PO174 being only bank 2 cannot be fuel pump or MAF - Right?

[MH_Stevens]

At 250k on my 2003 Land Cruiser (plugs and coils all new OEM) I have the common PO174 code, "lean bank2". I have been told that it's likely a fuel pump or MAF issue but surely a problem with these items would affect both sides? Any thoughts where to start diagnosis?

 

[excessive]

maybe start with a fuel filter xchange ? cheap and easy

 

[OEMGUY0720]

It’s possible. Lean/rich errors can be attributed to fuel pump, MAF, vacuum/intake lines leak and upstream/downstream oxygen sensors.

 

[2001LC]

"Typically" only one bank fuel lean DTC (code), is not MAF. It usually something that only effects that bank. This can be to much air or to little fuel in mixture. Or so ECM thinks so, primarily, by data from BK2 O2.

I would: Watch fuel trims, while MPH & RPM steady on flat HWY. If only BK2 LTFT lean. Yet BK1 normal ~0 to ~5%. Then, this is a BK 2 issue. When only one bank lean, look for issue that only effect that bank, first.

Look for vacuum leak at intake manifold gasket leak BK2. Was intake manifold removed for any reason!

You may also have fuel injectors (FI) BK2 clogs. 2 cans 44k or other top shelf fuel system cleans, then CatOclean (paint thinners plus). May help.

Inspect BK2 O2 and or exhaust leak.

If both BK's running lean. Do all the same for both banks. Giving a little more focus to fuel pressure/flow and MAF.


Compression test is also, on the table. But I'd be looking else where first.

 

[MH_Stevens]

Thanks, this is great response.
As they are 2003 originals I think I may first put in new o2 sensors. Which ones are most likely to be bad, however the live data does not indicate a problem. I'll run the cleaner. IF IT HELPS around town I'm only getting 5mpg!

 

[2001LC]

Thanks, this is great response.
As they are 2003 originals I think I may first put in new o2 sensors. Which ones are most likely to be bad, however the live data does not indicate a problem. I'll run the cleaner. IF IT HELPS around town I'm only getting 5mpg!

WOW, 5MPG is bad. Which suggest a condition where excessive fuel is being added by ECM.

May be best you stop driving, or limite to only short distances not going much over ~2,000 RPM. If to much raw fuel is getting into CAT. Higher RPM heat CAT more. You could them burn up. You're could also by washing cylinder walls with so much fuel.

The BK2 lean, with 5 MPGH with P0174. Suggest, the system is trying to compensate, by adding fuel. Which result in poor MPG. "Compensate" meaning, your dumping excessive fuel into combustion camber (cylinders). Working hard to correct, excessive O2 in combustion camber. But ECM can't get enough fuel into BK2, to compensate for so much extra air. Which 8 out of 10 times is due to vacuum leak. You could have more than one leak and more than one issue.

So first thing. Check for vacuum leaks and correct. Driving with this much fuel use, could burn-up the CATS and or damage cylinders.

I'd make sure, good air filter.

I'd very likely go ahead and replace MAF (OEM only). Make sure to disconnect battery negative cable, before R&R MAF. Reconnect after battery, after a minimum of 20 minutes has past. I'm finding minor improvements in fuel trims & MPG, replace these old (MAF) even when they test okay. These are very sensitive sensors.

After 3 drives, of bring engine to operating temp and allowing to cool down in-between drives. Log fuel trims again, while RPM & MPH steady with out any change to throttle (gas pedal). If they stay in the 5% range. Go for higher speeds/RPM. Shorter runs at first, to help clear CATS. If Fuel trims looking good. Work up to high RPM runs on HWY, to cook off o2's and CAT.

You mentioned new OEM coils & spark plugs. If not purchase from Dealership or very trusted wholesale of Denso parts. I'd also give them a hard look.

O2 can be funky and not give a DTC if, just out a bit from spec range. But they'd "likely" only be minor contributing factor. They may also be in range, but getting gunky from excessive fuel.