Question about GMC Sierra 1500

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I recently did a tune up on my pickup and it still has the random misfire code vehicle runs like ****. the guy at autozone says that the computer doesnt know that i have repaired the problem but he didnt tell me how to reset the computer

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  • billy wellington Oct 04, 2010

    the vehicle is a 1996 gmc sierra 1500 with a 350 vortec. the engine is missing bad and all u can smell is raw gas. i changed out the plugs, wires, cap, rotor, and airflow sensor. sounds like there is a vaccum leak at the throttle body but it,s not coming from any of the vaccum lines its coming from the throttle body.

  • billy wellington Oct 04, 2010

    by the way yes the code was po300

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If the engine still does not run right then clearing the check engine light or MIL (Malfunction Indicator Light) will not change the way that the vehicle will run, and if the vehicle is not running properly then the MIL will just come back on. You can clear any DTC's (Data Trouble Codes) by removing the fuse to the ECM (Engine Control Module) for three minutes, or also by dis-connecting the battery for three minutes, but then the radio and any other KAM's (Keep Alive Memory) will be lost and will have to be reset.

What exactly is the vehicle and engine that you are working on, and what have you done to it so far in the way of tuning it up?

Was the DTC P0300?

Posted on Oct 03, 2010

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  • Zaraki Oct 04, 2010

    The problem sounds like a leaking plastic fuel line under the upper intake manifold or "plenum".



    The Vortec engines were notorious for those kind of problems. The problem will be under the upper-intake manifold, and the fuel injector assembly will either have a cracked plastic fuel line running out to one or more of the fuel injectors, or the fuel pressure regulator that is located on the end of the fuel injector assembly is faulty or it has detached from the fuel injector assembly. Either way the lower intake manifold will be flooded with fuel anytime that the fuel pump runs.

    There were two types made, the first type had fuel lines that connected to the lower intake manifold, and then from the metal fittings the fuel line turns into plastic and runs inside the lower intake manifold and under the upper-intake manifold where it runs over to the fuel injector assembly, and this type can really flood out an engine when it becomes faulty.

    The second type had metal fuel lines running over the upper intake manifold and they connected to the top of the fuel injector assembly, however, under the upper-intake manifold there are still plastic lines to the fuel injectors and also the fuel pressure regulator that could be faulty and cause the engine to severely flood.

    The upper-intake manifold is not that difficult to remove, and after you remove the upper-intake manifold then (replace the fuel lines to the fuel injector assembly if it is the second type) turn the ignition to the "Run" position and when the fuel pump runs you should see where the fuel is leaking/spraying from, and it will most likely be a large high pressure leak from a ruptured plastic fuel line.

    Let me know if you require any further assistance.





















    Here is a firing order diagram to be certain that the spark plug wires are connected properly.




  • Zaraki Oct 04, 2010

    There is on "O"-ring at the top of the fuel injector assembly that should be lubricated with engine oil before installing the uppter intake manifold or plenum to prevent damage to the o-ring seal. Be certain that the o-ring does not get damaged when installing the upper intake nanifold or plenum, and it sounds like it might already be leaking and damaged.




  • Zaraki Oct 04, 2010

    Here is the procedure to remove the upper intake manifold or plenum, and here is also a link for a .pdf on the procedure if you would like to have it. This procedure is only for the removal and installation of the upper intake manifold, and be certain that if removing the fuel injector assembly from the lower intake manifold that the fuel injector nozzles are replaced back into the correct cylinders on the lower intake manifold and they are marked on the fuel injector assembly, and they must be routed to the correct cylinders, and if the cylinders are not marked on the lower intake manifold then use the firing order diagram to properly identify each cylinder, also the fuel lines will be brittle and hard and will most likely break easily but any relacements will not be that way, and let me know if you require any further assistance.



    http://ww2.justanswer.com/uploads/carfix...







    Removal:



    1. Disconnect the battery negative cable from the battery.



    2. Remove the air cleaner assembly.



    3. Remove the wiring harness connectors and the brackets and move aside.



    4. Remove the throttle cable and the bracket from the upper intake manifold.



    5. Remove the cruise control cable, (if equipped).



    6. Remove the fuel lines from the intake to the rear of the block.



    7. Remove the ignition coil and the bracket. Remove the upper intake manifold.



    Installation:



    1. Install the upper intake manifold gasket into the upper intake manifold.



    2. Install the upper intake manifold, and be certain to lubricate the o-ring for the fuel injector assembly and the inside of the upper intake manifold where the fuel injector assembly fits through the upper intake manifold with engine oil to help prevent damage to the o-ring on assembly, and use care not to pinch the injector lines between the upper and lower intake manifolds.



    3. Install the upper intake manifold bolts. Note the marks made at disassembly for proper stud location. Install the two corner studs first in order to help align the two halves. NOTE: Other than the two torque passes listed below, the OE Manufacturer did NOT address or supply a bolt tightening sequence for the upper Intake Manifold for this model year, or other model years where this 2 piece manifold setup is used. A "Play It Safe" final tightening sequence would be to tighten from the center most bolts to the outer most bolts.



    4. Tighten the bolts in two steps: a. Tighten the bolts on the first sequence to 5 Nm (44 inch lbs.). b. Tighten the bolts on the final sequence to 10 Nm (88 inch lbs.).



    5. Install the purge solenoid and bracket. Refer to Powertrain Management.



    6. Install the ignition coil and bracket. Refer to Starting and Charging.



    7. Install the PCV hose et the upper intake manifold.



    8. Install the fuel lines from the intake at the rear of the block.



    9. Install the cruise control cable (if equipped).



    10. Install the throttle cable and bracket from the upper intake manifold.



    11. Install the wiring harness connectors and brackets.



    12. Install the air cleaner assembly.



    13. Connect the battery negative cable assembly to the battery negative terminal.






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