96 sti boost problems

[rowingryan]

Hi guys. Ive had a problem with my boost for awile now & its realy starting to piss me off. It will start to boost properly & then at about 4500rpm it sounds as if its pushing alot of air or exaust out somewere & feels realy flat (not getting pushed into the seat). Ive now wired the wastegate shut & im still getting the same problem in 1st & 2nd but 3rd,4th & 5th i can hit boostcut no problem. Ive checked for exaust leaks & the turbos mint. Its also not throwing any codes eitha the throttle position sensor isnt the best & its using alot of fuel & backfiring alot

Any help would be great.

Some specs are

vf23 turbo

greddy type rs bov

rebuilt motor 10k ago

3" from turbo back with a Siamese wastegate pipe.

Trust/Greddy boost tap

[forcefed]

Sounds like a boost leak, check all your intake pipes and intercooler

[rowingryan]

Thats what i thought but why would it hold boost in 3rd,4th & 5th? ill have a good look over it at work or on the weekend & c how it goes. Thanks

[kamineko]

forcefed, yep. check all the intercooler hose clamps, look for oil patterns where a leak might be

also, the flexy-joint in the turbo up-pipe is a common failure. it will sound louder under the bonnet and smell of fumes. not easy to diag tho, as the heat shields cover it

[forcefed]

 rowingryan said:

Thats what i thought but why would it hold boost in 3rd,4th & 5th? ill have a good look over it at work or on the weekend & c how it goes. Thanks

Its more than likly not holding boost in high gears, just the turbo is working hard enuf to make it boost cut,,realy not good for your turbo making it work like this

[rowingryan]

Aaah good point. 1st & 2nd in my car are realy short (3.900) diffs so the turbo probly doesnt have the time to spool that high.

[rowingryan]

Hey guys just goin over some things on the car. if the knock sensor is falty would that retard the timing etc enough to cause the problems im having?

[kamineko]

oh it could be in 'limp' mode, in which case it will just run wastegate boost.

limp mode can be triggered by overboosting, or as you say a dead knock sensor. (or other sensor like TPS)

pull the cel codes, if its in limp mode, there will be a reason thats logged.

after pulling the code, follow the reset procedure. if its happy it should come right, otherwise it will still complain and spit out a code.

if it comes right then after boosting you hit limp again, then its probably overboosting. (i bet you have a 3" downpipe and free exhaust)

see how you get on

[rowingryan]

Doesnt throw any codes apart frm the tps every now & then. Its not the best but it was like that well before the problem started. Ive tested the maifold for leaks & its only leaking air out of the icv to the small air box b4 the turbo. Havnt tested the intercooler or turbo to ic pipe yet & the bov seems to be fine.

Yup 3" all the way with 2 hotdogs & a cannon. Dont wana change it eitha coz its got a more race car sound than droney.

Ill do some more testing tomorrow & get back to u.

[WRXONP]

my old v2 would overboost and hit cut with a 3 inch exhaust but it never threw codes or went into limp because of overboost?

however mine would only boost wastegate pressure with the connectors under the dash pluged in?

[rowingryan]

thts weird. Mine was running 14psi & went rather well 12.55 1/4 mile on my 3rd go & that was on my old tdo5h but all of a sudden it just started to drop down to 10psi & got the sound like a sandblaster would be the best way to describe it & it only starts making that sound at around 4000-4500 rpm

[WRXONP]

could it be a fucked coil?? checked spark plugs??

[kamineko]

really need someone clued up with that vintage wrx to have a look / sit passenger. trying to diag sounds over the net is pretty arduous..

[WRXONP]

yea check the plugs and see if one is different?? from missfiring of some sort?

[rowingryan]

Hi guys ive got no intake leaks the computer seems to be all gud & same with sensors. Im thinking it may b an exaust leak in the up pipe under the heat shield.

[ben-jamminn]

If your still stuck seriously try changing your plugs man. My V4 had a similar sounding boost problem where it would just 'cut out' at a certain rpm, changed plugs and now its sweet.

Its worth a try?

[rowingryan]

Yea i just pulled my plugs out but they seem to be burning cleanly. Ill try changing them to genuine 1s & c how it goes

[ben-jamminn]

Yeah i used NGK iridiums

[rowingryan]

I jst did a compression test & got 130psi all round. Does that seem about right? & judging from the ngk site my plugs are burning perfectly. well not perfectly but u no wot i mean