05chevy that wont run???

well here it goes ive been working on a 05 chevy its a 5.3 tune long tube headers 3 in exhaust knn 373 geers and a 4l65e tranny it will run 85mph and a max speed of 95 mph with tune a best et 16.9 dont know whats wrong with it any suggestions

Who tuned it? What is the fuel pressure? Stock cam? If so where does it shift? Any problems on the road (misfires, etc.)? Trans slipping? Converter dead? Electrical system in good working order?

i bought a used computer and just unlocked it so its stock but it still fills the same as if it was tuned and the computer was on an 11 sec truck also put injectors it doesent even make burn outs the check engine light is off no misfires no fuel problems shift good stock cam

damm bro that sux,when my truck didnt want to burn out it was the knock sensors.but in your case,im not sure,good luck,check with file.

Used computer? Are you sure it's the right one for the correct engine and trans?

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Originally Posted by GasGuzzler

Used computer? Are you sure it's the right one for the correct engine and trans?

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yea it was unlocked by tiburon stock and he set the truck's settings

Did it run fine before the tune? Not trying to point out the obvious just saying if it ran before the tune the one your running now is prolly the issue.

I'm going to guess it's the headers making it fall on it's face. Especially if its an L33 with the higher compression.
Your going to need to bring the pipes down to 2.5" and put some cam in there.
I have seen 5.3's with a magnuson super charger fall on their faces after adding headers and then wake up after they were removed.
Headers on theses new motors are a different story than the old 5.7's and such. When you open up the flow on these motors you had better have something for it to push.

You have flown yourself out of some torque.

Gotta be that PCM, I'd say 50-70 percent of the people on here have LT's with no problems.

sounds like you need a better tune, or a new pcm.