Help Explain This Turbo Fault Please

[BSK]

when i hit full boost at 1.2bar it cuts and pressure drops to about 0.6-0.7bar then re spools up then cuts then re spools etc....at full throttle. it wont hold it there

its happened 2 out of the last 4 nights. problem seems to go away then come back again.

its on an r32 gtst with gt2530 fmic afc2 ebc... has also happened on the lower boost settings. have checked all the vac hoses and connectors.

anyone experience this before??

[monk]

what kinda boost controller?

sounds like its playing up

[1400r]

fuel cut?

[BSK]

what kinda boost controller?

sounds like its playing up

<{POST_SNAPBACK}>

its a blitz dual sbc

fuel cut? would the afc cause that?

[traphead]

I seem to be having a similar problem, and we cant come up with a solution at the moment. Car is at the mechanics now.

I just had a gt3040 with a .48 exhaust housing installed and it is having these same symptoms on the dyno. Boost gets cut when it reaches full boost and then spools up again. This occurs with and without the boost controller in the loop. And also occurs with different sized actuators. It seems like when the wastegate opens it doesn't close quick enough hence causing the drop in boost. When the waste gate eventually closes the turbo spools up slowly (rather linear) if running low boost, but spools up quicker at high boost then drops boost again when it reaches full boost.

The wastegate doesnt appear to be sticky either (BSK you might want to check this on yours as it could be the problem, especially if it only occurs sometimes).

The back pressure in the manifold is being checked today. Some people think that the GT3040 with a .48 is too big of a mismatch (compressor size in comparison to exhaust housing) and is causing the wastegate to do funny things. But, gcg assure me that they have sold plenty of these turbos for 2L engines and have never had a problem.

Any ideas?

[BHDave]

The dsbc has a boost cut function. This has a peak boost where the cut happens and a duty that the solenoid drops to for a second or 2 before going back to normal.

If you have set your gain too high then it will spike, ebc goes "SHIT! better cut this" it drops it down to nothing for a second or so then tries again.

I would be looking at your boost cut settings as they are probably set very close to the max boost you are running so a cooler night will allow you to overboost and also the duty reduction setting as it sounds like it has been set pretty high, drop it back to 5 or so.

the screen will flash red when it over boosts and it will beep at you.

All this relates to the old dsbc by the way that only has one level of boost cut and one gain setting, the newer ones have multiple adjustments for each setting so you may find you're boost cut in the low setting is too low as well?

[BSK]

Sorted!!!

gain was set way too high on the dsbc...around 80. brought it down to 30 as per user manual and i got a nice clean spool curve rather then it shootin straight up n bouncing off the limit settings.

cheers BHDave !!

best of luck with your problem traphead.

Edited February 1, 2006 by BSK

[BSK]

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