hey, am wondering if my vsv has an issue, normally my car would build boost slowly to 12psi in 2nd gear+, only reaching 12psi at about 6000rpm upwards.
but yesterday I did absolutely nothin to the car, and it begins running 14psi, boost needle shoots right up to 14psi and soon as I get on the gas.
Is this a problem? any info or advice is appreciated. Its is basically stock with an HKS intake, gutted cat and a 3" exhaust from midpipe back.

maybe a leak in one of the vac lines between the TVSV and the wastegate actuator?

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Whats strange is that it only happen every couple a days, its not steady 14psi, this mornin i took it out for a run and it stayed at 12psi :S

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Sounds like something funky is going on with the tvsv.

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So what you think I should do?

well stock is 12, so on the days when it is running 14 drive it like ya stole it.

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Ha ha oh definately lol exactly what I do.. Pulls like a monzter with jus 2 extra psi

It can vary.


Just keep in mind the magical figure is 10psi. Thats the wastegate spring in a CT20b.

Boosting in excess of 10psi is normal due to the TVSV bleeding air off back into the idler piping it should be 11psi 1st gear, 12psi 2nd gear, 13psi 3rd+ gear

When my turbo suddenly went from 13psi to 16psi I knew I had problems with the turbo.

I think it's due to the wastegate being so small it can't relieve enough pressure for varying conditions and in my case having an upgraded turbine and compressor wheel.

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Currently I think my TVSV is not functioning though, its running steady 10psi and take forever to reach 10psi like only at 5-7200 rpm no matter the gear.
You have upgraded from CT20B to what turbo?

CT20b is a very responsive turbo by nature and the 10psi boost threshold begins at around 2500 to 2800 on some st205s depending on their condition

if its sluggish for you then theres something wrong with your turbo, either a boost leak (check your clamps esp the throttle body to IC clamp) otherwise perhaps the turbo itself is playing up.


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When my CT20b shredded itself the turbo company sent back a CT26 with the most common upgrade which uses td04e parts or similar, either way it gives u a steel shaft and turbine and somewhere in there is mentioned 46mm im not sure if it refers to the compressor inducer or the turbine exducer.

their reasoning was that there was no ct20b available at the time and mine was not in a repairable condition (?)

I think there is probably a problem with my wastegate though, ama get it tested soon, because when it does 14psi, it hit 14psi by about 4000rpm tops, and turbo response is rediculous. but currently it starts building boost very sharply but slows after 7psi and slowly climbs to 10.

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I dont understand? So is it responsive or not? If it swings up to 7 immediately its responsive, if it doesnt then it's not.

Swinging up to 7 and creeping up to 10 and hanging around there does sound like the VSV, so maybe its time u ditched the VSV and got a boost controller?

Because the wastegate is sprung to 10psi, it makes sense to hit 7 and creep up to 10 (that's wastegate creep, normal) but the not going past 10 part is the VSV not functioning, but as I said before double check leaks esp the throttle body clamp

Ok, It is responsive it max at 10psi majority of the time. But tonight I did a few pulls i got 11psi in first and 14psi in second onwards :S... but stopped shortly after. It seems to cut to 10psi after the engine has been running for some time. The pulls were done just after the engine was at normal operating temp. But after no boosting for a little while back to 10psi. I am almost now certain there is somethin going on with the tvsv. But I am also wondering if there is a reason for its behaviour, seeing that it has been known to limit boost depending on how comfortable everything is.

Checked for codes?

Sometimes you'll have a code 54 to clear even though the CEL light doesn't come on

it has no codes..