can a boost gauge go bad????
 

I have a autometer boost gauge that was in the car when i got it. I have a 10 psi pulley on my supercharger, but it only saw 8 psi. Recently the gauge seems to be gettin more and more innacurate....today it wouldnt get over 4 psi, but the cars performance hasnt changed. I think the gauge has gone bad, but is that even possible?
Isnt there some way that you can use the pressure reading on a vafc as a boost gauge....like when it goes into the + side? does anyone know the conversion?

Re:can a boost gauge go bad????
 

I had a friend with the smaller pully and hte SC topped out at 8 PSI. I got it to go to 11 by going to the AFC hack and ditching all that relay ---- that came with the kit. It runs 11 PSI all day long.

Re:can a boost gauge go bad????
 

I just got done with the hack....before the hack i was gettin 8 to 9 psi....now i am only gettin 7 but the car feels just as strong :-\

Re:can a boost gauge go bad????
 

vaccume leak?

Re:can a boost gauge go bad????
 

yep...check the vacuum line that runs to your boost gauge sometime a little leak will throw it off on the gauge. I use to own a autometer boost gauge it happen to me and a few months it went out. So i just purchase a new one.

Re:can a boost gauge go bad????
 

if the guage is old,tap it a few times while you're in boost, my buddy has had his autometer on his C32 (supercharged) for about a year now, and when in full boost (don't gimme ---- for the "full" boost thing, his SC is a wierd clutch driven type of deal that isn't always in boost) it'll say 16psi, then he'll tap it a few times and it'll "unstick" itself and read 18-19psi

Re:can a boost gauge go bad????
 

How do you read boost using the vafc....does anyone know?

Re:can a boost gauge go bad????
 

I thought we had already discussed this...

Use your bar reading from your MAP sensor, and multiply that by 14.5...

So if you're reading .5 bar on your V/S-AFC.. you're reading ~7.25 psi..

PSI = Bar * 14.5

Re:can a boost gauge go bad????
 

How do you do that exactly? run a line from your map sensor?

Re:can a boost gauge go bad????
 

how do i know if that is hooked up correctly....the highest i have gotten is .45....but i have a 10 lb pulley on my supercharger so somethin is wrong. could a vaccum leak elsewhere cause this?
there are 3 pressure settings in the setup on the vafc, which one do i need to have it set on?

Re:can a boost gauge go bad????
 

the different pressure settings are just what units you want the MAP to be displayed as. use bar, it's easily convertable to PSI with the above formula

Re:can a boost gauge go bad????
 

but when it goes to the positive side, it says cchg or something like that....is that the same as bar?

Re:can a boost gauge go bad????
 

No... change your settings. :P

Someone really has your V-AFC all wacked out.

Re:can a boost gauge go bad????
 

What should i change it to?

Re:can a boost gauge go bad????
 

I'm looking over the manual and it doesn't look like you can. Weird, I always thought it was in Bar, never really paid attention I guess, dumb on my part.

Anyway, though, try this:

Multiply by 0.98067 which yeilds Bar, then multiply that by 14.5 which yeilds psi.

So your formula is: psi = (x * 98067) * 14.5

Still doens't seem to help you, but does ring accurate for my old V-AFC setup. On a stock internally wastegated 14b (TD05H), I would get .562 on my V-AFC pressure gauge. Run this through the formula and you get, 7.99 psi! Almost dead on for 8psi, which is what the internal wastegate is set for...

I'm still not sure why you're not coming out which more psi. Maybe there is a hardware problem.

Re:can a boost gauge go bad????
 

mine reads in bar, there are three different sttings, CM mercury (CCHG), Bar, and something else i can't remember. why they didn't put PSI in there I could never tell you. go into the settings menu and change the pressure setting to bar.

Re:can a boost gauge go bad????
 

hate to say it, but i'm pretty sure atmospheric pressure is 14.7 psi. might as well use the right figure if you're going to mutiply by .98067... and no, i'm not thinking of stoichiometric air/fuel ratio, despite it being the same number.

Re:can a boost gauge go bad????
 

what is the setting for bar?

Re:can a boost gauge go bad????
 

-760mmHg ~ 0mmHg

-770mmHg ~ +1.0kg/cm^2

-770mmHg ~ +2.0kg/cm^2

Those are the 3 options, which do i need?

Re:can a boost gauge go bad????
 

-770mmHg ~ +1.0kg/cm^2

Re:can a boost gauge go bad????
 

14.7 is atmosphereic pressure, but that's not the conversion factor.. If I wanted to get "technical", the formula would be..

psi = (x * 98067) * 14.5037738

...but thanks anyway.

Re:can a boost gauge go bad????
 

i guess i was thinking atmospheres and bars were the same thing ???

Re:can a boost gauge go bad????
 

Nah. It's because atmospheric pressure is in constant flux ... changes based upon your location, weather, altitutde, etc.

Re:can a boost gauge go bad????
 

well i figured out my problem....the belt tensioner was loose and the belt was slippin at high rpm's....now im gettin .53 bar and my boost gauge is readin over 8 psi again.....question is will the vafc hack affect the bar reading on the vafc?
is the boost gauge more accurate than the vafc?

Re:can a boost gauge go bad????
 

No, the V-AFC calculates boost based off of your MAP sensor. This is done on the untouched signal, so it's reading straight and accurate.

A boost gauge could have potential leaks at high pressures in the line, and could also just be "off". I know on my Autometer Ultra-Lite, my need at ambient sits about .5 psi above 0.

Now, if we think about this, this is incorrect as I am not "below" sea level. If anything, it should read a bit less if calibrated at 14.7 absolute pressure.

Re:can a boost gauge go bad????
 

hmmmm....so i might have more that .53 bar depending on where im at related to sea level?

Re:can a boost gauge go bad????
 

IT wouldn't change enough for you to notice with tuning only with an AFC.

..you would see it with a wideband though, due to the desity ratio.

Re:can a boost gauge go bad????
 

i have a wideband on the way....wohoo