J57ltr 
Ok so I am going on almost 2 months of troubleshooting this car (05' GTP) and I am not getting anywhere. I am stalled. I can see all kinds of information but it doesn't make sense.
Car was bought with 3.4" pulley, slightly better exhaust. I replaced the plugs and wires with new stock wires. The car originally had a multi cyl misfire. Replaced that and the car would lay over as it was lean, loss of power. In trying to solve the problem. The car will not develop any boost most of the time (to 5psi occasionally then drop to 0").
The car goes dead lean and backs timing to negative values at times under full throttle. If I stay in the throttle it will just lay over and after letting off the car goes into Reduced engine power, drops ABS and sets timing at 15* ATDC and dead rich. It will also allow small amounts of throttle input then drop out let off and it allows a little more but soooo little power. When you stop it cuts the accelerator pedal out completely. Turn the car off, open the door wait a few seconds close the door and restart like nothing happened. Usually gives an P0068.
things I have tried:
Added mechanical boost gauge.
installed 3.8" pulley
replaced baro
replaced map
installed stock airbox properly
checked all vacuum lines using a hand vacuum pump
replaced vacuum lines and used Ty wraps and a Ty wrap gun
cleaned TB
replaced MAF (Delco)
removed SC and sealed off TB coolant passages and RTV'd the SC back on because no gasket available
(did find loose SC bolt on forward side of SC and gasket compromised)
Tested fuel pressure over 3 days, consistent 65 psi
Replaced both knock sensors (due to KR at all levels of throttle and random)
Other things I have tried:
scanned using T app and timing backs sometimes to 12-14* and others to 0* 02 drops dead lean. Plugging the BBV causes computer to command less throttle than demanded and limits boost to 0 and causes Reduced power mode.
If I can read KR it won't let me look at timing or 02 or anything else of value but when I did after replacing the knock sensors I get 1-2* sometimes it mostly at shifts or when coming out of lockup, I think you guys call that burst knock or something.
anyway if someone knows of something that would help that'd be great.
I am wondering if someone tried to reprogram the computer and screwed up. The car runs fine in NA mode and I just don't know what else it could be.
Edit: most of the time it runs great NA mode, but every once in a while it stalls when taking off and goes dead lean and 0* timing and 0" Hg trying to accelerate at a slow pace. Actually have to get on it to get going.
Also if I do a 1-2 run at WOT and it sets the P0068 it also sets a Low 02 output. Scanning it will go dead lean and the 02 stops switching if I press the gas lean let off rich. I have to stop the car open the door turn the car off wait a second and start it back up. The. It switches normally.
thanks,
Jeff
