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Discussion Starter #1 (Edited by Moderator)
Hey guys newbie here again. I have an overboost problem. Long story here, sorry. I cleaned out my intake and EGR, new VNT actuator and double checked on rod position, new MAF, new vac lines, double checked N75 valve. I started out by cleaning the EGR and intake and got a P1556, underboost or negative deviation code. From the bad actuator, changed it out. Now Im getting an overboost code. Like I said, I've changed all those things out and double checked the others. The car runs great in town, get her up to 3000 Plus RPMs and runs great. Get on the HYW and do about 60mph and 2300 RPMs and she goes into limp mode with overboost code. What is going on? The turbo kicks in nice in town and pushes me along very well. So why the overboost? Any help would be great. Could it be the oil in my intercooler pushing through my intake? I noticed there is some oily goo in the intake again, hopefully from the intercooler. Would that cause this? Is the sensor in the intercooler the MAP sensor? If thats oiled up would that cause the overboost? Im out of ideas? Please help.
Thanks all.
I forgot to mention, I have a race pipe installed not the EGR. Have a small tune as well only 20 more HP over stock with EGR Delete with the tune. Was suppose to be ok with the setup on my car. Like I said all vac lines in order too. Lost for overboost code now.
 

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Sounds like you might need to clean the actual turbo vanes maybe. No idea about a sensor in the intercooler. I've never seen a sensor there.
 

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Discussion Starter #3
Well I thought about that, but didn't think there were stuck or that dirty because the turbo seems to work well from dead stop through the 4th gear running her up to 3000 plus RPMs. Pushes along real good, just dies down in fifth at about 60mph and lower RPMs. I guess I could try. I hate to take the turbo off though.
 

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If you've been through the faq and that hasn't solved it I don't really know what else there is. You could wait til later and see what others have to say, I could be missing something.:)
 

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Discussion Starter #5
Cool, well thanks. If you happen to find something out, please let me know. This has been a real helpful forum so far.
 

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Yes, you're overboosting and it sent you into limp mode. That's what the chart shows but you already said that :)

Take a look through the limp mode trouble shooting article. Overboost is normally vac lines, N75, sticking vanes or actuator.
 
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