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1999 GMC 1500 Pickup Question: P0300

 

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HilBile2542, Noblesville, IN, November 04, 2010, 02:04
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Ok, so i am getting a p0300 code. I have changed all plugs and wires, distributer cap checked for any vacuum leaks and found the only problem i can find is with the fuel pressure. i have replaced the fuel pump twice within a week i am only getting 53 pounds of pressure and thats the best i can get out of a fuel pump??? i have no idea what to do and neither to like 10 different mechanics that i have taken it to? what do you recommend?

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  • Answer #1

    November 04, 2010, 05:11
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     Master

    Is it only a P0300? There should be other misfire codes also in the ECM. What kind of scanner are you using?
    If everything else is OK, The Crankshaft Position System Variation Learn Procedure might need to be performed. Read the TSB below:

    The crankshaft position system variation compensating values are stored in the PCM non-volatile memory after a learn procedure has been performed. If the actual crankshaft position system variation is not within the crankshaft position system variation compensating values stored in the PCM, DTC P0300 may set (refer to Diagnostic Aids for DTC P0300).
    The Crankshaft Position System Variation Learn Procedure should be performed if any of the following conditions are true:
    DTC P1336 is set.
    The PCM has been replaced.
    The engine has been replaced.
    The crankshaft has been replaced.
    The crankshaft harmonic balancer has been replaced.
    The crankshaft position sensor has been replaced.
    CAUTION: Set the vehicle parking brake and block the drive wheels when performing the Crankshaft Position System Variation Learning Procedure in order to prevent personal injury. Release the throttle immediately when the engine starts to decelerate. Once the learn procedure is completed, the PCM will return the engine control to the operator and the engine will respond to the throttle position.
    IMPORTANT: The scan tool crankshaft position system variation learn function will be inhibited if engine coolant temperature is less than 70°C (158°F). Allow the engine to warm to at least 70°C (158°F) before attempting the crankshaft position system variation learn procedure.
    The scan tool crankshaft position system variation learn function will be inhibited if any Powertrain DTCs other than DTC P1336 are set before or during the crankshaft position system variation learn procedure. Diagnose and repair any DTCs if set.
    The crankshaft position system variation learn function will be inhibited if the PCM detects a malfunction involving the camshaft position signal circuit, the 3X reference circuit, or the 24X reference circuit.
    If the scan tool indicates a problem with the Cam signal, refer to DTC P0341 Camshaft Position (CMP) Sensor Performance.
    If the scan tool indicates a problem with the 3X crank signal, refer to DTC P1374 Crankshaft Position (CKP) High to Low Resolution Frequency Correlation.
    If the scan tool indicates a problem with the 24X crank signal, refer to DTC P0336 Crankshaft Position (CKP) Sensor Circuit.
    The scan tool crankshaft position system variation learn function will no be enabled until engine coolant temperature reaches 70°C (158°F).
    Selecting the crankshaft position system variation learn procedure on the scan will command the PCM to enable CKP system variation learn fuel cutoff and allow the crankshaft position system variation compensating values to be stored in the PCM. The PCM must detect an engine speed of 5150 rpm (CKP system variation learn fuel cutoff) during the crankshaft position system variation learn procedure to store the crankshaft position system variation compensating values and complete the procedure.
    Set the parking brake.
    Block the drive wheels.
    Ensure the hood is closed.
    Start the engine and allow engine coolant temperature to reach at least 70°C (158°F).
    Turn OFF the ignition switch.
    Select and enable the crankshaft position variation learn procedure with the scan tool.
    Start the vehicle.
    Apply and hold the brake pedal firmly.
    Ensure the transaxle is in park.
    Increase accelerator pedal position until the fuel cutoff is reached at 5150 rpm. Immediately release the accelerator pedal after fuel cutoff is reached.
    The crankshaft position system variation compensating values are learned when the rpm decreases back to idle. If the procedure terminates.
    Observe DTC status for DTC P1336.
    If the scan tool indicates that DTC P1336 ran and passed, the crankshaft position system variation learn procedure is complete. If the scan tool indicates DTC P1336 failed or not run, check for other DTCs. If no DTCs other than P1336 are set, repeat the crankshaft position system variation learn procedure as necessary.

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    HilBile2542, November 04, 2010, 18:03
     Rookie

    its only the p0300 besides that code the only one i get is the ones for my abs which im ok with but it doesnt say a specific bank or cylinder so im at a loss

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    ZeeTech, November 04, 2010, 20:16
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     Master

    The P0300 means: Random/Multiple Cylinder Misfire Detected. This code usually won't set by itself. There should be least an other P030X next to it. Was it diagnosed by a real diag. tool, or a $100 code reader? Cheap scanners fails to read DTCs correctly, or wont access manufacturer specific codes.
    Take it to a shop who has real GM capable diag. tool and do the Crankshaft Position System Variation Learn Procedure.

    Zee

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    HilBile2542, November 04, 2010, 21:44
     Rookie

    ok thanks i will try that

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