Boost problem, please please help!

I have a mark iv 1995 tt. Since i bought the car i have had different boost readings when the car has just warmed up and into 15 minutes of driving. It has a K&N induction kit and total decat stainless steel exhaust. I have fitted a FMIC and changed practically all of the thin vacuum pipes. The pressure reading when engines just warms up is 14psi and then it drops to around 10psi after 15 minutes or so!! then it remains low until the engine has gone cold again

Hi, I had a very similar problem and it turned out to be one of the vsv's, have a look through this section here;

http://www.mkivsupra.net/vbb/showthread.php?t=35926

pics of valves etc

http://www.mkivsupra.net/vbb/showthread.php?t=35924

to get an understanding of the vsv's, then start the car and inspect that the IACV vsv functions the actuator while revving the throttle in neutral(you should see the rod from the actuator move up and down) then inspect the EGCV actuator and make sure that the rod moves from left to right,normally you need to rev the car quite high to see this, maybe 4k or more, if neither of these are the problem then post up and we'll go from there.

Mine was the same though as the first couple of runs in the morning the car would hit full boost and stay there but after that it would just drop off to 0.7 bar and would just be using the 1st turbo till the next time I started up from cold.

Hope this helps

Tom.

Cheers for that ill look into it and get back

Baz, is it UK or Japanese import Supra? If it's a J-spec with both cats removed and aftermarket exhaust you should be seeing much higher than 14psi (1bar ish).

Are you sure both cats have been removed and is it UK or Jap Supra?

Are you sure both cats have been removed and is it UK or Jap Supra?

I Knew there was something I needed to ask!

Hi sorry for the late reply. It's a Jap spec. I must admit it does go over 14psi as the fcd kicks in. Im thinking of installing an Apexi Avcr to make sure I don't overboost??? Both cats are out for sure. Once I have solved the present problem I'll have to have a FCD fitted and then possibly the EBC. Not sure where the best place to buy VSV's is?? any ideas guys? dealers maybe too expensive....

Hi sorry for the late reply. It's a Jap spec. I must admit it does go over 14psi as the fcd kicks in.

Not sure what you mean there, do you mean fuel cut kicks in and you get the hit-a-brick-wall effect?

Im thinking of installing an Apexi Avcr to make sure I don't overboost???

Alas, boost controllers can only increase boost, not lower it. You need a restrictor ring, Chris Wilson makes and sells these, have a search on here for them

Both cats are out for sure. Once I have solved the present problem I'll have to have a FCD fitted and then possibly the EBC. Not sure where the best place to buy VSV's is?? any ideas guys? dealers maybe too expensive....

A lot of people who have gone single turbo should have VSVs lying about the place. They got for ) I'd help but I just sold all mine this weekend

-Ian

mate,

A boost controller can increase boost but not decrease your current boost. You'll need a restricter ring fitted in the exhaust to keep it down.

I have the restrictor ring in also. I do get the hit the brick wall effect. I'm searching for VSV's and then Ill fit a HKS FCD chip. I want to raise boost to 17psi with an EBC??

As you said Tom

in my case there is slightly no boost and i've checked the IACV & EGCV rods they are moving up and down

non of the both turbos spinning in !!!!!

Hi, I had a very similar problem and it turned out to be one of the vsv's,

Tom, what your specific VSV problem? was the problem fixed by replacing the VSV?

Tom, what your specific VSV problem? was the problem fixed by replacing the VSV?

yeah the IACV VSV stopped working, due to age no dought, soon as it was replaced all was good again

Interesting. I've had the same sort of thing a few times where the boost seems to drop off slightly as the car warms up. All fine at the moment, but I wonder if one of the VSVs is on the way out.

cheers