im not very knowledgeable about engine work and i know some of you are absolute genious'.

anyway... sometimes when i hit the gas, the turbo's kick in, and then as it pulls the turbo kinda cuts out.. like its missing or something... what is this?? air leak? boost leak? its on a 2001 Audi S4. i don't like the set up of audi forums and i love this sight and i wish i got a Z.. anyway, if anyway could tell me what this feeling is I'D GREATLY APPRECIATE IT!

its not turbo lag, has no problem spooling up, just when it really starts to generate power, it kinda cuts out.. 107,000 miles on stock turbos.

 

Sounds like it may be overboosting to me.

 

Overboosting? If that was the case the turbo wouldn't cut out but one of his rods would. Either its getting so lean up top the ECU is cutting timing or your bearings are shot on your turbocharger. The latter is less likely..

 

fuel injectors ? 107,000 miles.. they might be filthy.. pump? fuel filter filthy? I guess it could be anything with 107,000 miles

 

It could be a bunch of things and you can spend a lot of time guessing. You need to have someone knowledgeable on turbo's troubleshoot it. A boost gauge, fuel pressure gauge and wideband sensor are necessities to point you in the right direction.

 

Pressure test it. Its most likly a vacumme leak. A common problem with B5 S4's are there throttle body boot it tears very easily so that would definetly need to be replced seeing how it has over 100 thousand miles.