Fluctuation on boost
#1
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Fluctuation on boost
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
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
#5
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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
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#12
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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
#13
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 use 3rd or 4th and get through the revs then into 5 etc to clear past the eurge
#15
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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.
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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
#18
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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
Md321h twinscroll
650 injectors
rcm trumpet & k&n filtet
full decat
2port
Last edited by peter zippy reid; 01 January 2015 at 04:10 PM.
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