i'm boosting really hard....and i think my throttle is cutting

[alosh]

well my car is in the shop right now for a completely unrelated incident, but recently i've been hunting down "a boost leak".

the main problem was high in the rpms of 4th, and anywhere in 5th or 6th, my car would pull hard and then just cut and go into a limp mode. I would be stuck in limp until a few drives later, it would come hard on boost.

because of that, i built a pressure tester adn replaced:

-F hose with a homedepot solid one
-TBB with a strong silicone one
-new 710Ns
-and new sparks for good measure

after all this, and no leaks when doing a pressure test, i still had the same problem... i had been so lazy before, i decided i've always had a boost gauge in my other cars, and the s4 deserves one too. so i made my own in my center vent using a VDO (looks badass btw)...

and i find out my car boosts hard, i mean really hard, for just an APR tune. i had my brother ride in the car and i did multiple runs in every gear.

in 1st: im holding 15psi
in 2nd: im holding 18psi
in 3rd: im holding 20 psi
in 4th: im holding 22 psi
in 5th: im holding 24 psi
in 6th: im holding 25 psi+ because thats the end of my gauge

so i figure the limp mode is not really limp and maybe its throttle cut (but why is my car acting like its in limp after???). i don't know why my car is boosting this high, and i really am not BSing, it pulls EXTREMELY hard on the highway for maybe 2 seconds.

im baffled, please help out, i want my car running well again.

and also, no CELs

TIA

[blmlozz]

It's either a n75 or wastegate issue. Check to make sure the lines running to your wastegates are not torn or leaking.

[AudiSportB5S4]

^^ yeah ^^. looking at your N75 take off the line coming from the driver side fender or right side however you want to call it, and try blowing into that line. It should hold pressure and be impossible to blow any air in there really. Try that, that would test if your wastegate lines are torn or not.

if that yields nothing, I would try getting a new N75 valve, as I had a similar issue with boost going a little crazy and a new N75 cured it right away.

[alosh]

ill do that...you don't think its the tune do you...

i thought apr was "conservative" .

should i have a CEL for the N75

[AudiSportB5S4]

ill do that...you don't think its the tune do you...

i thought apr was "conservative" .

should i have a CEL for the N75

no I wouldn't say it's the tune. I never had a CEL for N75, and that was the case. I found my problem by putting a MBC in standalone in place of the N75, if you can control your boost and it hits and holds where you set it, then you are looking at buying a N75.

[00s4slvr]

yeah n75 almost never will throw a CEL. DONT GET THE RACE ONE!!! i have it and i dont trust it. i ordered the stock one and will be putting that back into my car.

[alosh]

yea i learned from my days with 1.8Ts not to do race N75s.

stock work just fine.

i guess ill post up when i get my car back from the shop for control arms

[spinny]

*shrug* I have a race N75 and it works just fine...

when my N75 goes I'm just going MBC in standalone.


I'd log the car to see the actual boost vs request boost, and then check the N75 duty cycle. You'll know right away if it's a bad N75.

Good luck.

[AudiSportB5S4]

N75 race valves will usually only work well on a car that is tuned for one... that isnt any new information that has been known for years on these forums. stickkk with stock on these cars unless you have a reason to go otherwise!

[00s4slvr]

N75 race valves will usually only work well on a car that is tuned for one... that isnt any new information that has been known for years on these forums. stickkk with stock on these cars unless you have a reason to go otherwise!

well i learned the hard way