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wont boost past 9psi!

14K views 15 replies 2 participants last post by  titter 
#1 ·
i dont know what to do next for my 02 wrx. ive checked everything for leaks, everythings in the right spot. when i disconnect the bcs wire harness i get 5psi and when i disconnect the vacuum line to the wastegate i get 20psi spikes. when everything is hooked up i cant get past 9psi. ive had the car a little over 2 weeks now with no avail to tapping into its full boost potential. 9lbs feels nice but i really want that 18psi. i have catless up and down pipes, EL headers, TBE, fmic, sti pink injectors, short ram intake. running a modified version of testes1010 stg 2 tune.
 
#2 ·
did you bypass the bcs and get 5psi? as in were you just running wastegate pressure and got 5psi? because the td04 wastegate is set to 7psi. if your not reaching 7psi solely on wastegate pressure there is a problem with your wastegate. its not building boost properly. perhaps its not seating correctly? the arm could be nice and stiff but still possibly not seat properly. or there could be a crack in the wastegate or in the hotside housing where the wastegate seals.
 
#4 ·
i dunno. how tight is it already? if theres room to play sure, but i wouldnt overtighten anything just to try to get it to 7psi.

heres something on lowering your TD04 to 5psi... maybe do what he does in reverse?
5psi Wastegate for TD04 - Subaru Impreza GC8 & RS Forum & Community: RS25.com

also that thread says wastegate pressure is 10psi, which seems high. nasioc rates it 7-8psi max from wastegate pressure.

either way, if your only seeing 5psi on wastegate pressure, thats your problem.
 
#6 ·
i re-read the link fully, the guy swapped the actuator from an 80's subaru turbo. so i guess nvm that lol my bad.

still tho, 5psi on wastegate pressure is not good.
 
#8 ·
well my only thought still is something is leaking between your exhaust ports and your wastegate. might be manifold, uppipe, hotside turbo housing... anywhere pressure builds. maybe the actual actuator?

sorry i cant be of much more help than that.

good luck
 
#11 ·
so with the wastegate disconnected you should infinitely build boost till it explodes (sorta)

you know how a wastegate works of course, but i'll explain for the thread to help explain my theory.

as pressure builds the wastegate functions to relieve the pressure that builds up and regulates it according to whatever management you have (ebcs/mbcs). with it disconnected is should stay closed and you should build boost till your turbo is destroyed (could happen instantly, could happen over time). so the jumpy/spikeyness is telling me as its building boost its spitting out leaks. i could be completely wrong, but thats just my therory.

when you had your up-pipe welded, did u re-use the gasket? they are notorious for leaking if re-used. should always use new gaskets.


other than all this, maybe you should consider a turbo upgrade? nothing fancy. find a decent VF series to bolt in to place. with all your mods you have, really, that TD04 is a little small. used VF's can be had fairly cheap (my buddy grabbed a VF30 for $300CAD recently) would easily fix your problem and put you at a power level you would really enjoy.
 
#12 ·
the thing with getting a new turbo is i dont know if i want to keep this 02 or sell it to upgrade to an 06-07. i dont want to put a new turbo on just to turn around and sell it. i do believe a new turbo would relieve me of this whole problem though. your theory doesnt sound too bad, im going to try to check for leaks with brake cleaner. and when i said i got the uppipe welded i meant the manifold. the crack was right where all 4 pipes meet for the uppipe. none of the pipes were taken off.

whats a good way to test the up pipe and down pipe gasket seals?

another thing that seems weird to me is the numbers i put down during logs. i only make ~1.80 engine load and ~120 mass air flow. when i look at numbers from other peoples stage 2 wrxs these two numbers are so much higher. are mine low just because my boost is low?
 
#13 ·
pretty sure you'd hear a pre-turbo exhaust leak if your under your car with the engine running, though i do not reccomend doing so unless you have a lift or inspection pit. otherwise you'll have to take them off and smoke test them or pressure test. and im not the greatest with logging data but what u say makes sense.

i hate to say it, but you might have to take off your turbo and give it a full inspection if u ever want to be 100% sure.


maybe you'll really like it with a new turbo and never want to sell it? lol :)
 
#15 ·
question: so im still getting a misfire on cyl 1 code. If the ecu was pulling boost because of misfire, would that reflect in a log by the ecu lowering the wastegate cycle? or would it pull boost a different way? because today in 4th gear i realized right when i get to ~10psi my engine will sputter and stop building boost. however WGDC remains at 100%. also it wont rev past 5k. maybe im in limp mode? also i cant rev past 5k. how possible is it that all of this is because im in limp mode??
 
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