5.3L GMC low power

Tiny
ACFTMECH
  • MEMBER
  • 2003 GMC SIERRA
  • V8
  • 4WD
  • AUTOMATIC
  • 126,000 MILES
I have a 2003 GMC Sierra 5.3L with 126,000 miles. My problem began with sluggish performance, check engine light flashing when under a load and it was hard to start. I pulled the codes and found the P0300 Random Misfire code. I replaced the plugs/wires, fuel filter, air filter with no joy.
I checked the fuel pressure regulator and found fuel in the vacuum line. I replaced the regulator and the code dissapeared as did the starting problem. However; the engine still bogs down and will knock a little when under a load such as going up a steep hill, when I hit the passing gear, etc. I took it down the highway this morning and it struggled to get above 70mph.
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Sunday, June 12th, 2011 AT 4:53 PM

3 Replies

Tiny
RASMATAZ
  • MEMBER
http://www.2carpros.com/articles/engine-hesitates

Could be caused by one of the following below

Oxygen sensor.
Catalytic converter.
Fuel injectors dirty/sticking.
Mass airflow sensor/Airflow meter.
Throttle position sensor.
Crankshaft position sensor
Knock sensor
Manifold absolute pressure sensor.
EGR Valve
Fuel pressure regulator leaking or defective fuel pump.
Fuel contamination.
Foul/defective spark plugs.
Open spark plug wires.
Ignition coil/Coil packs defective.
Incorrect ignition timing.
Cap and rotor.

Note:If it doesn't apply disregard it and keep testing.
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Sunday, June 12th, 2011 AT 5:26 PM
Tiny
ACFTMECH
  • MEMBER
The truck is still starting ok but today the flashing CES light returned and finally went steady. I pulled the code and got the P0300 code again. It also pulled some freeze frame data as follows:

Fuel Sys 1 Open Loop
Fuel Sys 2 Open Loop
Calculated Load 39.2%
Engine Coolant 125deg F
STFT Bank 1 -10.9%
LTFT Bank 1 -2.3%
STFT Bank 2 14.8%
LTFT Bank 2 8.5%
Intake Manifold Press 23.9 inch hg
Engine RPM 3117 rpm
Speed 45mph
Mass Air Flow Sensor 12.69 lb/min
Throttle Position 42.3%

Does any of this info mean anything to anyone? I am curious why bank 1 is reading negative percentage and bank 2 is positive.
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Tuesday, June 14th, 2011 AT 2:02 AM
Tiny
RASMATAZ
  • MEMBER
P0300 Random misfire, check for vacuum leak and contaminated fuel-
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Tuesday, June 14th, 2011 AT 7:55 AM

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