In general when does the turbo spool up and/or boost in city and also in freeway driving?

My TII is new to me so I’m not sure if the turbo is working normally. When I first got it, the turbo barely spooled up even to 0 then after some mechanic work on its injectors and other components it did spool up and boost but only to about 3 psi only at higher freeway speeds in 4th gear. The wastegate was not stuck and the turbo was not stuck.

In city driving going uphill under load and in 3rd gear it does spool and boost but only about 3psi.

Should the turbo spool up to 0 more often even in street driving?

does the car have to be under load regardless of speed for it to spool up and boost? In a lower gear such as 2nd and 3rd in street and 3rd and 4th on the freeway?

 

I have a GXL but I recently swapped an S5 turbo motor into it. I'm not sure if you have an S5 or an S4 turbo but from my experinence when your at WoT you should be at 0 vacuum pretty much instantly as the throttle plate is no longer restricting airflow. If its not doing that there may be an issue with your throttle so if that sounds like your issue I would take off your intake up to the TB, have somebody or something stamp on the gas and see how wide the throttle body opens. As far as the turbo, when I got mine (which had some miles on it) it would spool to about 5-7lbs of boost. These cars are not getting any younger, and if the wastegate spring is old it could be weak causing the wastegate to open prematurely.

One more thing about the TB, if you have a stock throttle I would absolutely check for proper opperation because they are way more complicated then they need to be, theres like 5 butterfly valves in there and if any of them arent opening you'll have issues.

 

stock boost on the S4 should be around 5.5psi, you should be seeing positive boost after at least 2500RPMs. sounds like you have some intake leaks to sort through.

with my FC i had a similar issue when i first got it going, it turned out the precat was broken up internally and blocking 80% of the exhaust flow and choking the engine, so that is something to consider too.

grab yourself a $15 endoscope from amazon and peek it in the O2 sensor port to inspect your cat for damage. it should look like a nice flat honeycomb pattern, if it looks like a gravel dump then it needs to be rooted out.