tekkie

I have a Cobb tune that was working at 1.2 bar and now it’s maxing at .5, I pressure tested at 20psi from turbo to turbo and found a few leaks and fixed those and now it’s holding fine

i reloaded the tune again but no difference, looked at the maf and it looks brand new, I took the divertor valves apart and verified they are fine, zip tied every connector I could find including the n75, no errors on the ecu, no white smoke

any ideas? I am lost on why this is happening, the car only has 28k miles

jdexter

double check that there are no leaks. Then check your wastegates. You can then log whats happening and look at the n75 duty cycle. If there are no leaks, then one or both wastegates are stuck open... at least thats my bet

Carlo_Carrera

So does the car boost to normal levels, .7 to .8 bar, without the Cobb tune?

TrillyPop

Yea I agree with jdexter - check the wastegates.

tekkie

Thanks guys I will have a look there

tekkie

Unhooked wastegate from n75 and weeeeeee it went up to 1.2 before I let off, so a new n75 ordered and hopefully it’s that

jdexter

so that is a terrible idea. If you unhook the pressure pipe to your wastegate, so that no pressure feeds back to it, the turbo is going to go as fast as it can. One of two things will occur, perhaps both. The turbo will spin itself to death, or the engine will explode. Its very unlikely the n75 died, but who knows. In any case, you should be logging the duty cycle on the n75 and see whats happening there. Also you can make sure the wastegates are working by appying pressure at the actuator.

PCAR996C2

Bad N75 valve is not uncommon. Its was causing my car to over boost but it can also cause it to under boost.

https://rennlist.com/forums/996-turbo-forum/1079888-boost-issues.html

pfbz

pretty simple to bench-test an N75 valve...

TrillyPop

Bad N75 is plausible but not common. Much more likely is that one of the lines connected to it is leaking.

tekkie

N75 was busted, it was either stuck open or closed, put power to it no change, put the new one in and all is good again.

PCAR996C2

Good to hear the N75 valve fixed the problem. Suncoast say this is a common problem, https://www.suncoastparts.com/product/SKUN75.html and they are so cheap I don't know why you wouldn't even try this first.

tekkie

yeah I figured if it was not that I would need one some day so I would have it, as you said it’s cheap

pfbz

I keep a spare N75 in my parts box!

k9turbo

i need to throw that part at my 0234 intermittent code. cant remember ever replacing one.

did you diy it? and if so, is it just two screws or do i need a t20 security etc like needed for the maf?