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Discussion Starter · #1 ·
Hi,

I bought a 2007 9-3 1.8t a few months ago and it has an issue where after the car has had a chance to heat soak (such as stopping to go into a shop or in stop start traffic), there is no boost at all. Once the car has ran at speed for a while the issue clears but it’s rather annoying. When the issue is happening, boost pressure is at around 0psi even under high load and high engine speed. The garage has had the car twice and haven’t worked it out. They’ve replaced the throttle body and adjusted the brake switch. Neither I was convinced by but the car is under warranty so not my cost.

Has anyone experienced this before and any suggestions? I was thinking of replacing the boost control valve as that seems logical but open to the experience of others.
 

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Hi,

I bought a 2007 9-3 1.8t a few months ago and it has an issue where after the car has had a chance to heat soak (such as stopping to go into a shop or in stop start traffic), there is no boost at all. Once the car has ran at speed for a while the issue clears but it’s rather annoying. When the issue is happening, boost pressure is at around 0psi even under high load and high engine speed. The garage has had the car twice and haven’t worked it out. They’ve replaced the throttle body and adjusted the brake switch. Neither I was convinced by but the car is under warranty so not my cost.

Has anyone experienced this before and any suggestions? I was thinking of replacing the boost control valve as that seems logical but open to the experience of others.
Have any codes / check engine lite on?
 

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there are 2 valves one on the inlet manifold other on the turbo..they look the same but they are different,hence 2 part#..
 

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Discussion Starter · #5 ·
So, thinking of the failure modes of both; if the boost control valve was stuck open, the turbo would overboost, if it was stuck closed, would I still see base boost? If the charge air bypass valve stuck open, I would see no boost and if the charge air bypass valve stuck closed, the turbo would still boost but not blow off on open throttle.

If it is a valve, it would suggest the charge air bypass from this logic? I'm just a little at a loss why I have no EML on for it.

Are these valves controlled proportionally or are they either off or on? I'm wondering if I could rule out the ECU by checking for a supply voltage when the issue is occurring.
 

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So, thinking of the failure modes of both; if the boost control valve was stuck open, the turbo would overboost, if it was stuck closed, would I still see base boost? If the charge air bypass valve stuck open, I would see no boost and if the charge air bypass valve stuck closed, the turbo would still boost but not blow off on open throttle.

If it is a valve, it would suggest the charge air bypass from this logic? I'm just a little at a loss why I have no EML on for it.

Are these valves controlled proportionally or are they either off or on? I'm wondering if I could rule out the ECU by checking for a supply voltage when the issue is occurring.
It is odd that you have no codes for this.
Make sure your battery is good and the connections are clean and tight.
You could do voltage drop tests from the battery to the engine positive and grounds.
I just found some resistance on the big positive cable of my 2.0T.
 
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