O2 sensor bad?

[KenInCa]

Hello all, been lurking around this forum for years and just finally registered. (I know terrible )

There is so much great information that I really didn't need to ask questions, until now.

I have a 2003 4.6L XLT 2wd and initially I was getting good gas mileage, talking 5+ years ago, then slowly declined to 16, if I drive like a granny. Anyways been trying to get as much as I can, did the Gotts mod, have a K&N filter and I have a Edge Evo HT tuner. I was thinking about doing an exhaust until I guessed that doing just the muffler will not do much of anything to improve MPG unless I do a cat back exhaust.I tried all setting with less than desired outcomes. Could feel slight differences, but no improvements with mpg, actually slightly less. I finally tried the monitoring portion of the tuner and put the O2 sensors on voltage check. Side 1 (before cat, I'm assuming) was going haywire from 0.09v up to 6v or something like that. where as side 2 was much steadier changing as I increased speed. (I have a video of it on my phone if that might help) Also the trim (don't know what that is) for side 1 was going all over, where side 2 was at 99.21%, with no change from stop to 65 mph.

my question and hunch is that the O2 side 1 is bad, so why didn't it throw a code? Or is it side 2 that is bad?

If I were to change the O2 sensor, should I change both at the same time?

thanks for the help in advanced!

Cheers,
Ken

 

[KenInCa]

Update

well today I checked the O2 sensors again, adding the bank 1 & 2 side 1 & 2

Well, the bank one is still jumping all over the place for the front and back, where as the other side is changing slower, but not jumping from 0.1v up to 0.8v, then back down to 0.1v.

And its not throwing any codes.

HELP!!

 

[KenInCa]

Video

Here is the video link about how the voltage jumps all over the place:

https://www.youtube.com/watch?v=uvZm_EdgGbw

 

[FordandPolaris]

It might mean it is on its way out but not quite bad enough to throw a code. How many miles? Its a stretch but do you see the CEL come on when you first turn the key? If you do not then it could be not working for some reason.

 

[KenInCa]

It might mean it is on its way out but not quite bad enough to throw a code. How many miles? Its a stretch but do you see the CEL come on when you first turn the key? If you do not then it could be not working for some reason.

Just checked. The light comes on and goes off when starting the car.

It has 150K on it.

 

[toms89]

Bank 1 is passenger side.
Bank 2 is drivers side.

Then there is upstream and down stream. Upstream bank 1 & 2 is closest to motor and is what the pcm uses to maintain the proper the air fuel ratio. Downstream bank 1 & 2 is what the pcm uses to monitor catalytic converter efficiency.

The upsteam O2 sensors should toggle quickly between rich and lean. What your seeing is the pcm making adjustments (very rapidly) across stoich by adding or taking away pulsewidth from the fuel injectors. Stoich is the ideal air fuel ratio where you get the most complete burn. This about 14.64 to 1 with straight gasoline. The O2 sensors are narrow band so the pcm has no idea how rich or lean. By toggling back and forth across stoich is how the pcm maintains proper air fuel ratio in closed loop.

The rear O2 sensors bank 1 & 2 will not be toggling near the same rate because the cats alters the ratio or reading.

So you want an O2 that reacts quickly. As they age they can slow down or become non-reactive.

And if they are stuck one side or the other of stoich there is either a problem with the O2 sensor or engine. Vacuum leak, misfire, etc... in which the pcm cannot adjust for.

 

[toms89]

I believe the target voltage for stoich is .5 so look for it to go back and forth across .5 volts while in closed loop. (Upstream sensors)

I am not sure what readings are expected on the downstream sensors. Would expect it to be the same but much slower.

I can't read the labels on your video but the top right seems much lazier and slow to respond than the one on the top left. Going by that if I suspected a bad sensor I would say its the one on the right in your video. But it could just as easily be something engine related and the pcms ability to adapt.