i have a s5 tII engine and randomly the turbo will not build past 5 or 6psi of boost and at other times it will build right up to 12psi anyone have any ideas on where i should start ?

 

wastegate.

 

checked the wastegate and it is working properly does anyone know how to check the turbo selenoid ?

 

Apply 12 volts and the solenoid should click. Also check ohm reading 30/40. You can also check to see if voltage is going to the solenoid by tapping into the wire at the ecu and checking when under boost.
Usually if the wastegate rod clip is gone, you'll see a boost about 5 lbs all the time, not up to 12, same as the solenoid, normally it either works or doesn't.

 

are you sure the wastegate is working properly. sometimes they can randomly stick. twin scroll actuator. have you checked that?

 

ok so i checked voltage at the selenoid connector under 2700 rpm im gettin 12v over 2700 rpm im gettin 2v also applied power to selenoid and it clicked like supposed to. the way i checked the waste gate was took off the vacuum line to waste gate applied 12psi on the line and watched the wastegate rod move out i right after i tested that drove the car and still only boostin to 5psi. i will have to get back to u on the switching actuator

 

how u test the twin scroll actuator? is it the same thing as the switching actuator ?

 

Are you sure the rod is attached to the flapper? That test by adding air pressure only assures you that the dashpot is working as it should, the rod moves, but if the rod isn't attched you'll only see 5 lbs. max.

 

yes the rod is attached to the flapper i also forgot to mention its a j-spec engine dont know if that will matter ?

 

Leak in the air intake system?

 

do you run a ebc ?

my profec randomly quits from time to time and it will give me 5-6 psi

 

no leaks in the intake and no i dont have an aftermarket electronic boost controller just stock

 

if the ecu is going into limp mode will this problem occur

 

^^
You'd know it if your ECU were in limp mode. The car would be hardly drivable.

 

there is an amazing amount of wrong info in this thread.

S5s don't have twin scroll, and if he's getting 5 psi of boost his wastegate is working fine.

5psi is the size of the stock wastegate, so that points to the factory boost controller valve is the culprit. I forget what it's actually called, but it's mounted to the oil filler neck. have you checked that?

the 12 psi is most likely due to boost creep, which is when your wastegate can't bypass enough air around the turbo exhaust wheel, it should happen at high rpms and higher gears.

check to make sure your stock boost contoller thing is working, and give us some more info. has it always done this?

 

yes i have checked the boost selenoid and it tested fine and no the car hasnt always done this started prolly bout 4000 miles after putting in the jspec turbo engine. what psi do the turbos build from factory is it 12psi ?
if the grounds on the ecu harness arent good enough could this happen randomly ?

 

8.25 PSI as per the Technical Data section in the 89-91 FSM.

 

so does that mean there is a problem there cuz normally im peakin at 12 r 13 n the only performance upgrades i have are redom racing ecu, exhaust (all cats removed) and intake. i am also getting this boost reading from an aftermarket boost gauge

 

dude... you're only making things worse.

the stock wastegate has a 5.5 psi spring, and the boost solonoid raises that pressure to about 7.5 psi just like a boost controller would.

from the factory the turbo can make ridiculous pressure, but it's not efficient above about 12 psi. before I ported my wastegate I use to see 20+ psi on the highway if I accidentally wasn't paying attention, I just controlled the boost with the gas pedal.

it's called boost creep, and as I mentioned before, the stock wastegate isn't big enough to bypass enough exhaust around the turbine. I would actually leave the boost solenoid off until you get your wastegate ported in order to not cause damage to your engine from high boost pressures.

 

How? He mentioned that occasionally he sees 12 PSI and later asked what pressure the S5 turbos built from the factory. I took this comment to mean what the factory boost pressure is from an S5 turbo and wanted to let him know that it is not 12 PSI.

I agree that many people run higher pressures than "factory boost" on a factory turbo, I just didn't want him to get the false impression that his turbo was putting out "normal" pressures at 12 PSI.

 

doesnt the computer tell the wastegate and boost selenoid what to do, when to do it and how much to do ? why im asking is i have a redom racing ecu and was wonderin if it could be programmed to make the turbo peak at 12psi ? and isnt there more than 1 limp mode the ecu can go into depending on what fault the ecu sees ?

 

My factory boost controller didn't work for crap and I removed it and bought an EBC. I even tested it and it clicked.

No the computer does not control the wastegate, it's controlled by vacuum.

 

I hope this video might help you: http://www.tuneyfish.com/video_player.php?vid=235

Its a great demonstration video how to properly set the preload on the wastegate.