DTC P0174-175 and P0300
Year: 2002 Chevrolet Avalanche 1500
Engine: 5.3L V8 SFI, Mileage 257771.
DTC: P0171-174- Bank 1 and 2 lean codes.
DTC: P0300B Random misfire
Checked for Engine data with scan tool
STFT B1 5.5%Idle 12.5% at 1500 rpm 9% at 2500 rpm
STFT B2 3.9% 6.2% 14%
LTFT B1 25%
LTFT B2 22%
MAF G/SEC 5.83 13.2 21.62
MAP 29.83 HG idle
Checked for intake air leaks found none, checked fuel pressure KOEO 35 PSI, specs 55-60 psi.
Removed and checked fuel filter was filled with dirt replaced fuel filter fuel pressure increased to 45 psi but not steady vehicle ran poor. We then replaced fuel pump with a new pump and we had 60 psi fuel pressure, the engine still was running poorly with DTC P0300 random multiple cylinder misfire. Checked coils seemed ok checked spark plugs were ok removed injectors cylinder 1 and 2 found filled with dirt and blocking the spray nozzle. As customer was in a tight spot for money we cleaned all injectors manually with cleaning spray solvent and installed the injectors. The car started and ran like new, it is best to replace the fuel filters every 50000 miles or check your owners manual.
Most cases it would be the intake manifold gasket or a bad intake manifold, besides both up stream oxygen sensors and mass air flow sensors need to be checked and eliminated.