Just turned 22,000 miles tonight, have had the Hahn Tuner since 9,000 miles, and my previous threads & posts about the tuner still stand....IMO a great product if that is the way you intend to go.
But awhile back, I had noticed and posted about the boost when engaged in
3rd gear (AUTO) would seem to surge back & forth or spike as you accelerated hitting partial passing gear, not WOT passing gear.
Thought it was just the nature of the beast, along with talking to Eric, with all of his info, and I thank him for that, I now have corrected the boost spike mentioned above. And it was so simple, and it applies to any engine, regardless of mods, tunes, or what have you, and it's called "PM" (Preventative Maintenance)....Remember back when I did not check the coolant recovery tank fluid level for many months, well I also failed in checking the tightness of the T-Bolt clamp on the IC piping above the turbo. I have been checking the clamp behind the air box, but never thought to check the T-Bolt, thinking that it was tight from the factory, after the way they put my SS together, what ever made me think that???
Well that T-Bolt took 1 1/2 turns to tighten up and guess what?, the boost spike is gone, now when I press on the accelerator in 3rd gear, the response is instant, no spike, no lag, no surge.... I am a happy guy....
This also eliminated the erie, high pitched sound I started to have in the AM, especially when the engine was cold, as you let your foot off of the accelerator. As soon as you press down, the noise disappears, appartently it was sucking air in at that connection. I know some other members also have this noise. check that T-Bolt clamp.....
And you would think that with all of the cars I have had, I would have learned my lesson about engine operation and the vibration that results from that, to do a more thorough PM like I used to in the past....Even at my age you still live & learn..........

 

I'll have to check this too. I have noticed this surging back and forth at that point. It's with a steady accelerator and just before the shift point. The boost would go from about 14-9 up and down. I just thought it was the GM tune and was natural. Push on the accelerator more and it goes away. I'm not sure if its the same erie sound but I have a high pitch whissle when I let off the accelerator again thought it was natual for a turbo. Time to check it's in the shop today for it's 2nd oil change - 0% at 20,544

 

I have mine in the shop for an unrelated problem (parking brake cable came loose and was rubbing on wheel). I mentioned the boost would randomly jump around and showed them the bulletin on the lower TMAP sensor being mounted wrong. The tech checked that and said it was mounted properly, but found and "issue" with the charge tube, and ordered a new one. I haven't talked with the tech yet, but will see if I can find out what the issue is/was.

 

the high pitched sound is back, further investigation is needed.........

 

upon further investigation it has been determined that the lower plastic tube going into the turbo also needed to be tighten. This was discovered during replacement of the BOV spring. The high pitched sound is once again silenced. We shall see............................................... .

 

Update:
Tech "found leak at vacuum hose nipple on charged air pipe between IC and TB".
Replaced charged air pipe.
No more surging and have seen a consistant 22 lbs boost at full load.

 

well good deal guys... get on top of that maintenance Tom...

 

Eric, you call it maintenance... Once the clamps are tightened properly, are you saying that you need to keep going back and re-tightening?

 

yeppers, they get loose just like anything else, not suspose to but Newtons law comes into play

 

GM should add that to the maintenance schedule