Losing Boost!! 2012 GT500

[GeigerZ]

There was a thread posted several years ago on this forum, but unfortunately, the OP didn't respond with the fix.

http://www.svtperformance.com/forums/showthread.php?784416-2011-GT500-boost-dropping-off

I just picked up a 2012 GT500 with 14k miles on it and have the exact same issue as the video below. Yes, my foot was mashed to the floor as well.

[video=youtube;bHe808NqIPg]http://www.youtube.com/watch?v=bHe808NqIPg[/video]

Only mods:

2.5 pulley
90mm idler
Borla Touring Axleback

 

[nxhappy]

could be the belt slipping. Do you hear any noise? Is there belt dust on the S/C snout ?

 

[Justin@VMP]

It could also be fuel trim learning getting applied to the air model, would be nice to do a full datalog on it with fuel trims (short and long, bank1 and 2), along with load. If the car is not falling off, all the boost may still be there.

 

[kozumasbullitt]

Do you have a tune on the car? I didn't see a tune listed in your mods or a mention of a handheld.

 

[LEXiiON]

It could also be fuel trim learning getting applied to the air model, would be nice to do a full datalog on it with fuel trims (short and long, bank1 and 2), along with load. If the car is not falling off, all the boost may still be there.

Hi Justin. That sounds interesting. Can you explain this a little bit further? I always thought, that at WOT it would take the fixed values (open loop) ?
Mine always goes 0.0 on STFT and LTFT bank 1 and 2 when at WOT, which led to believe me that is true.

Thanks,

LEXiiON

 

[GeigerZ]

Handheld tuner will be here in a couple of days with a few tunes.

Going to hold out until then to see what happens (better/worse or no change) and to data log some WOT pulls.

So odd that the RPM's are headed up and boost headed down @ WOT.

Forgot to mention that if I'm in 2nd and punch it - stumbles, misses and spurs needed to ride it. If I slowly get on it in 2nd going WOT, it seems to be ok, but redline happens too fast to see if boost drops. Same with 3rd... get the RPM's to 3500, punch it - it sputters and stumbles. Ease into it and it's like the video posted above.

 

[GT Premi]

I thought it was normal for boost to roll off at the top end of the rev range. I haven't always paid it much attention, but I just recently noticed the same thing with my car. I was at WOT and in the triple digits. I glanced down and noticed the boost gauge had dipped down to around 10 pounds or so. The car was still pulling, so I didn't think too much of it at the time. I was just a little concerned later, though, because I had never noticed the boost gauge dip before. All times before that, whenever I glanced at the gauge during WOT, it seemed to stay pinned at 15 pounds.

I'll be watching this thread to see what the pros say.

 

[nxhappy]

Handheld tuner will be here in a couple of day with a few tunes.

Going to hold out until then to see what happens (better/worse or no change) and to data log some WOT pulls.

So odd that the RPM's are headed up and boost headed down @ WOT.

Forgot to mention that if I'm in 2nd and punch it - stumbles, misses and spurs needed to ride it. If I slowly get on it in 2nd going WOT, it seems to be ok, but redline happens too fast to see if boost drops. Same with 3rd... get the RPM's to 3500, punch it - it sputters and stumbles. Ease into it and it's like the video posted above.

so you swapped the pulley, and kept the stock tune ???

 

[GeigerZ]

so you swapped the pulley, and kept the stock tune ???

Yes, the '12 can and should adapt to the new requirements (or so I was informed). I have my doubts though and will know soon enough with the custom tune if some of the issues go away. Meaning that the throttle stab miss and stumble should be gone, but thinking the boost loss might be physical or could be the TB closing by wire.

 

[nxhappy]

Yes, the '12 can and should adapt to the new requirements (or so I was informed). I have my doubts though and will know soon enough with the custom tune if some of the issues go away. Meaning that the throttle stab miss and stumble should be gone, but thinking the boost loss might be physical or could be the TB closing by wire.

I always thought more boost means a new tune...... Is the stock MAF sensor and computer capable of correcting everything for the extra boost ? Seems irrational .

 

[scotsam]

From what I heard 11-12. cars can deal with a pulley change without a tune. I think it's due to frequency based maf ,knocksensors and widebands. Obviously not optimal but supposedly safe.

 

[scotsam]

On a stock supercharger that is and not a 10 or 15% lower either.

 

[dirtyo2000]

Seems like your playing Russian roulette with the motor but I could be wrong

 

[nxhappy]

Seems like your playing Russian roulette with the motor but I could be wrong

exactly. at least data log it and see WTH is going on . A tune is a lot cheaper than a blown motor.

 

[kozumasbullitt]

The smaller pulley is allowing the capability of spinning the blower faster. Is it possible that more air than the stock tune can handle is being pulled across the MAF? I also know that the OEM boost gauge uses the MAF to calculate boost, are you sure boost is actually being dropped off?