Question about 2003 GMC Sierra 1500

6 Answers

Runs rough and almost stall on the first start of the day

When i start the truck after its been sitting overnight it feels like it wants to stall. and the check engine light will flash. now if i dont stomp the gas then the light will stay on and pop a po300 random multiple misfire. and if i stomp it the light will stop flashing. the truck will run like a champ all day weather the light stay or goes. ive changed the plugs and plug wires, fuel filter, 6 is missing more than the rest so i swapped the cols and injectors to other cylinders and got no love, and the intake manifold gasket, i was told to check the egr valve but this model doent have one so i checked the pcv valve for the rattle and it didnt. when i went to change it the valve was hollow (no guts) and the replacement looks totally different and fits the elbow but not the engine it is the 4.8 L V8 Heeeeeeeeeeeeeellllllllllllpppppppppp

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  • gmalways Jul 11, 2008

    and my mechanic tried to do a variance valve timing relearn and it would not do that either

  • gmalways Jul 11, 2008

    my truck use's coil packs so it is impossible to cross wires and the truck had the fuel pump replaced at 67,000 miles and it has 83,000 on it now so i highly doubt its the fuel pump but i have seen crazier things happen

  • Anonymous Mar 23, 2014

    valve cvr replaced ,oil filter,oil hose w elbow~stilling running out we were told to check the timing gasket~Thank You!

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6 Answers

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Hi,

It is highly probable that Sierra has a catalytic converter issue. A couple of things to check:
1. dents, holes (puncture), cracks or other damage(s);
2. no discoloration (due to high temp);
3. exhaust sensors (HO2S) (both) as well as the electrical connections/wirings;
4. clogged or rattling (would require converter to be removed).

You can verify with a scan/reading and see if P0420 and/or P0430 also shows.

Hope this be of initial help/idea. Pls post back how things turned up or should you need additional information.

Good luck and kind regards.

Thank you for using FixYa.

Posted on Jul 11, 2008

  • Louie  Role
    Louie Role Jul 11, 2008

    BTW, the PCV (Positive Crankcase Ventilation) valve is only meant to ensure that the air/pressure inside the engine (crankcase) has a means of escaping at the same time preventing air to come in the engine through that opening.

    Your concern "fits the elbow but not the engine", you can always trim the excess rubber to make it fit as it will only keep it in place but not hold back any pressure.

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Sir,

First scan the PCM for trouble codes using a hand held engine scanner, Then repair codes by replacing failed sensor as needed. If no codes are present then try replacing the fuel pressure regulator.

May be cause by the fuel pump. Replacing it and the fuel filter to repair your problem.



thanks
good luck

"Don't forget to rate the solution"

Posted on Jul 11, 2008

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Did you check the replacement part is for same model and make usually there is a difference bw the same model and different make (year), Please check it ......

Posted on Jul 11, 2008

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Are the sparkplug wires connected to the correct cylinder heads? The firing order may be off. Just a thought... The fuel pump may also be going out.

Posted on Jul 11, 2008

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How many miles are on the vehicle? Have you had the codes checked? What codes are being thrown? Definitely could be a few things at this point.
Thanks,
Lee

Posted on Jul 11, 2008

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  • Lee A.
    Lee A. Jul 11, 2008

    Clean out the TPS and see what that does.
    Let me know,
    Lee


  • Lee A.
    Lee A. Jul 11, 2008

    What are the codes being thrown?
    Thanks,
    Lee


  • Lee A.
    Lee A. Jul 11, 2008

    Have you tried cleaning the TPS?
    Thanks,
    Lee


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Check the throtle positioning sensor, or the cam sensor.

Posted on Jul 11, 2008

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