lost boost again

[timucin]

dunno what happened but lost boost.
car used to peak more then 20 psi and the lowest was 16-18
but now it peaks 15 lowest is 12..
dunno what happened?!? happened right after new exhaust..
does it have to do with back pressure? or may be they touched some stuff

[img]images/graemlins/smile.gif[/img]

[timucin]

the peak boost is 10 psi now
and the car doesnt idle all the time, it stops sometimes..

[timucin]

any help....?

[markcanderson]

Check everything on this list.. then report back..

There are several reasons in general why a turbo charged car doesn't perform as it should : (i've owned previously quite a few turbo cars..)

Assuming the loss of performance isn't environmental (high temps, high altitude) and it isn't poor fuel :

1) Vacuum control lines leaking or fractured : result - turbo wastegate stays open.. only running base boost setting. Fix - Replace all old vacuum lines with new silicone lines (or OEM... whatever).

2) Wastegate actuator is leaking under boost : result - turbo wastegate stays open.. only running base boost setting. Fix - Replace wastegate actuator.

3) Dump-valve (diverter valve) is leaking (diaphragm burst) : result - engine can't lock down boost.. so boost is vented away. Fix - Replace Dump Valve.

4) Hole in the intercooler delivery pipes. : Result, air being metered is wrong.. running rich, bad idle (at worse case), smoke on acceleration.. no power.. maybe even limp home mode. Fix : Replace pipeing

5) Boost Control solenoid problem : Motor management instructs valves to open and close to control the wastegate, this is usually done through a solenoid.. can become faulty in cars older than 3 years. Result : Wastegate defaults to open and vents boost. Fix : Replace the solenoid.

6) Air Mass Meter failure : Very common failure point on a great many cars.. air not getting metered properly.. shows up usually is a huge flat spot where peak boost ( and peak torque shows up on the map..).. on an RS2.. peak torque of 410NM is at 3000rpm... so I'd expect a feeling of surging on/off acceleration around there if the AMM is faulty. Result : Car is metering and measuring intake air all wrong.. it's adjusting boost and fueling as a result... and getting it wrong for the combustion process.. Fix : replace air mass meter.
7) Lambda sensor failure.. causing a loop back failure on the fueling/air/boost mix.. Fix: Replace sensor in downpipe.

Now getting into the expensive reasons :
Fueling problem.. perhaps injectors are faulty/dirty.
9) Head gasket problem.
10) General engine issue
11) Turbo seals
12) General turbo turbine failure

[markcanderson]

Also, since you have effectively zero back pressure.. perhaps base boost needs to be adjusted ?.. this was done on my Saabs with slightly shortening the wastegate actuator rod.

[timucin]

copy - pasted everything : will check tomorrow morning and tell the results
[img]images/graemlins/smile.gif[/img]
thnx

[timucin]

-damaged hose
[img]images/graemlins/smile.gif[/img]
found but no spare part,will try to repair it on monday