Hi, I've added keywords below in hopes this might help someone else.
2003 285K F-150 5.4L 2V Crew Lariat, Last week replaced intake manifold, cleaned injectors, new plugs, new exhaust manifolds (hard torch time on bank 2), new AC system. Truck running way rough at idle. 1st timer with code reader, P0131, when I saw is was a pre-cat O2 sensor and I had a "small fire" when torching bank2 exhaust manifold, I ASSUMED the code was for bank 2. Sure enough, the Bank 2 pre-cat OS sensor harness was burnt. In great confidence I set out to rewire and search howto...

Then I learned... PO131 is for Bank 1, sensor 1. sigh.... But visually my trusty heat shield had failed and I had clearly toasted HO2S 21 or 2/1. To verify the live data reading showed 0.0000 for B2S1, so I cut the sensor wires in prep of rewiring.

With 7 kids, just out of, in, or going to college this is my current job vehicle, so... I'll run a new wiring harness for the Bank2 Sensor 1...

To the question.. Why O Why... does my Cen-tech code reader show P0131 (bank 1, sensor 1) when clearly (bank 2, sensor 1) is toast (literally) and am I barking up the wrong tree (super rough idle after intake replacement).

Thanks so much... hoping someone can help me get my only income ride going.

Keywords: 2003 5.4L intake exhaust manifold intake Oxygen sensors HO2S Bank 1 Bank 2 PCM Engine Controls, O2S11 O2S21 rough idle

10/21 6:30am update. Thank you so much for helping and education on sensors... I fear all this work is going to come down to... I should not of cleaned/reused the injectors. Onward...

I was able to rewire the bank 2, sensor1 wiring harness and did confirm the are both working. I also recreated my smoker, and the only leak I could find was the large spring clip on the air filter which I taped /sealed.

No improvement. Attaching idle and 2500rpm live data. 1st batch is at 2200-2500rpm.










And then the idle live data.

 

Do not assume that you have an O2 issue, use a proper SCAN tool (computer), and read the live data, MAF, O2, and fuel trim.
I would start looking for a vac leak, to begin with.

Did you burn a hole in the manifold or is it sealed correctly?
If there is a leak there it will change the o2 readings as the PCM reading is now going to add fuel for too much air.

By chance did you let the truck run long enough to get out of the closed-loop?

To verify the live data reading showed 0.0000 for B2S1: It can and will read this in a closed loop. The downstream oxygen sensor (sensor 2 on both sides) should produce a steady voltage of approximately 0.45 volts, but in a closed-loop, they may not.

Do you know how to test an o2 sensor with a multimeter?
It will take two people for that test and I think this test will show you better below.

What did the others read?

Here is a quick test you can do on the o2 system. (Don't worry about the downstream ones reading yet)Now, take a look at the voltage readings for O2S11 and O2S21 before doing this. (Look at them and write down the numbers)
If the engine has been running for about 20 minutes or more, with the temp of water up to normal there about and the 02 sensors are OK, you should see the voltages moving between 0.200 Volts and 0.900 Volts.
If the Voltages are not moving between 0.100 and 0.900 Volts, don't worry about it just yet, continue on to the next step.
You're not going to be able to spray carb cleaner into the throttle as the engine is running, because if you were to do this, the engine will die as soon as you disconnect the air duct from it (to spray into it).
With the engine running, spray a little carburetor cleaner into a vacuum hose (that has an engine vacuum like the brake booster vac line which works best) while you observe your scan tool's display screen.
If you spray too much, the engine will stall. If this happens to you, just restart the engine and repeat the step and spray less carb cleaner.
As you spray some short burst of carb cleaner into the vacuum hose, you should see the voltage numbers of O2S11 and O2S21 immediately spike to 0.800 to 0.900 Volts. And as long as you're spraying, these voltage numbers should stay there.
When you stop spraying, the O2 sensor's values should come down and within a few seconds, they should start oscillating between 0.100 Volts to 0.900 Volts. If they don't, don't worry about it yet.
O2S11 and O2S21 voltage numbers spiked to 0.900 Volts when you sprayed carb spray into the vacuum hose. This tells you that both oxygen sensors are OK at this point in time. They do not need to be replaced, since what is causing the PCM to think they are fried is something else.
O2S11 voltage numbers DID NOT spike to 0.900 Volts when you sprayed carb spray into the vacuum hose. This confirms that Bank 1 Oxygen Sensor 1 is no longer working. You can replace the oxygen sensor.
O2S21 voltage numbers DID NOT spike to 0.900 Volts when you sprayed carb spray into the vacuum hose. This confirms that Bank 2 Oxygen Sensor 1 is no longer working. You can replace the oxygen sensor.
The downstream o2:
The purpose of the downstream, after converter, sensors is to monitor the quantities of harmful exhaust gases flowing into and out of the catalytic converter to ensure the converter is working properly. See above for their readings of .045

