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Oxygen Sensor Issue F250 6.8L v10


Bionicjoe

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I've got an O2 sensor that is throwing codes and causing misfires. P0171 and all the misfires are on odd numbered cylinders. Fuel trim just sets at 26.6% on the long term fuel trim. I cleared the data and drove around while watching the OBD data. Goes right to 26.6

Spark plugs were replaced 6 months ago and it ran perfect until I did some front end work and repaired a brake line. Had to remove the air intake. So maybe a wire got broken. There are no voltage numbers on this sensor.
Where do I find Bank 1-Sensor 2? All the videos I find just show the sensor on the exhaust.

Also I took it to the mechanic and they replaced an O2 sensor (my request) and verified there were no vacuum leaks.

2022-10-15 15_34_45-Window.png

15Oct22-3.png
 


RonD

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P0171 System too Lean (Bank 1)

On Fords with "V" engines
Bank 1 is passenger side
Bank 2 is drivers side

FYI, O2s don't cause misfires, you get Lean codes because of misfires

O2s only see Oxygen
When a cylinder misfires No Oxygen was burned up
That oxygen goes into the exhaust
O2 "sees" high Oxygen in exhaust because of misfire
Computer sets Lean code, and adds more fuel

For O2s "sensor 1" means upstream, closest to engine
"Sensor 2" means downstream, after cat converters

So on a "V" engine you will have two O2 sensor 1s, often abbreviated B1S1 and B2S1

If its a Dual Exhaust then it will have
B1S2 and B2S2, so two downstream O2s
Single exhaust just B1S2


O2s last 100k miles or 12 years, then they start to run out of chemicals to generate voltage, these are the ONLY sensors that do wear out on a regular schedule
O2s generate their own voltage, low voltage is Lean, high voltage is Rich, so...........................old O2s cost you $$$ in fuel


In any case misfire is not caused by O2
Could have a Vacuum leak in lower intake causing misfires just on that bank
Could be broken injector wire(s)

If O2s are older then by all means change them, that will take it off the table for you, but also makes the readings you are seeing more meaning full, because with old O2s you never know if the readings are correct
O2s have no "comparison" sensor, like all the other sensors, so computer relies on YOU to know if they are working like they should
 

Bionicjoe

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Thanks!
This issue came on all of the sudden after doing work elsewhere on the truck. So I would guess that it is a broken wire, and the sensor is not generating any voltage.

I think I need to find a better mechanic too.
 

Eddo Rogue

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Im always weary of o2 sensor issues, usually that means something else is the problem and the o2 sensor is fine, just dont like what its sniffin.

Can you switch o2 sensors or are they different? Can you test them? Or if you have the budget to parts throw new ones, get the good ones.
 

Bionicjoe

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Im always weary of o2 sensor issues, usually that means something else is the problem and the o2 sensor is fine, just dont like what its sniffin.

Can you switch o2 sensors or are they different? Can you test them? Or if you have the budget to parts throw new ones, get the good ones.
Well I've already got a new sensor installed. So I could switch them.
All I have to see which one got replaced. I think it was the one that is now showing 0 volts. So it wasn't the sensor, just a broken wire if that's the case.
I just don't have the time to troubleshoot it right now. Going to be a couple of days before I can sort it out.
 

Eddo Rogue

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Well I've already got a new sensor installed. So I could switch them.
All I have to see which one got replaced. I think it was the one that is now showing 0 volts. So it wasn't the sensor, just a broken wire if that's the case.
I just don't have the time to troubleshoot it right now. Going to be a couple of days before I can sort it out.
Heard that. I drive the beater till the next day off lol.
 

