2002 Ranger check engine light

i have a 2002 ranger with a 4.0 litre,check engine light comes on, i get codes of p0174 & p0171 the codes are bank 1 & 2 system lean.what are the ideas for me to check first? any comments will help.thank you

Just happened to have the same CEL code in my '99 4.0L engine a couple of months ago. The code indicates that your PCM is sensing lean mixture in both banks. You have two 02 sensors before the cat and one after. The possibiity that both 02 sensors are bad is lower than the possibility list. So what is affecting it is common to both banks. My problem was a leak in the upper intake air manifold. While idling, I squirted an injector cleaner compound in all possible areas of vacuum leak and found a section whereby the "O" ring gasket leaked. Bought the gasket from Ford ($15.00) and replaced it myself, the CEL has not gone back thus far and my gas mileage improved a bit. So check this out and then go from there.