Try this and see what happens.

 

Just some thoughts after reading your input:
Be sure you know bank 1 is the passenger side.
There is likely a vacuum leak in the intake system at some point you are missing.
Even if the Ox sensors are disconnected, the motor will still run pretty well as long as there are no other faults.
Reason is the PCM substitutes a fixed value in place of the Ox sensors to keep the motor running and not be a disabling fault.
Result is the motor is fed a bit rich on fuel for protection.
If this is combined with an intake vacuum leak you will have what the results you now have.
Over richness or leanness.
A note; the first cat is not a pre cat. It is the first and main cleaning of the exhaust. It has to light up to 600 to700 degrees to work, so nothing Pre about it.
Good luck.

 

Bluegrass, thank you. Pls remember I've never delved into any of this... but this is what I've learned from your and stonedpony's input.

I fixed the HO2S21 harness and all is now well with the measurements, trunk running worse than evern. So far I've found the Dorman replacement intake manifold is NOT a robust sealing product (guessing flexing). Turns out the delta between shrtft1 / longft1 was and shrtft2 and longft2 were way out of spec. A very close inspection of the new intake seal found coolant spiting out of the head bolt area, so I retorqued at 21 Flbs (18 is spec), the live measurements and delta are drastically better, might even be in the 15% spec delta.

Truck still running like ... terrible, classic dead cylinders, for example I can pull the wires from Cyl2's COP and there is NO Change... so, I'm going to back up and retest the coil packs and go from there.

Did I mention this truck ran like a sewing machine with 283K miles.. sigh.

 

Your long term fuel table 1 shift is the problem.
A vacuum, leak. Dorman and gaskets is usually the cause. Seen it before.
The motor is running way too rich on bank 1. You should see a code 171 from it (if ) the Ox sensor for that bank is working properly because it detects excessive oxygen in the exhaust for that bank. and richens the fuel, [that becomes the problem].
Fix that first, then any other issues.
Good

 

Bluegrass, I think you hit the nail on the head along with stonedpony. Once upon a time I was an SW/HDW engineer and all of your feedback forced me into study mode again. As you can see, the O2B1S1 and OSB1S2 are very different, which is driving the ECU to obscenely crank the fuel trim in bank1, which STRONGLY suggests I have a Bank1 vacuum leak, likely the NEW dorman intake... sigh again....

Oh I did old school, as my scanner really didn't help with confirming no miss-fires. So purchased a $12 engine stethoscope, using it I was able to confirm ALL my injectors were happily firing, I think I could even here my coil-overs clicking happily away.

So, with sensor B2S1 harness fixed, all coilovers and injectors happy, and with help from all, it's clear as mud that Bank1 is being hammered by a intake leak... sigh....

Btw, this plug near the windshield wiper tank, Red/Yellow and Violet... its been nagging me as I can't find a home for it... anyone?

thanks again... now to remove freaking everything and start over...

mystery plug on windshield wiper tank harness, red/yellow and Violet? Purple?

 

Your mystery plug is for the high pressure a/c switch.

 

I don't have one! Does it screw into the schrader valve which then this plugs into? I must of tossed it when to threw out the old AC lines... sigh....