Join Date: Feb 2005
Location: Zionsville, Indiana
Cause of minor reduction in power/boost?
So this is one of those things that was minor enough I never really put much thought into it until now, but I'm curious.
I have a 2009 GXP with the GMPP Stage II tune that was professionally installed. It's all good. When I first got the car back in 2015, it was a bat out of hell and it wasn't terribly difficult to hit 22psi of boost. I think I even hit 23. I don't know if it was overnight, because I don't run it that hard often, but about a year or so later, no matter how hard I push it in 3rd or 4th gear, I cannot break 18 or 19psi, and the car just feels like it's missing that edge it had when I first got it. Aside from general maintenance (water and fuel pumps, cam solenoids, tires, oil, etc) and a stereo system install... I'm not sure I touched anything that would cause this.
Is it possible for a tune to revert to stock? There are several time I had the battery disconnected for days, but I can't imagine that would cause it. Is there a sensor or sensor that could go bad to do this? Any other things I should look into to see why I am being robbed of boost and HP? I cleaned the MAF and air filter, but that didn't change anything. Any help would be appreciated — I want to exhaust all reasonable options before get getting a Trifecta tune and see if that takes care of it. I was absolutely happy with the GMPP tune.
Also, possibly related... possibly not... but my gas mileage isn't as good as it was early on, either. Probably about 40-60 miles less per tank than I was in 2015 with similar driving habits.
Last edited by Fortimir; 03-27-2019 at 12:16 AM.