2005 gmc sierra 1500 5.3 check engine light flashes code po300 tuned up, repaced O2 sensors and catalack converters also checked for intake leaks and fuel pressure still flashes with a misfire multiple

SOURCE: 1997 gmc sierra 1500 5.7 vortec got spark got fuel

You said you have fuel pressure but what is it? It has to be 55 psi or it won't even try.

SOURCE: check engine light on

Please check the fuel line for leakage. If there are no leakages, verify that your fuel tank cover is well fixed.

Take care.

Testimonial: "THANK YOU I'LL TRY LOOKING AT THOUGHS ITEMS AND MAYBE REPLACING THE GAS CAP "

SOURCE: LOW OIL PRESSURE ON 2007 GMC SIERRA 1500. CHANGED

have it tested using a manual gage if still low then main baring ore most likely bad that would mean a over hall if is really low and bearings bad should be making rattle noise when started up first few seconds

Testimonial: "thanks alot.truck is not making a rattling noise.we did check it with a manual gauge.it read about 10 at idol. press. gets better as you incr speed"

SOURCE: My 2003 GMC Sierra Idles Rough And Cut Off

Before replacing the O2 sensors, I would check the fuel pressure. You may also try to have someone pull a trouble code from the powertrain control module to verify why the engine light is on. Do not replace any parts until this is done, otherwise your going to be guessing at the root cause, and it will get expensive with part replacement.

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SOURCE: 2006 gmc sierra 1500 4.3 . check engine light on.

More than likely the evaporator vent valve.