2003 ranger 3.0 flex fuel ...I am now getting code PO 172 after six months ok.......without the fuel trim data tool...that i may have to get...past year or so i have replaced camshaft sensor, plugs/wires/ 3 02 sensors.. air filter/fuel filter, intake manifold rubber gaskets, cleaned maf and tried used good maf.... cleaned throttle body, no vacuum leaks engine runs strong no miss fire....tried sea foam, fi cleaner all this in the past 12,000 miles...So this is what happens i get the code, clear it..then keep driving daily for about 100 miles all is ok, the code seems to come on when the a/c is on highway speed around 2,500 rpm as you know engine power will be pulled down with a/c on ...giving it more fuel seems to bring up the check engine light, i could be wrong.....question if there was a vacuum leak wouldn't the check engine light come on sooner ?.....now the engine has 158,000 miles..... PO did new heads 125,000 miles.... about a year ago i had the two codes 172 and 174 above repairs fixed it.......... at this point i am thinking about replacing the 02 sensor bank 1 again..... also i pulled the IAC wire.. rpm dropped to 500... PCV elbow ok no cracks

 

P0172 - lean on bank 1(passenger side) means computer is opening fuel injectors on that bank more that 15% more than it calculated , under 15% doesn't set the code

Engine is never actually running Lean, this code is only about computers calculations and O2 sensor feedback about Oxygen levels in the exhaust manifold

Computer is programed for engine size, 3 liters, so it knows how much air will be sucked in at any given RPM and throttle position.
It is also programmed with expected fuel pressure, 55psi in 2003
And it is programmed for the injector size, so it "knows" how much gasoline will be added to intake manifold if an injectors is open for say 100milliseconds.

MAF sensor fine tunes air weight for air temp and altitude, height above sea level.
Air:Fuel ratio is a WEIGHT ratio, 14.7 POUNDS of air to 1 POUND of gasoline, 14.7grams of air to 1 gram of gasoline

Upper intake vacuum leak or MAF sensor problem would effect BOTH banks

Exhaust manifolds run with negative pressure, they "scavenge" the exhaust flow, so when exhaust valve opens exhaust is pulled out leaving more power on the crank shaft since it didn't have to push as hard to get exhaust out.
It's what "headers" do, factory exhaust manifolds are "headers" they are tuned for mid-RPM power, lowest air pressure at mid-RPMs.
So if there is an exhaust manifold leak, even a small one, it will SUCK AIR IN at mid-RPMs.
O2 sensor "sees" this air/oxygen as Lean burn, false Lean.

So check for exhaust manifold leak

It is possible you got a bad O2 sensor, but I would just swap bank 1 and 2 O2s not replace bank 1, see if code changes to P0174

Could be lower intake manifold leak
Best way to find that is to REV engine then spray ether(quick start) along the edge of intake and head as RPMs go down.
When you REV an engine vacuum in intake drops low
When you close throttle plate the higher RPMs are still trying to pull in air, so vacuum in the intake get close to 30", at idle its 20", so better chance of sucking in ether thru a leak, it will make a pinging noise

 

Thanks Ron... no exhaust leaks, did the water test on manifold yesterday all ok.. I will try swapping 02 sensors... done 65 miles since clearing codes...all ok...just pulled 02s top one bank 1

 

P0172 is RICH on bank 1, my mistake

So computer is opening injectors for 15+% less time than it calculated

Do leaky injector test
After engine is warmed up..........
Have it off, turn on the key and press gas pedal down to the floor, all the way
Try to start engine, it should NOT start, it should not FIRE at all

Key on, engine at 0 RPMs, Gas pedal to the floor = Clear Flooded Engine Routine
Clear flooded engine shuts off fuel injectors but leaves spark on

As soon as you release gas pedal or if engine DOES fire computer will turn on injectors again.

Try the test to see if an injector might be leaking

 

Pedal to floor just cranked ..pedal off it started

 

Then no leaking injectors

 

I got a bottle of Lucas fuel injector cleaner today, give that a try hoping it's the injector spray pattern as I calnt find any vac leaks.. did pull the spark plugs bank 1 they were clean not black. will post results later... I did notice the exhaust tip is sooty, but wait this is a Cali ranger with 4 cats ??

 

Hoping this is my problem, seems to run smoother at idle, got three bottles, onto second one now, no check engine light so far, used the first one with 12 gall in tank,

 

So far so good, no check engine light...another 300 miles