I've noticed with my car in 4th and 5th if you select a high gear at low
revs and let the boost build upto its max setting, weather it be 1.2 bar or 1bar, the boost gauge fluctuates very quickly just up and down a few psi if that, but you can hear it struggling to hold the set boost limit.

I was told by the last owner the car will throw up the check engine light when the engine notices abit of knock. When this boost problem appears it also brings the check engine light flashing so the boost problem is causing engine knock.

I've turned the boost down until I've fixed the problem.

Could it be just to much for the injectors as they are at 100 percent duty and making the engine lean out? Only motorway speeds it happens.

Car was mapped by clive atthowe

 

Anyone?

 

You using an aftermarket boost controller?

 

Done via the PFC

 

I have something similar on my bug, it's down to sorting the boost correction tables apparently - I'm supposed to have fitted a new turbo by now which would have resulted in my mapper spending more time finessing it

 

Need a mapper to sort then?

 

If that's what's causing your issues then yes - mine starts in third if I floor it, but if I build up the speed/boost gradually it's fine

 

Hummm its very qerky on coming off boost say part throttle. You can only have the throttle on or off in higher gears

 

It's surge caused by standard air intake pipe. Just had the same diagnosed on mine.

Replace the inlet for a smooth silicone one job done.

 

Already just fitted a new silicone one. Already had one that looked abit rubbish

 

same here,does it sound like the air is being disturbed sort of a chopped up sound

i have a scoobyworx viper intake so maybe i should have gone for a samco/perrin as they probably a bit more sturdy

 

Mine was like this with the standard TMIC and intake and no change as I introduced a FMIC and induction kit - I haven't had chance to give it a good run since fitting a new intake hose but the only quick cure I have found was to reduce the boost

 

It's compressor surge, where at the given load point the turbo is delivering more air that the engine can take in. My 400hp 04 Sti with a vf43 surges in 5th and 6th if I floor it in low revs.
I use 3rd or 4th and get through the revs then into 5 etc to clear past the eurge

 

I'm running a vf43 on my classic. No way to fix it then other than to throw more fuel in?

 

My understanding, having experienced surge in 5th and 6th, is it comes down to the boost solinoid. Are you using a 3 port? Swapping to one from a 2 port ( and remapping) dealt with the problem. This was after AF tried to tweak the map on a 2 port with no joy. Building the boost slowly will of course help in the mean time.

 

Mine has a 3-port and it has made no difference - like I said my mapper tweeked the boost correction tables and smoothed it out quite a bit but given that was supposed to be in interim map we agreed not to spend hours playing and wait until I fitted to new turbo to fully sort it

 

Its most likely compressor surge.
Very common on vf turbos.

It can be minimised depending on boost control or by altering inlet pipe

 

Bumping old thread as i have boost fluctuation in 5th and 6th on my 03sti jdm is this surge or other issue as i have cold running problem aswell
Md321h twinscroll
650 injectors
rcm trumpet & k&n filtet
full decat
2port

 

I'm having same in my 99 uk. I've replaced all vac hoses and just fitted a fmic. My intake pipe tho has a nipple at front that's broken