Most of us are spending money to boost that high, you got it free !!!!

Seriously, I agree with you something is up. Perhaps they will reflash it for you, could be a computer glitch.

 

No, it did a bump, limited the boost and threw the over-boost code. They called again and said they are only seeing 20-22 now on the gauge which is correct. I asked if they looked at the boost valve and they said no but if I wanted to pay for it they would. I can do that myself. GM isn't going to authorize any warranty work unless they can see it broken. If it's working correctly now, they won't. I get that but arguing any more is futile.

So I will likely get it back today and take over the problem. This isn't my first boosted engine but this particular turbo is new to me. I'll pull the valve and see what the diaphragm and spring looks like.

 

Update - I got the car back. It decided to work correctly (20-22 PSI of boost) and they couldn't get it to overboost again. They gave me the coffee cup logger to run for awhile to see if I can catch it when it goes goofy. So far, squat. One thing I notice is that it seems to overshoot a bit more than it did before it settles back but it might just be me paying more attention to the boost gauge. If I can't get it to fail in the next two weeks all I can do it watch it. Runs fine. Can't complain.

 

That is the rule, these cars are a little weird, glad it got scared of the mechanics and is running right....

 

Well today I was cruising along and felt a very slight bump in the engine. No CEL but there was no boost. Ran fine otherwise (no big power though). Figured I'd get it to work and look around (maybe 2 miles). I had to go up a ramp and found I had boost again. It's 100F here and I was thinking maybe a pipe split or started leaking? Weird. Seems fine now. I'll watch it going home.

 

So your car was over boosting a year ago and it fixed itself? It's been running fine ever since until now? Odd. First thing I would check would be the watstegate actuator rod to make sure the nuts are tight on the rod. Then I would be looking at all the related pressure/vacuum lines. Some have reported a small crack on the wastegate nipple. Maybe the ECM has "learned down" the over boost. If so, You could try to recreated it by pulling fuse #41 under the good which resets the ECM.

 

I really should have posted in a new thread since the problem is different.

I'll start a new thread.

 

And we're back!

Getting the overboost again. No code set or pending but it's hitting 28 PSI. In October I removed the wastegate diaphragm and checked it and it looked fine (when I got the underboost.)

I need to jack up the car and look at the wastegate rod and nuts and the solenoid. It's consistently hitting 28PSI so hopefully the failure is solid and I can find it. At part throttle it holds the boost at 5 PSI like normal but when you roll into the throttle it will shoot up. It appears it's trying to limit it but I don't keep my foot in it long enough to see if it will pull it back. It certainly doesn't for the 2 seconds I allow.

I wish the wastegate solenoid and rod could be accessed from the top. Maybe I can feel the nut position.

 

Wastegate diaphragm? I think you mean the bypass valve. Bypass valve will not cause over boost, only the wastegate and related components. You can visually inspect the wastegate rod nuts from underneath and there is room to teach ur hand up there too. The wastegate solenoid AKA boost control solenoid can be accessed from the top. It's on the same side as the bypass valve with hoses and wiring connected to it. One of the hoses goes directly to the wastegate canister so check all related connections. Depending on how much $ the boost control solenoid costs, it may be a good idea to just replace it.

 

Yeah, I mean the bypass. I'll check the canister and hoses. Too bad this level of boost isn't factory! :)