97 Explorer V6 4.0 p0171 & p0174 HELP!

So on my 97 Explorer i keep getting codes for banks 1 & 2
too lean. I have tried searching for vacuum leaks with
a smoke machine and found nothing. I changed the fuel filter
and no change. I hooked up a scan tool with live data and saw
my fuel trims were all at -100 and all 3 o2 sensors read 0 voltage.

What is the problem with my Explorer?

Sohc v6?

If you have the SOHC V6 engine this link may help: Lean condition procedure

Many scanners are unable to read the Explorer fuel trims and O2 sensor voltages. If you warm the engine, clear the codes and they don't come back until a cold start then I suspect you have leaking intake manifold gaskets.

I believe mine is the OHV V6 not thr SOHC. I thought that if i used
a smoke machine on the intake that i would find if it was
leaking or not. Are all those lean condition tests for the SOHC
will the work the same for my OHV?

OHV V6 lean

I have no first hand experience with the OHV V6 (vin X) but the TPS test procedure, the MAF sensor test procedure and the fuel pressure test procedure should apply. The OHV V6 is less susceptible than the SOHC V6 to intake gasket leakage but it stlll happens.

its the oring gaskets under the upper intake they shrink after awhile and no longer seal ,then it throws those codes .,been there done that .
you may notice a bad idle when engine is cold that gets better as it warms up too .
the orings shrink when cold creating the leak ,they swell when warmed up and idle gets better ,but there comes a point when no amount of heat swells them enough to create a seal and this is when they need replacement .
you can get away with just doing the upper intake orings but most people just do the she-bang ,uppers,lowers,ect,ect...

good luck .

^ What joe doe said, upper plenum has three pairs of o-rings that fail. May be a good time to change a leaky valve cover gasket and fuel rail gaskets while you're in there.