Low Boost?

Brett Dikeman brett at cloud9.net
Mon May 20 01:22:44 EDT 2002

At 11:49 PM -0400 5/19/02, Dan Simoes wrote:
>I have almost the same behavior.

Including the bucking?

>   I just replaced my wastegate frequency
>valve (WGFV) which got me above 1.3, but I rarely see 1.6 or 1.7,

The Official Audi Test Procedure is starting in 4th gear, 2k RPMs,
nail it and by 3k you should have 1.83 bar give or take a small
amount, measured off a calibrated digital boost gauge, not the dash.

>  and I do get better results by feathering the boost in (as opposed
>to stepping on it)

Several others have noticed this behavior; I mentioned it a couple
years ago, shortly after I got the car, and a couple of people
replied basically to the effect of "yeah, what's up with that?"
Chris Miller reminded us that under a certain percentage of
throttle(1/3rd I believe?), the ECU doesn't open the wastegate...or
something like that.

>  I'm pretty sure the blowoff valve (or whatever it's called) is OK.

I think Audi calls it an "overrun cutoff valve".  Phil and I had a
friendly argument about it a while back :-)

Severe bucking is not normal at all, Chris...it usually means that
there's a loose or split hose; the split opens up at a certain
pressure, letting out metered air, causing the mixture to go rich,
and you loose power...then boost drops, the split closes...mixture
goes back to normal...repeat.  Check the infamous Michellin Man hose,
among other things.  I had this kind of behavior when I accidentally
left a hose clamp loose.

FYI, dead giveaway on the bypass valve is when the car stumbles or
stalls when coming to a stop.

Dan, let the car warm up(drive it for 5-10 minutes) and then using
VAG-COM, write down the live registers(I forget what VAG-COM calls
it..data block 0 or something?), and post back to the list...maybe
someone can make sure they're all within spec.  Personally, I don't
think the Planar O2 sensor you used is compatible, but when I posted
on the main list asking about this, nobody responded.  Still working
on tracking that one down.  Your initial comments were positive, and
low boost can certainly be other things, but I'm very suspicious of
that O2 sensor.

"They that give up essential liberty to obtain temporary
safety deserve neither liberty nor safety." - Ben Franklin

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