Fuel Trims

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SJP

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I recently experienced high lean fuel banks 1 & 2 in my 2003 chevy 4.8. Than my fuel pump went out. So I was thinking that the lean fuel readings was coming from low fuel pump pressure caused by a weak fuel pump. After replacing the fuel pump my truck threw the P0171 & 0174 codes again. I have checked almost everything that could cause those codes, in addition to replacing the fuel pump I replaced the fuel filter, spark plugs, checked for intake and vacuum hose leaks. And every thing checked out ok. So I went back wards and got to the fuel pressure check again and it was 50 psi. I found through the Chilton repair manual that the fuel pressure should be 55-60 psi for my truck. The fuel pump that I brought was a Airtech aftermarket brand. It would have taken 3-4 days to get the AC Delco and I needed to get the part in the same day. So could the lack of 5 psi cause a lean fuel condition?
 
Have checked all of the above except the exhaust system for leaks. and have come full circle back to the lack of fuel. Before I start pulling fuel injectors I want to investigate the lack of 5 psi that is below the manufactures specification for my truck and will that amount of loss pressure cause a lean condition.
 
thats an awfully close the spec reading, how did you determine you dont have a faulty O2 sensor? As the link suggested did you use an advanced scan tool?
 
My scan tool is not the most advance but it do have a mode that test the oxygen sensors and a function that test the status of the emission system readiness and the drive cycle verication and the O2 sensors always checks out ok. I was under the assumption that meant the the O2 sensors is operating properly, am I under the wrong assumption? Not throwing any codes for the O2 sensors but with the readiness check and the absent of DTC codes for O2's can the still be the culprit or the lean condition? By the way I brought the scan tool from Harbor Freight, it' the deluxe model... not the greatest equipment but it is functional.
 
Well since it's a brand new pump you would expect it to output the minimum so I would go for another new pump.
 
I'll go to Auto Zone and see will they let me pay the difference for the AC Delco fuel pump, and I am also going to change out the O2 sensors any way. Thanks
 
Finally confirmed Intake Manifold leak, it is so small it took a smoke test to find it. Had to read the fluctuation of the LTFT to confirm the leak. Do anyone have have a repair diagram for the intake manifold gasket on a 2003 Silverado 4.8?
 
Update: Found that the intake manifold had a small leak. Only way I found it was a the homemade smoke test, i.e blowing cigar smoke into the brake booster vac hose. Replaced the intake gasket, was not difficult but time consuming about 5 hours because of first time, 3 hours next time. After replacing intake gasket my rear main seal that has had a very small leak for about 3 years seemed to just burst open leaving a puddle of oil each drive cycle. Considered taking to shop but thought I would try this additive called Blue Devil Rear Main Sealant, they claim that it forms a permanent seal, Well after 2 days of driving I have not seen one drop of oil. They also claim that the product don't have to be reapplied when oil is changed. I change the oil this Saturday to find out. Have anyone heard of this product. Brought it at Advance Auto for $11.95 on sale regular price $18.00
 
You are sure the leak was from the main and not from the back of the intake manifold. Glad the product worked for you.
 
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