Po170 engine code (fuel trim malfunction)

[Cjlancer]

I have a 99 GSX. evo 3 16g@13psi daily , 255 walbro, stock injectors (got 550cc at the house but just waiting for my SAFC2 to come in, injen intake, 3" all the way 3" racing cat,hks Bov,evo 3 manifold. got the taylor racing thunder volt racing wires 10.4 mm and NGK iridium spark plugs. etc

erase the code and drive for about 40 to 50 miles and the Engine light comes on. i have no missfire but every once a while i see a little bit of black smoke. the top O2 sensor has been changed but the bottom one still stock. my car gots 65,500 miles on it. car runs perfect no missfire or nothing no hesitation. nothing. what coulde that P0170 be ohh and then last night it came up again went to autozone they told me po170 erased it with there OBD and drove for 7 miles and it came back up. please help me out here. it says to check: 1- volume air flow sensor output frequency, 2-fuel presure 3- intake air leaks 4-engine coolant temp sensor 5-intake air temperature sensor 6-barometric pressure sensor 7-O2 sensor( bottom one still stock) 8- exhaust manifold cracks(i just put a brand new evo 3 like 250 miles ago.) what could it be

ohh just tought of it would the HKS SS BOV dumoing to the atmosphere do something.?

HELP>>>>>>

 

[psychlow]

If you're running a Walbro 255 without an AFPR (aftermarket/adjustable fuel pressure regulator), I would be willing to bet this is your problem. If your base fuel pressure is too high, your car may be bottoming out your "LO" fuel trims in an attempt to level out your oxygen sensor readings to no avail.

A logger and a few runs could give you a bit more to go on.

EDIT:

Other things to check:

-Exhaust leaks. (I know you put a new manifold/turbo on). Try checking for leaks by taking out a plug, dropping a *little* oil in one of your cylinders, replace the plug, and start her up. Rev her a bit at idle, and watch your engine bay for escaping smoke. You could be leaking from your exhaust mani/turbo inlet/O2 housing inlet gaskets.

-Intake leaks. If you don't yet have an intake pressure tester, make one and try it. Even with a 99 GSX, you may be surprised at how many leaks you have.