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Both O2 Sensors acting weird

Old 08-08-2018, 08:22 AM
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Default Both O2 Sensors acting weird

Friend just started having his truck running REALLY rough at idle and going through fuel like no other.
I hooked up HP tuners scan tool and saw that fuel trims are MAXED so I did some digging and here's what I found

-If I turn off closed loop with the scanner, it idles great and feels smooth as glass, just how it should be.
-All 8 injectors are firing. If I shut them off one by one I get a noticeable miss
-Both front o2 voltages are 1.1 V with key on engine off, then when I start the truck they plummet towards 0 pretty fast, and then stay at about .003v and don't move
-P1133 & P1153 are present
-Checked O2 fuse and it is fine

I have a hard time believing BOTH front o2 sensors took a **** at the same time, presumably for no reason. Other than just throwing money at it and trying to see if a pair of sensors do the tricks, can someone point me down the right path to effectively troubleshoot this issue?
Can anyone explain what would cause both sensors to show 0 v then add all of the fuel it possibly can with trims?
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Old 08-08-2018, 08:43 PM
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Did this just all of s sudden happin? Did he change the wiring harness or anything like tht. Ive seen the wrong o2 hooked on the wrong bank do things like tht. (As in pass o2 connected to bank1) One bank starts fighting the other bank vis versa, fuel trims max out trying to fix it.
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Old 08-09-2018, 01:57 AM
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Pull the sensors...hit em with a propane torch and what the voltage on a meter see if they swing or not. 0 volts = dead leann so the fuel trim will compensate for that so what youre seeing makes sense. Sounds like some dead o2 sensors to me.
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Old 08-09-2018, 07:29 AM
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Thanks for the responses, here's a little update to the story.
Just for diagnosis, we swapped out the rear o2 sensor with the front (they had the same denso number on them, just different length pigtails) and everything started reading just fine up front but now the rear was reading messed up.
Problem followed the sensors.
So, 4 new sensors are on order (replacing fronts and rears to not have to deal with it again) all denso brand. Will report back to let you guys know if it fixed it.

I've never seen both front sensors go bad at exactly the same time...all I can think is one went bad and only trimmed on one bank, so it wasn't noticeable enough to run super rough, then once the other sensor crapped out, it finally ran rough enough to start diagnosis.
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Old 08-09-2018, 11:13 AM
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Read on other threads that things like Antifreeze or other chemicals can kill your O2 sensors, maybe something hit the fronts like some cleaner or additive or something that didn't make it through the CAT to the backs? Just a thought, it is strange that both went out.
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