Code P0136 - Oxygen Sensor?

[SmokinBarrel]

First, I'd like to say I am glad I found this site! As my truck is getting older, it helps to have back up when doing your own maintenance. I plan to keep my truck for awhile, so I want to keep it tuned up well. The engine is great, not a problem (knock on wood) for 145,000 miles. Ford F-150, 5.4L, 4X4, 2002 model, 145,000 miles. Anyway, I am now having issues with several things - here is the timeline: 1. On a 5 hour return trip from catching Skipjack in TN, my motor begins to cough, and flutter, in and out sort of speak. When I would give it gas, it would flutter worse. If I let up, not as bad, or not at all, and run fine on the highway. Or, it ran well at higher RPMs. 2. I get to St. Louis, and go by Auto Zone for a computer hook-up. The code is T0106 or something similar - not quite sure. "Cylinder 3" is what it said. I immediately think, it has to be a Coil. 3. I replace the Coil and not the spark plug, because I replaced the plugs at 100,000. 4. It seems to do well for a brief time, and the "Check Engine Light" doesn't go off. 5. I take it back up to Auto Zone, and this time the code states, "P0136" Oxygen Sensor, Bank 1, Censor 2. 6. So, I replace the Oxygen Sensor which is just before the catalytic converter, or directly after. 7. The "Check Engine Light" goes off. 8. But guess what, the problem or symptom hasn't gone away? I still have fluttering, when I press the gas, and the engine seems to go in and out of rough and smooth running. It does not do this during idle. Maybe a slight misfire during idle, almost like someone shuts off the gas for about .20 seconds, and then back on. I am planning to replace the spark plug in cylinder 3, just to make sure, and replace the coil. Then, I plan to spray the electrical connection on the Oxygen Sensor with electric auto cleaner to make sure it isn't shorting out somehow from dirt or grease. A pin or something maybe dirty. (of course removing the negative battery cable first) Could it be the MAF? I will admit, I have kept my air filter changed on a regular basis every 10 - 20,000 miles. Thank you in advance for guidance, I am at a loss! ** Update ** I replaced the spark plug, and the old one does look a little suspicious. Can you add photos to these threads? If so, I'll upload a photo of the sparkplug. It looks a little burnt around the base of the ceramic, where it meets the socket....dark brown/blackish ring around the base of the ceramic. Anyway, I replaced the spark plug, and coil, and cleaned the electrical connections. now I am waiting for 15 - 20 minutes before I hook up the negative battery cable.

[powersmoked]

I don't know what T0106 is. P0136 is an after cat o2 sensor. most after cat o2 sensors just read info but it does not affect engine mangement. it is good practice to clean the maf and iacv, I also would consider doing a fuel pressure test. how about fuel filter?

[SmokinBarrels]

Well, I replaced the sparkplug, and at first it seemed to be great. And thus far, it hasn't be as bad. Maybe a slight flutter, ever so often. Obviously, there must be something minor, like the MAF, or IACV.

I replaced the fuel filter at 80,000 miles. How often should you replace?

I will look those up in my manual and see if I can't get those cleaned.

Note: I should mention, I ran into this problem at around 90 - 110,000 miles. At that time, I was thinking Fuel Pressure, or fuel pump. I replaced the Relay (?) and FP regulator as it was a simple fix first. But, I don't think that solved the problem. I took the truck in and it was a coil. Anyway, at roughly 100 - 110,000 after this incident, I had several coils replaced at Ford, after I replaced all spark plugs. Basically, I screwed up the very back two - which are hard to get to, so I had to take it to Ford to fix. Anyway, after that, the truck ran fine!

So, some place inbetween 130 - 145,000 miles it began have this problem, fluttering one acceleration, oxygen sensor, and cylinder 3 codes.

Not sure if that additional info helps, but I am leaning away from fuel pump problems. I should probably check it. Is a FP kit inexpensive? And is it easy to hook up? I believe a Ford 2002 has a quick connect, for checking Fuel Pressure, correct?

[SmokinBarrels]

Update......

I replaced the spark plug and the truck is running great. UNTIL....I got on the highway and my "check engine light" came on again. This is after I reset the computer yesterday.

So up til now, it was running great, and still is. So, I stopped by AutoZone again for a reading, and again I got code P0136.

I am guessing it maybe a fuel pressure issue now? Although the truck responds well?

I also checked the MAF, and the small sensors look clean to me? Or, can that be deceiving?

[Bluegrass 7]

Here is some help for you.
First, the code 136 is being mis-interpeted. It is not the OX sensor but the cabling/connector or possible exhaust leak allowing excess air to enter ahead of the sensor.
Get that under control first.
Secondly, my feeling is you still have another bad coil causing the flutter under light loads that does not set a code, hence the confusion you are experiencing. Only ways to find the bad coil is a stress test or substitution one at a time and trial time to see if you got it cleared. The coil has shorted turns causing low volage output and is not a "hard" failure.
Take one issue at a time because their are two possible problems at the same time confusing you.
Good luck.