Have been trying to diagnose a pesky P0172 Code (Bank 1 Rich) and it's getting the better of me. 2003 F150 SCREW 5.4L. Symptoms include horrible fuel economy, slightly rough idle. I assumed because only bank 1, not a MAF Sensor problem. Bad fuel economy prompted me to check injectors for a leak, pulled bank 1 fuel rail, key on engine off, no visible leaking. Started to look at O2 sensor bank 1 sensor 1, which seems to be a DIY'ers nightmare. Finally got ahold of a live data reader. O2 number seems reasonable but found a very low long term fuel trim value of -25%... then the kicker is that on Bank 2 where I do not have any code it's reading an even higher positive number of +29%. I can't believe I'm not getting the opposite lean code for bank 2 given that number. Any ideas?


Should add that about a year ago I had the engine pulled and had the common head repair done because of the flaw on rear of bank 1... had both sides done, timing kits replaced, plugs, etc. Recently had to replace pcv boot with major leak, and on bank 2 had a hole in one of the dpfe tubes so replaced those.

 

I'm a rookie at this, but what came to mind when reading your post was that maybe one cat is plugged up.

 

Look at all the parameters first for interpretation.
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Front Ox sensor 'action' both sides.
Rear OX sensor 'action' both sides.
Short term Trims both sides.
Long Term Trims both sides.
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Post them so we can see them.
Good luck.

 

From my experience if you have one long trim way positive and one way negative then you have a clogged cat converter on the rich side. I had one whoop my tail until I figured it out. And yes, bank 1 o2 sensor is a PITA to get to, the engineer should be tarred and feathered for putting it there.

 

Bluegrass7... the numbers were...


O2-B1S1 Ranged 0.035 - 0.795 at idle
O2-B1S2 Ranged 0.825 - 0.885 at idle


O2-B2S1 Ranged 0.065 - 0.765 at idle
O2-B2S2 Ranged 0.790 - 0.865 at idle


STFT Bank 1 Ranged -6.3 > +7.0 at idle (bounced neg. to pos. constantly)
LTFT Bank 1 Ranged Pinned at -25 throughout at idle


STFT Bank 2 Ranged -7.8 > 3.9 at idle (bounced around but large majority negative values)
LTFT Bank 2 Pinned at +28.1 throughout at idle


My reader records the data on a 60 count so I'm looking at 60 different readings for these numbers...

 

I've also had an unidentified rattle at times that sounds really bad, am a novice and didn't realize cat clog could make that noise. Might try the wooden stick to ear on the cats tonight... that rattle seems to pass when temp goes up. Don't think its the exhaust manifold...

 

Do you have any broken exhaust manifold studs?

 

From the data, it shows the front Ox sensors are acting normal in their swing range 'for an aged system'.
The rear monitor sensors are also normal showing small movements indicating the CATS are storing oxygen as they should.
This is not normally an indication of blocked Cats on either side.
However you can check this by doing a back pressure test if it comes to that.
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Since the code is set from bank 2 LTFT being out of limits (172) , either you have an air leak unique to just that bank being detected by the OX sensor or the program is stuck rich for some reason and hurting your fuel mileage.
Even consider an exhaust leak at the header, pipe or the EGR tube that is all after the motor but still detected by the OX sensor where it will falsely drive the fuel rich for that bank as a secondary but normal action..
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If it were me I would clear the memory so the possibility old history is not confusing the problem and see what comes back as new data, then begin looking for the cause.
You may see some changes in the live data but the original cause will still be there if it is not cleared by the program.
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I am taking you into more advanced thinking on this issue in trying to help the discovery process.
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Project replied before me and we both are thinking in the same direction.
Good luck.

