Well i just got my gsr-t together and i am tunning on crome, im tunning 10lbs and past 4500 i just cant seem to get a steady afr`s, in boost to 4500-5000 rpms i got it to run great 11.5-12.3 afr all across almost perfect, but after 4500 it just completely leans out, creeps to 13`s 14`s and 15`s no matter what i do, i heard the stock fuel pump was good till 300hp, i know with the right timing i am probably pushing near or over that but, why would it start leaning out at 4-5k, is it because the torque is starting to peak out?? I remember somewhere hearing thatpeak torque usually starts to demand the most fuel. Now please do not give reponses saying buy a fuel pump i already have a 255lph on the way i just wanted someone to clarify why it would at such an early rpm, I dont understand that my fuel pump has 200k plus miles and its not designed for 300hp.
Ryan

 

more then likely your fuel pump is cutting out...if you have a fuel pressure gauge..you can monitor the pressure, see if it drops...if its not in cabin...maybe you can somehow rig it to your windshield temporarily and monitor that while driving..would help to have a buddy go with you...

but if it drops..fuel pump is not keeping up!