2006 LL8 - P0171 - Lean LTFT (+12-20%) - Intermittent MIL

[griffincox]

Looking for some help with an ongoing and unresolved issue. This started 6-9 months ago and has been the same issue and symptoms since.

Issues/symptoms:
Intermittent MIL - will come on/go off every 3-6 run cycles.
P0171 - Lean bank 1
No other powertrain codes
LTFT is consistently +12-20% (adding fuel)
Occasional minor startup and idle stumble. Very minor. No other drivability issues. Will run full load, full RPM without hesitation

I have smoke tested the intake system twice. No sign of leaks. Cleaned throttle body. Replaced intake manifold gaskets. Replaced PCV hoses. Replaced fuel tank cap. Both O2 sensors and all spark plugs have been replaced recently.

Current thoughts:
Low fuel pressure?
Exhaust side air leak?

I am out of ideas about what is causing this lean condition.

Thank you!

 

[TollKeeper]

What spark plugs did you use?
What O2 sensors did you use?

Only other suggestion I have really is to pressure test the before and after cat. I know there is a video about it on South Main Auto on YouTube.

 

[griffincox]

What spark plugs did you use?
What O2 sensors did you use?

Only other suggestion I have really is to pressure test the before and after cat. I know there is a video about it on South Main Auto on YouTube.

OE and OE.

Thanks for your help!

I will start looking at the exhaust system.

One thing I failed to mention is that I also suspect that the Secondary Air system. I took the hose off the valve at the manifold and plugged it. Lean condition persisted. Any further testing warranted there?

 

[budwich]

Check the MAP... original? ( replace... its relatively cheap).

 

[griffincox]

Check the MAP... original? ( replace... its relatively cheap).

MAP data seems correct. It is original. I have another known good I can swap in. Are these known to go bad?

 

[TollKeeper]

I can't help with the secondary air system. I know nothing about them

 

[mrrsm]

This video concerning Diagnosing the Cause and Origin of the P0171 Issues is very useful, interesting... and edifying:

 

[Mooseman]

Even with the hose plugged, the SAIS can still cause issues. Only way to completely eliminate it is to block it off on the head. That could be done by inserting a piece of sheetmetal and another gasket between the valve and the head or using a block off plate from an 02-03. If that is the cause, you can leave it off and have your PCM tuned to turn off the codes for it.

You should also try finding a vacuum leak using carb cleaner as sometimes just smoke doesn't have enough pressure to push through a marginal seal or hose.

I would also check the fuel pressure and see if the pressure regulator holds the pressure when you shut it off. You can rent the gauge kit for free from most auto parts stores.

 

[rchalmers3]

I'm a few months behind you fellas on a response, but I had the thought that an air leak at the brake booster may be a source of false air entering the manifold.

Easy enough to test by pinching the booster hose while monitoring the LTFT counts.

Rick

 

[rchalmers3]

Sorry for another "late to the party" contribution, but in my former life as an automotive technician, we utilized propane to administer unmeasured fuel to the engine in order to monitor the computer response to the additional fuel. The propane bottle was fitted with a normal torch, and placed (unlit!) in the intake air-stream, usually where the air filter resided.

Rick