Hi I have an 98 ranger 4.0 @245k KM (149k miles)and I’m trying to find out why my 4.0 is having poor fuel consumption. I’m currently only getting around 400 km (248 miles)per tank when I should be doing around 530km(320 miles)per tank at the low end.

I've changed spark plugs, spark plugs wires , washed the MAF sensor, new filter, clean intake and throttle body, oil changes every 8000k.

ive recently checked my O2 sensor and it’s giving me wierd readings, if anyone know if this is normal the data comes from up stream 1 and 2 sensor. If anyone needs more data feel free to ask I will provide them.

 

Welcome to the forum

First, O2 sensors are THE ONLY sensors that wear out, 12 years or 100k miles that will start to run out of the chemicals they need to detect Oxygen in the exhaust
So if you don't know the age of the 3 O2 sensor, replace them, graphs are meaningless unless you know the O2s are less than 10 years old

O2 sensors make their own voltage, 0.1v to 0.9v
As they start to run out of chemicals the voltage goes down, that means "lean" to the computer, a false lean, so MPG slowly starts to go down, imperceptible over a few years but its costing you money, and at todays gas prices, you could by 10 O2 sensor before you would notice it


There are 3 O2s on a 1998 V6
B1S1 is passenger side near exhaust manifold,
B2S1 is drivers side near exhaust manifold
these should switch voltages very fast, average should be 0.45, slow or no switch is a failed O2

B1S2 is after Cat Converters, this one is switches slower and should average 0.75v to 0.85v, lower means Cats are bad or O2 sensor is too old, I would change the O2 sensor first, lol

All the O2 are the same models, just different length wires attached
Bosch are what Ford used