Does anyone else experience the vac pump running when depressing the brake pedal on this v10? I never even notice it kick on on my other audis but on the v10 it runs often when I take my foot off the brake pedal. Ecu measures my mani vac at around 12-13 inches at idle. I did read some audi ssb at some point that mentioned the lack of vacuum on these engines during cold start and the requirement for the vac pump to cycle to run more than other smaller engines. I just am wondering if anyone is experiencing the same. I do have hard brake pedal and plenty of braking power / modulation…
Anyone else have their vac pump, after starting car, run immediately after pressing brake pedal?
Not that I have noticed. Have you put a VAG-COM on it to see if there are any indications of a problem? I do not know what measuring blocks to look at, but my guess is there is something that would indicate if there is a pressure problem.
Ed
For Reference
http://www.volkspage.net/technik/ssp/ssp/SSP_257.pdf
See, the car only does this during the initial startup “enrichment cycle.” But when motor is warm, the throttle plate is more closed, I do not hear the vac pump running. Just food for thought. Still seems like an abnormality to me. I am going to try and see if vcds shows me anything.
Also this bulletin mentions elevation effects, possibly that has something to do with it
So did a log today available in .xls HERE and it appears that the vacuum pump turns on when the pressure builds over ~450mbar which coincides with the above SSP on page 15 that states the motor will turn on at about 540mbar (half of one atmosphere / ~7psi) with a given ~170 mbar hysteresis factor. So that system is working correctly.
However still does not resolve the issue as to why the brake booster is not getting sufficient vacuum pressure from the engine itself and relying on the vacuum pump to make the system work. VCDS measures the engine having 12inHg vacuum after warmed up at idle. This should be sufficient vacuum to feed the booster.
Last, if you notice from the log, the pressure stays in the booster and there is not a bleed off of vacuum “aka there is not a leak” I am able to press the brake pedal ~2 or 3 times before the brake booster vacuum kicks on.
I am not able to take a similar log in my tt or q7 as they are a newer platform but they certainly do not operate this way.
I am wondering if there is a simple check valve somewhere that is afu causing no vacuum to be fed to the booster from the engine…
And is his normal? When I squeeze the hose coming out of the IM into the “venturi” suction pump it stops hissing. Wondering if this suction pump or hose may be bad? Anyone else feel like trying this on their car and see if they can replicate my findings? The hissing sound is really loud, may be the root of my issues
Appears that if the venturi valve “suction jet pump” fails it will actually supply no vacuum causing the pedal to go hard. So still back to original issue, I am wondering how to get MORE vacuum into the system from the engine. Sort of at a loss here
Just so you’re not talking to yourself 
, I have been following along. Wish I could help, but you’re already light years ahead of my diagnostic abilities.
