No Boost,No CEL

[JuStJPpLaY]

Ive read everything on forums,checked for leaks,checked turbo westgates with vacuum and removed downpipes to check gates,checked Boost pressure sensor,bypass 710n just for the test,EGT shows 0 for both sides for some reason(prob chip).Ive tested the car with vag com/odis,kts,launch.Did reset learnings for throttle etc. Cleared throttle and injectors in ultrasound and tested them if they work.Fueling is good 4bar up to 7k rpm.New sparks with coils and fuel pressure regulator.Good compression.I bought the car with the problem and can't fig it out.When it wants 600mbar it gives around 300.On 6th gear full thrtl max 160-170 km/h.No boost leaks (tested with smoke)and no boost maybe ECM cuts fueling but for what reason.What to look for .....?

[TwoSnelz]

Have tuner check WG Duty cycle?

Sent from my SM-G973U using Audizine Forum mobile app

[CELison]

Both turbos spin freely and you're sure the TB is opening correctly? I had a dead TB that created a zero boost condition.

[JuStJPpLaY]

I disconnected the gates for the test so i can see does they overboost but it jumps from 300mbar to 400 or so

[JuStJPpLaY]

Both turbos spin freely and you're sure the TB is opening correctly? I had a dead TB that created a zero boost condition.

No dtc for that and when i press accelerator it gives a sounds so its moving

[CELison]

No dtc for that and when i press accelerator it gives a sounds so its moving

Um, ok then.

[JuStJPpLaY]

I tried without exhaust just on downpipes if something is stopping gasses go tru but nothing

[evalegacy]

I'm assuming you have a boost gauge. What is it at idle? should be between 15Hg and 20Hg (around -18psi) if holding vacuum properly. While driving and you punch the throttle, if the gauge jumps to zero and instantly stops then it seems likely it's an electronic controlled issue (EGT or N75). Unplug your N75 and it should boost to wastegate pressure (around 5-7psi on stock and k04 turbos); carefully watch as not to overboost if there's a wastegate issue.

I am curious about your EGT sensors though reading zero. When they're bad, it can cause ECU to limit boost so the engine doesn't lean out too much and cause catastrophic failure. These are commonly known to go out on high mileage S4's. When I bought my S4 from a previous owner, both EGT sensors were bad and it would not boost. I left the EGT sensors screwed in but disconnected them from the plugs and connected diodes from eBay to tell ECU to ignore them.

[CELison]

N75 isn't able to create zero boost if all hardware is fine. The least it can do is WG pressure.

[JuStJPpLaY]

I'm assuming you have a boost gauge. What is it at idle? should be between 15Hg and 20Hg (around -18psi) if holding vacuum properly. While driving and you punch the throttle, if the gauge jumps to zero and instantly stops then it seems likely it's an electronic controlled issue (EGT or N75). Unplug your N75 and it should boost to wastegate pressure (around 5-7psi on stock and k04 turbos); carefully watch as not to overboost if there's a wastegate issue.

I am curious about your EGT sensors though reading zero. When they're bad, it can cause ECU to limit boost so the engine doesn't lean out too much and cause catastrophic failure. These are commonly known to go out on high mileage S4's. When I bought my S4 from a previous owner, both EGT sensors were bad and it would not boost. I left the EGT sensors screwed in but disconnected them from the plugs and connected diodes from eBay to tell ECU to ignore them.

Im watching it with diagnostics about the boost.The vacuum at idle is 0.6 bar thats around 8-9psi, but didn't check when i punch throttle so i will buy one tomorrow and check.When i bought the car i connected it do diag and it has EGT bank 1 fault.I though thats the reason the car is not running properly.When i get it ,i opened the sensor and i solder the pins, then the fault was gone but the car continues not to boost.I tried without MAF (rs4 installed)and with original maf for s4 and nothing,without o2 sensors nothing,without n75 same,car is running rs4 injectors too.Its 225k km and its preserved.I will check for those diodes

[JuStJPpLaY]

Someone changed the original n75 to this from tt i guess.I returned back the original valve and properly installed pipes like original s4