Lean code question?
 

ok Guys...i have a 04 Supercrew about 140k. I have been doing some work and have gotten really good results so far clearing a lot of codes! (P0022, P0345, P0174, on and on). The only code that still throws is P0171 Bank 2 too lean. My son had truck at College last 8 months!! I have checked over and over for vaccuum leaks to no avail. I read a post that says that code can come from poor fuel delivery also... So my question is this: if there is a problem with fuel delivery wouldn't ECM throw a code for both Banks? Or could there be a problem in the fuel rail on bank 2 only? Also, (I'm in Michigan) 1 cold morning i went out to start truck: she started right up.. Idled high for maybe 30 seconds but during these 30 seconds I heard 2 sounded like backfire coming from what sounded like catylytic converter on right side (Bank 1). If this is clogged can that confuse ECM into thinking opposite bank is running lean? And just because I live not far from Detroit and they steal Cats like crazy... what is the downfall of straight piping instead of replacing converter?? (Had mine stolen twice insurance replaced but with cheap parts I believe!!) I also seemed to smell gas when I heard the noise?

Lean codes can come from exhaust leaks too. Check your exhaust manifold on that side and the studs that hold them to the head. If the studs are broken then do a quick check of the trans mount on the cross member, a bad mount can let the motor shift and put pressure on the exhaust system and break the studs.

BTW what motor are we talking about here......they all have their own set of quirks.

Jgger, we're talking about the 5.4 3v... Did you break manifold bolts on drivers side? bank2?

Do not rely solely on the DTCs. You need to do in and look at the long term fuel trims for BOTH banks as that info will tell you the comparative shift in trims for both sides of the engine. It is not uncommon for one bank to code out while the other is just a small bit away from doing likewise indicating a issue common to both banks. It's relatively rare for one bank to be normal while the other is the only one with an issue.

Remember, "lean" codes do NOT mean the engine is running lean, it's the opposite! Those codes mean that the computer has reached the fuel enrichment limit but the downstream sensors are still indicating the mixture is too lean.

Most common causes, IN THIS ORDER:
Air entering the intake after the MAF sensor and is unaccounted for (vacuum leak) - oversupply of air.
Inadequate fueling, ie, low pressure, restriction, clogged filter, etc - under supply of fuel.
Exhaust leaks at allow fresh air to enter the system near the upstream O2 sensors.

Extended operation with a 'lean" code (or misfires) will too often ruin the converter due to the oversupply of fuel that hits the converter.

P0171 is lean bank 1, not bank 2. Bank 1 is passenger side.

No I haven't. I have a V-6 in my truck, so it is a different animal.

The trans mount and broken studs are something that the 5.4 can be subject to.

Follow the advise of Projectsho, he is a very smart guy on this stuff.