Overboost Plus Flat Spot In Boost

[ur.a.bus]

i got a service a couple of months back, car is standard 99 uk turbo and was running fine before the service.

since getting it back i noticed rather than boost at 0.8 it's reading 1.2, there also feels like a flat spot in the boost.

when the turbo kicks i feel the boost then it drops for a sec then goes again.

i have checked the 2 small hoses with the "t" and the longer 1 that goes to soleniod for leaks and they seem fine (after getting advise in technical section), i have done alot of searching on the site and found if the actuator is stuck closed this could cause overboost.

the turbo also makes a chattering noise at 300rpm for a sec, not sure if i am imagining it or not but turbo also sounds louder when spooling. (air noise?)

could this be my problem and if so how do i fix/clean this?

any help much appreciated as this is really bugging me and i no longer have faith that dropping gears will get me past slow moving vehicles

[scoobnoob]

I've had what sounds like a similar problem twice with two different cars, an import wrx and an import sti RA. Both needed new coil packs and spark plugs

[stuarted]

check your air intake pipe for splits where it joins the turbo, mine was split on the underside and gave similar symptoms

[Big 'D']

I've had what sounds like a similar problem twice with two different cars, an import wrx and an import sti RA. Both needed new coil packs and spark plugs

You had overboost with a spark issue? That is highly unlikely mate, the things you should be looking for as the wastegate is controlled by the air produced by the turbo are, blockages, kinks or splits in the complete wastegate pipework between the turbo and the wategate solenoid, you can test for wastegate failure by plugging the outlet nipple directly to your wastegate actuator nipple and going for a run the turbo should only run wastegate spring pressure in this setup if it runs higher than this to overboost your actuator is goosed, or you have boost creep. Another thing that would cause overboost is if the restrictor pill in the short piece of pipe between the 't' piece and the turbo is the wrong size (too small) or incorrectly situated ie on the other side of the 't' piece.

If the wastegate solenoid was to be stuck open this might also cause the car to overboost, it might be worth giving it a clean anyway.

Let us know how you get on

Cheers Iain

Edited October 17, 2009 by Big 'D'