Bank 1 sensor 2 high voltage came up last week and went away, just had a CEL for Cylinder 5 misfire, does this point straight to a bad o2 sensor?

[Drawnnite]

So out of curiosity, a misfire from plugs/leads can lead to the o2 sensor after the cat having errant voltages, while pre cat one wont see it?
Wondering if it could be a "thing" with the L98 engine

 

[07GTS]

for closed loop operation the front 02's vary up/down controlled by ecu to hold stoich, the rears are not controlled so they just show where the front 02's are keeping fuel if all is good the rear 02's will be within the 350mv to 600mv range outside those its considered a fault rich or lean which id assume it would have to be there for a desired time before setting a code, any misfire will show as lean spike, if u reset the trims then if they were adding fuel and now they are not and have to learn all over again it would explain the code after the reset and then a day of driving they corrected and was better again

 

[krusing]

No sure if this is any benefit for the members,
But,
I had my Daughters car [Mazda 3] recently display the Engine Light come up
I scanned it, and displayed a Upstream O2 sensor DTC, P0134
So I purchase a S/H one and installed it, and the same fault appeared after I reset it,
I also purchased the Downstrean one, to be sure it wasn't the other one. [they were both from the same vehicle at the wreckers]

Low and behold, 1 day later my nephew rang and told me his MIL [2012 S2 V6 Thunder Ute] has come up on the dash,
So he come around, and bugger me dead, it was the same code,
Being Local, out of curiosity, I asked where he bought his petrol, and it was the same place [7eleven Black Rock]
So maybe there is some contaminated fuel out there ?
I ended up just used the fuel by running around in the Mazda 3, and resetting the Fault,
filled it up again from a different fuel outlet, [United Cheltenham], Has NOT Faulted once since
And my Nephew did the same, he filled up at another Fuel outlet [BP at Frankston] , and his has no fault since.

Hmm, coincidental or not ?

Site Note:
Dont worry, 7eleven was informed, and they were running checks the next day.
And did I hear back from them, Not directly tho, but through their insurance/claims contractor did asked me to get a quote to get the car fixed,
Which I did, I sent a request for a quote off the Brighton Mazda,
and NEVER Heard from them.

 

[jeffmills69]

Your ID Says your in Melbourne
What Area ?,
if you were close by, your welcome to call in and I would run the Autel over it.

As mentioned in an Earlier Thread,
I have always used a rule of thumb to set Plugs to 1mm,
as it makes the engines idle smoother,
and also less chance of the spark leaking/jumping to another lead, and/or to ground which could cause a misfire.

Cheers for that but you're probably 45km or so from my 5k radius and speaking of bad petrol it was suggested it could be an issue, I did after all start noticing issues around filling up at a random servo.. also generally avoid 7/11 as always seems to empty faster but thats a whole new kettle of fish

for closed loop operation the front 02's vary up/down controlled by ecu to hold stoich, the rears are not controlled so they just show where the front 02's are keeping fuel if all is good the rear 02's will be within the 350mv to 600mv range outside those its considered a fault rich or lean which id assume it would have to be there for a desired time before setting a code, any misfire will show as lean spike, if u reset the trims then if they were adding fuel and now they are not and have to learn all over again it would explain the code after the reset and then a day of driving they corrected and was better again

So the front sensors fluctuate and the post-cat stay at the same voltage or move slower?

And speaking of being better again, I had to go for a drive and noticed the acceleration was way more responsive so now I'm even more stumped, yet to scan it again though

 

[07GTS]

yes the rears are more steady but it dosnt take much to move them, all they do is once the fronts get lazy or out of range they will go outside there set range to trigger the code, or if they fail also trigger code, if fueling is kept at 14.68 by the fronts the rears should be showing around the 450mv during decel they may go close to zero or full throttle close to 1v

 

[jeffmills69]

yes the rears are more steady but it dosnt take much to move them, all they do is once the fronts get lazy or out of range they will go outside there set range to trigger the code, or if they fail also trigger code, if fueling is kept at 14.68 by the fronts the rears should be showing around the 450mv during decel they may go close to zero or full throttle close to 1v

Ah yep they were sitting around .800v in idle after a bit of a drive this morning and LTFT went from around -30% to -10% whilst driving which apparently points back to a vac leak.. time to pull some things apart and possibly tighten a few things I reckon

 

[07GTS]

-30 (or anything negative with trims) means its removing fuel so too rich, fuel trims show what they are adding or removing to get back to zero, its a complex thing as they have routines dependent on airflow so sometimes they may just be a little slower at idle or faster at higher airflow

 

[krusing]

Cheers for that but you're probably 45km or so from my 5k radius and speaking of bad petrol it was suggested it could be an issue, I did after all start noticing issues around filling up at a random servo.. also generally avoid 7/11 as always seems to empty faster but thats a whole new kettle of fish



So the front sensors fluctuate and the post-cat stay at the same voltage or move slower?

And speaking of being better again, I had to go for a drive and noticed the acceleration was way more responsive so now I'm even more stumped, yet to scan it again though

If it empties faster, maybe it has too much ethanol in it ?
Because E85 doesn't last the same k/m's as 91 or 95, nor does E10.
so it could be a fuel issue,
Where 7/11 fuel is provided by Mobil Petroleum,
but it could of been human error when they did the drop at the petrol station.