Need Help With Lean Codes Please! 2003 4.8 1500

[thearizonacowboy]

Trying to track down the cause of a couple lean codes on my 2003 4.8 Silverado 1500 (P0171 and P0174).

 

So far I've replaced the fuel pump, fuel filter, spark plugs, intake gasket, intake tube and all rubber, and the MAF.

 

Cold start it knocks like crazy and feels like its going to stall out. Once it warms up after 15-20 minutes on the highway it runs significantly better.

 

After unplugging the MAF it runs perfectly. Smooth idle at cold start and has plenty of power...

 

Any help would be appreciated!

[diyer2]

O2 sensor?

 

[thearizonacowboy]

Both banks showed lean at the same time so I doubt it but I probably should swap those out anyway... Thanks

 

[swathdiver]

Some logged data would be nice to see and help pinpoint your problem.  Know someone with a Tech2 or AutoCal or some advanced scan tool?

[Colossus]

How many miles?  Unless very low miles, your 02 sensors are certainly tired based on age alone.  it will help but may not be the overall cause of the issue. 

[thearizonacowboy]

8 hours ago, Colossus said:

How many miles?  Unless very low miles, your 02 sensors are certainly tired based on age alone.  it will help but may not be the overall cause of the issue. 

Oh not many, just 210,000 

[rjgti]

intake cracked

[sefiroxx]

Yes. check intake manifold.

Check water temp sensor(s). Failed sensor could be reporting to the computer that the car is warm and so additional fuel/air are not provided

Also, check ISC motor that sets idle speed. Falling motor or built-in tps could be cutting airflow.

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