High fuel consumption, O2 or some other issue

[tmarat]

Happy new year everybody!

I have an issue with high fuel consumption. Currently it is winter time with temperatures about -10C to -16C/14F to 3F, and I am seeing about 28l/100km, 8 - 8.5mpg. I don't do a lot of idling for engine warming, but the trips are usually short, 7-8km, or about 5miles.
I see that bank two always has high ltft (long term fuel trims) 5-10, while bank one is usually 3-5. Ignition coil had a little crack just below where the ground connector (goes under the bolt), so I suspected maybe a spark issue, as insufficient fuel burn will also lead to positive ltft. Replaced ignition coil (motorcraft), spark plugs (denso iridium) and the spark wires (motorcraft). But this did not change anything, in fact right after replacement I had rough idle, which went away after some time (mostly, still some roughness from time to time, KAM reset through battery disconnect for about 15mins).
The O2 sensor for bank two seems to mostly show rich condition (0.7v), and does not fluctuate much. At idle it is pretty much at 0.7 and starts moving a bit only while driving, while the bank one sensors do move up and down. What I don't get is why then the ltft is still high? As the o2 is reading rich, shouldn't I be seeing negative fuel trim? At engine start I do hear pops from time to time suggesting some fuel is being burnt off in the exhaust. They are gone after warm up, but quick rev ups while stationary still lead to those pops again.
Tried testing the o2 sensor by disconnecting a vacum hose to see the reaction, below is a video. Is this o2 sensor functional or dead?

 

[Flag Gibby]

I cannot tell what you are plotting in most of your video, however it does look like your fuel trims are responding to the vacuum leak. I would be plotting the O2 voltage as you introduce a vacuum leak. How many miles on your fuel filter? Also see here for individuals with a similar issue and steps to take to help track it down. For testing an O2 sensor: http://www.explorerforum.com/forums/showpost.php?p=3491873&postcount=5 Issue with a V8 but much of the troubleshooting information is applicable to the V6: http://www.explorerforum.com/forums/showthread.php?t=437676

 

[tmarat]

Four graphs on the first screen are the o2 sensor voltages, bank1 (top, ups/downs) and bank2 (bottom). Below them are the rpm and speed. Next screen to the right is for short term fuel trims (bank1 and bank2), and the next screen is the ltfts, again bank1 and bank2.
I had initially confused the o2 upstr/downstr. O2 seem to be fine.

Though the link given in the post that you referred to states low voltage means rich and high voltage means lean condition, while what I have been reading was the opposite, they contradict each other.
http://www.fourwheeler.com/how-to/engine/1403-driveway-diagnostics-bad-oxygen-sensor/
Readings below 0.3-volt tells the computer the mixture is rich, while readings above 0.6-volt tells the computer the mixture is lean.

http://www.autodiagnosticsandpublishing.com/feature/o2-sensor-testing.html
if the oxygen content is low it produces a high voltage (0.90 Volts - Rich mixture) and if the oxygen content is high it produces a low voltage (0.10 Volts - Lean mixture). Although theoretically the O2 sensor should cycle between 0.00 volts and 1.00 volts, in reality it cycles between 0.10 volts and 0.90 volts.