 

great info. guys.. bluegrass the 0172 is bank 1 passenger side correct? is it fair to say that on that side of engine i need to check the exhaust manifold for broken or missing studs... check pcv tubing for vacuum leaks... and since bank 1 wouldnt that exclude the egr search? wondering if there is a novice way to check manifold for leaks other than just feeling to see if studs are all in place. To reset am i just disconnecting battery for a few minutes? thanks a lot for all of the help.. trying to wrap my head around the right way to figure this out without just throwing parts at it

 

172 is bank 1 set to it's lean limit.
The way the PCM has reacted to the condition can become confusing when trying second guess before the actual problem is found.
Sometimes it's a matter of what was detected first.
Check for exhaust leaks both sides from manifolds back to the sensors
The sensors are seeing air from some place to cause fuel tables to shift or excessive fuel in the exhaust.
EVAP system can even be responsible for the excess fuel.
Good luck

 

guys i was able to get my hands in there and confirm that all exhaust manifold studs are still in place and firm to the touch so i dont think any are broken. Had to replave stabilizer links so checked the best i could with tires off. I also dont see any problem at the junction of exhaust manifold with down stream piping just before upstream o2 sensors. is there a laymans way to cbeck for exhaust leak besides just confirming that the hardware is in place?

 

Let's review - the P0172 means the fuel trim is at the lean limit, meaning the trim is a negative percentage, meaning the O2 sensor has not seen any oxygen, meaning the PCM is taking away fuel on bank ONE (which is the passenger side bank). What would account for only bank 1 running too rich? Perhaps a leaking injector? Pull the bank 1 plugs and see if you can confirm.

Interestingly enough your data shows that bank 2 (driver's side bank) fuel trim is pinned positive, (but hasn't set the P0174 code yet), which means that bank 2 is near the rich limit (the PCM is adding fuel) to make up for too much oxygen content in the bank 2 exhaust. (The reason it hasn't tripped the P0174 code is that the PCM looks at the sum of the LTFT + STFT and sets the codes if the sum exceeds ~30%. IIRC, you said the bank 2 was running at +28% LTFT plus a negative ~5% STFT so its sum is around 23%.) So something that could make bank 2 run too lean without affecting bank 1 could be an exhaust leak upstream of the bank 2 oxygen sensor, or a leaking intake manifold on bank 2

You shouldn't have to look too closely at things like the MAF or the fuel pressure as those things would affect BOTH banks.

My novice way of looking for an exhaust leak is to have someone hold a rag against the tailpipe for a few seconds at a time with the engine idling while you look under the vehicle for any leaks. (Don't hold the rag too tightly for too long or you might set a code for the DPFE out of limits.)

 

Before you throw any parts at it loosen the exhaust at the passenger side manifold and see if the trims change. I had a clogged cat cause exactly the same trim values as you have. I couldn't figure it out and asked my shop foreman and he knew exactly what was wrong. He has been a ford tech since '85 and is the best diagnostic guy I have ever met.

 

Thanks a bunch guys for taking the time to respond. Still working on this and will be checking further for an exhaust leak and also will try loosening at bank 1 exhaust manifold to see if cat clog is possible. First look at those bolts tells me that they are going to break off almost without a doubt, so need to make sure I have replacements on hand.


Oddly, for some reason the idea of pulling the plugs has been looming over me and I've been putting it off. While I consider myself somewhat capable, I'm just a novice and that back plug worries me... just gonna have to bite the bullet and get in there to look.


My exhaust has been problematic in that I've had cat-back exhaust installed three times during the life of the truck. According to the exhaust guys, my short trip driving causes undo moisture and an excessive rusting problem. Right now both pipes from the muffler back are only "riding" in the muffler housing and are no longer weld attached. Should have mentioned that, sorry. Would love to just take care of it all right away, but having to keep budget in mind right now. Again appreciate all the time you've spent helping me out. I'll post an update asap.

 

Also going back towards the beginning regarding the fuel economy. Whatever this issue is the effect on fuel economy is absolutely incredible. I feel like I can literally see the needle sinking especially when below a quarter of a tank. Haven't yet tried to measure exactly how bad it is, but can tell you for sure that this thing is sucking down a ton of fuel. Thinking the fuel savings alone over about a month might justify any expense needed to solve this problem.