I have a 2001 ford ranger 4x4 edge 4.0 v6 with 157,000 miles. i have been getting very poor gas mileage around 12 city. i cleaned EKG valve, MAF sensor, new spark plugs and wires, fuel injector cleaners and nothing has yet to work. i do not have a check engine light or anything and the truck runs very smooth and clean out the back. i decided to buy a OBD2 scanner to check the live feed data. short term fuel trim and long term fuel trim hover around -.1mv . O2 bank 1 sensor 1 fluctuates normal from .1-.750mv, O2 bank 1 sensor 2 stays at .725 and DOES NOT FLUCTUATE, O2 bank 2 sensor 3 fluctuates normal from .1-.750mv. Could this cause a bad fuel consumption? please help and give feedback
thanks- james

 

Welcome to theforum

There are only two O2 sensors that you need to look at on V6 or V8 engines
Bank 1 sensor 1 (passenger side upstream/front)
Bank 2 sensor 1 (drivers side upstream/front)

Bank 1 sensor 2 is after the Catalytic converters, it is there to test if they are working.
Bank 2 sensor 2 would only be found on Dual Exhaust vehicles,because they have 2 sets of Catalytic converters

Not sure where you got "sensor 3"

B1S1
B2S1
Those are the two signals that tell the computer if engine exhaust is Lean or Rich, and these are called Upstream O2s

O2 sensors generate their own voltage, by a chemical reaction, but this chemical reaction can't happen under 600degF, so O2 sensors are not used for a few minutes after starting the engine, they need to get HOT!!
When they are hot they generate a voltage between .1 and .9 volt, so under 1 volt
.1v is Lean
.9v is Rich

Sweet average is about .4
But volts should jump quickly up and down between .3 and .6, the reason .6-rich, is to keep Catalytic converters working, they need a little unburned gasoline to stay "running" hot

So fast switching voltage is GOOD, slow or no switch can be bad O2 sensor, OR that bank is running TOO Rich(.9) or TOO Lean(.1), and computer can't correct it

STFT(short term fuel trim) is the result of the computers calculated air/fuel mix and the data from the O2 after air/fuel was burned in the cylinders on that bank
+1% STFT means computer saw Lean "average" voltage from O2, so it is adding 1% more fuel than it calculated
-1% STFT means computer saw Rich "average" voltage from O2, adding 1% less fuel than it calculated

-5 to +5 STFT is normal, and it will pop up to +10 or so at idle and accelerating, need a Richer mix at idle and of course for a bit more power.

-15 or +15 is when computer will start to set codes.

You need to get your STFT reading, live voltage, unless it is in graph form, is not helpful




If your MPG has dropped then check the Damper on the Fuel Rail, should be passenger side by firewall, it has a vacuum hose attached, if Dampers diaphragm starts to leak raw fuel is sucked in to engine sending MPG down, check that vacuum hose for gasoline

Sensor 2 shouldn't change fast, it sees a steady flow of "clean air" after the Cat converters, and .7 is normal

False Lean can cause poor MPG, if you have a loose O2 sensor or an exhaust manifold leak, these SUCK IN AIR, and an O2 "sees" oxygen in the exhaust, thats what it measures
So an air leak around O2 sensor or exhaust manifold causes False Lean, O2 sees too much oxygen so computer runs that bank Richer than it should, no code, just poor MPG

leaky muffler or pipes don't do that, air leak must be between engine and upstream O2

 

typo- o2b1s2 stays at .700 and o2b1s1 and o2b2s1 are normal. and yes i drove the car around for about 10 mins to heat everything up then checked the o2 voltage. also my STFT and LTFT are -1. what could be the problem then?
thanks for the information very helpful.
-james

 

Neighbor kid with siphon hose?
LOL

-1 is normal, no clue as to a problem there

Check your coolant temp on the OBD reader, should be 185degF or higher after warm up
under that means lower MPG
Thermostat should be 190-195degF

How are you calculating MPG?
Tires size must be factory or Odometer will be off, it will be lower than actual miles traveled so lower MPG than it really is.

Check filler hose on gas tank, any cracks or holes will allow gasoline to slosh out which for sure will lower MPG

 

i have patagonia a/t 265,35,16s on my truck which is the stock size tire. and i measure mpg at the pump, every time i get gas i fill it up till i cant put anymore gas in and then put the odometer on then go back to pump and fill up all the way and i divide how many miles i went on the trip by gallons of gas i pumped. I will check the hose on the gas tank, and coolant temp tmw. thanks for the feedback!
-james