I have a 5.4L 2006 f250.

This vehicle has had a ton of problems and I bought it this way.

One of the last remaining problems is a stubburn P0171 code - lean bank 1.

I checked for air intake leaks by running a smoke test with a jerry rigged contraption powered by an air compressor. I also tried spraying carb cleaner around the intake manifold. I found no leaks.

There was an exhaust manifold crack and I patched that up with some steel glue. Not the best way of doing things but hopefully it will hold for a while. This improved the situation but I was still showing a lean condition.

My attention turned to the o2 sensors and I found some very weird behavior from them. I'm not an expert on o2 sensors although I've read as much as I can. Can any of you guys give me a second opinion on what's going on with the readings I'm getting?

I've made the following recording of my readings as I start the car. The video plays at triple speed to make viewing more convenient for you.


(It's pretty clear that the bank 2 catalytic converter is shot but that's no surprise since the computer was telling me the cat was bad anyway. Bank 1 is where the problem lies.)

 

Sounds like the O2 sensor is bad. They aren't that expensive and they do go bad. Sounds like you have a lot of miles on the truck for a cat to be shot. You need to fix the cat. WWWrockauto.com may be able to get the parts you need unless you need them today.

 

There's nothing there that indicates a bad O2 sensor.

You need to get the engine fully up to temperature before running those tests.

It also appears the PCM was very recently reset. You need to start out with a fully warmed engine, reset the PCM, then drive it normally until you get a pending or posted DTC, then look at the LTFTs for both banks. Both yours are still a zero. If you have a posted DTC, you also need to pull the freeze frame data.

Leave the possible converter issue till later.

 

make sure that exhaust exhaust manifold is good, that it's bolted tight to the head and the exhaust pipe, and that the crack is totally sealed. I would actually suggest getting another manifold from a junkyard that isn't cracked with a new exhaust gasket and putting that on and seeing what you get.

But it's also possible that the bad cat is partially plugged, and that can also cause the computer to get confused, as it reduces manifold vacuum.

Fix the two known problems [bad manifold and cat] and then see what's happening.

 

Yes, I reset the ecu by disconnecting the battery. I wanted to see the oxygen sensors' reaction to 0 fuel trim.

Before the long term fuel trim on bank 1 was 20% or 25%. I don't recall what bank 2 was.

What does freeze frame data show?

 

You need to know the trim for BOTH sides. A lot of times, it will code out on one side only, but the other is only a hair's breadth away from also faulting. In these cases, if you fail to also check the other side, you will incorrectly assume that only one bank has a problem when, in reality, both banks are faulty but only one had exceeded the limit. If only one bank exceeds the limit while the other is normal, you've isolated the issue to one side of the engine. If both banks are a-kilter, the problem is common to both sides.

The freeze frame data is a snapshot of a number of operating parameters that is stored when the fault code is set.

 

I already know the trim data for both sides. The second bank was a little high but nowhere near bank 1.

 

I've been thinking that I probably have misfiring because the engine idles rough and the roughness is erratic. However, I already fixed a prior misfire code by changing the computer and haven't gotten another misfire code since. Some people say that it's fairly common for this engine to have a misfire that's below the dtc trigger threshold and I need to read the Mode 6 data which I am having trouble doing.

 

What brand is that scanner you are using sir.

 

Hey everyone, I just wanted to update you all on what the issue was. As I already stated, I was not getting a misfire code after changing the computer so I thought I didn't have a misfire and my lean code was something wrong with the exhaust system.

However, since the car FELT like it had a misfire due to obvious engine roughness and vibrations, I thought I would check again by pulling the fuel injectors while running.

Guess what? There was another misfire. Even though that cylinder was misfiring ~90% of the time, it WAS NOT GENERATING A MISFIRE CODE. The OBD system on Ford is programmed stupid. Even a very obvious misfire was not triggering a code. The lesson here is to trust the physical symptoms and not the stupid obd computer on this ford.

Unfortunately, I do not have a fancy obd scanner. I just have a bluetooth one and it can read live data on some cars but not others. On a cadillac escalade (which isn't very new. maybe an 09?) I was able to read live cylinder misfire data but not on the ford. Even with Torque Pro and the Ford extended PID set, I got not data from this old vehicle. The Ford extended PID set in Torque Pro contains listings for live misfire data so I suspect that it does in fact work on newer model Fords.

The reason I missed the misfiring cylinder before was that it just so happens that I had swapped the bad spark plug from cylinder 1 into cylinder 3 to test the diagnose the spark plugs before. Cylinder 3 was throwing a misfire code from the beginning. It was just dumb bad luck that I happened to swap spark plugs from one bad cylinder into another. This obfuscated the problem with the spark plug from cylinder 1. Once I got it out and tested it with a multimeter, the cylinder 1 spark plug showed an open circuit so it was fried.

 

Someone has to be the brains of the operation, you's supposed to be you!

Do you know the difference between OBD1 and OBD2 emissions calibrations on a Super Duty? You need to.....

It works just fine on my 01.....