with vafc. whats the kpa or psi reading when ur on WOT? my boost gauge reads 6psi but when i look at the vafc its -10 kpa. the vafc doesnt read boost but the autometer boost gauge reads boost.

 

THat is because you have a check valve don't you...

Engines unless under open throttle will be in vacuum. Think about it, it is trying to suck air in with the piston and you are restricting that flow with your throttle plate.