RonD

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B1S1 O2 is generating voltage according to chart
O2 voltage is under 1 volt
0.1v is high oxygen
0.9v is low oxygen

Chart shows B1S1 min. as 0.12 and max. as 0.45, so it is reading oxygen levels, just HIGH Oxygen levels, from the misfires

Sweet spot is 0.4, so upsteam O2s should have swing of 0.2v to 0.6v, and they jump around alot, that's normal

Downstream O2s should be steady as most of the Oxygen is burned up by Cat converters, so 0.75v to 0.85v

O2 sensors also can not work under 650degF, so exhaust must be fully warm up before "they" can be trusted, lol
Usually 4 to 5min of run time
They are Heated O2s so will usually work within 1 min of restart


Since the issue started after engine work I would start with the basics for misfires
Spark plug firing order
Since the invention of the multi-cylinder engines the firing order has been the bane of ALL mechanics, DIY or PRO

Show me a mechanic who says he never goofed up a firing order and I will show you a LIAR, LIAR pants on fire!!!, lol
Check it twice and then have a friend check it :)

After engine is warm and idling, and misfiring
Spray some fuel into the engine manually
If misfires are reduced or stop then you do have injector/fuel flow issues
BUT CHECK SPARK FIRST!!!
 
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Bionicjoe

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There was no engine work done.
Just front-end work and fixed a brake line right under the master cylinder. So I had to remove the air intake to fix that.
 

RonD

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Removing air intake reads like engine work?
Unless you just mean the air tube from air filter
 

Bionicjoe

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Removing air intake reads like engine work?
Unless you just mean the air tube from air filter
I just took out the air filter and bracket then folded back the tube.
Also unplugged a wiring harness that affects the air flow. Mass air flow sensor wiring maybe. Which is a good candidate for where a broken wire may now be. It's the wiring harness that runs out from under the master cylinder and over towards the engine.
 

Bionicjoe

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I think I found the issue. The shop replaced the wrong sensor! Not sure if the sensor is the issue or if it's in the harness further up. I still find it very curious how this all happened when nothing was done near the O2 sensors or exhaust.

To troubleshoot I unplugged the mass air flow and it died. Would start, but die immediately.
So MAF is good.

Unplugged the sensor on the pipe going up to the driver's side. This is the original sensor.
No change.

Unplugged the sensor closer to the Y but still on the passenger side pipe. This is the new sensor changed by the shop.
That sensor started acting like the other. So it is working when plugged in.

Both of these sensors are before the cat (or where mine should be had it not been stolen).
Maybe I'm still confused, but it seems like that other sensor is the issue. I'm going to change it. At over 300,000 miles what could it hurt?

Also found a slight exhaust leak. The previous owner was clearly a self-taught welder.
 

Bionicjoe

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Replaced the other O2 sensor. No change.
 

89Twincharge

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Honestly it's most likely a vacuum leak of some sort. You say you bent the intake pipe up so I'd check there first. If it looks good then get a can of brakkleen and while the engine is running spray the intake manifold where it bolts to the heads first then spray rest of intake. If engine stumbles or any thing check the intake bolts are tight as they sometimes back out on mod motors. Also if I remember right there's a pcv fitting on the valve cover that goes to intake check the rubbers on those. Lemme know what you find out...
 

Bionicjoe

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Honestly it's most likely a vacuum leak of some sort. You say you bent the intake pipe up so I'd check there first. If it looks good then get a can of brakkleen and while the engine is running spray the intake manifold where it bolts to the heads first then spray rest of intake. If engine stumbles or any thing check the intake bolts are tight as they sometimes back out on mod motors. Also if I remember right there's a pcv fitting on the valve cover that goes to intake check the rubbers on those. Lemme know what you find out...
Thanks but the sensor isn't showing a single bit of voltage or any type of readings. Even if there were a vacuum leak the sensor should register something. It's acting like the same as if unplugged
 

89Twincharge

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Thanks but the sensor isn't showing a single bit of voltage or any type of readings. Even if there were a vacuum leak the sensor should register something. It's acting like the same as if unplugged
B1s2 doesn't control fuel it is merely there to check condition of catalytic converter and will not cause misfires. Bending a fragile plastic tube on the other hand does create cracks especially in the flex areas. Since your cats were stolen b1s2 probraby had a cel since then... Your misfire didn't start then did it? Don't just chase the check engine light. It's merely an aid in finding some problems that are actually detectable by the ecu.
 

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