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  1. #1
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    Default troubleshooting p0300 random/multiple cylinder missfire

    i have gone through just about everything that this code could possible be caused by. at least that i think it could have caused this code to show up. my truck is running pretty bad like its not getting enough fuel around 3500rpms is when it starts. when i start it after it has cooled down it seems to idle right and when i give gas its good until it takes a load or when put into gear. then the check engine light flashes and throws that p0300 code. i have changed the following.

    wires
    plugs
    EGR
    IAC
    CAM potion sensor
    cleaned the MAF
    changed out my O2s
    fuel filter
    ran injector cleaner
    checked for vacuum lines for leaks
    changed put fuel pressure regulator
    made sure that i had spark from the coil pack each one seems good

    HEEEEEEELP!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

  2. #2
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    Have you checked the fuel pressure yet. Multiple cyl misfire could easily be because it's intermittantly lean from insufficient fuel delivery. I see you put an FPR & a fuel filter on it, but an FPR won't fix it if the pump isn't delivering enough quantity to begin with. I would get a guage from AutoZone (they loan them out for free) & check fuel press before you spend any more money.
    1988 Chevy C-3500 2wd (no pic)
    350 c.i. 5.7 L Stock Block, 4 Bolt Mains
    L-31 Vortec Heads, Edelbrock Cam & Intake,
    Holley 650, Flowtech Headers, Magnaflow exh.
    Jet Trans 700R4, B&M Ratchet, 4:10 gears,
    3" susp. lift kit "shadetree"
    No rev limiter, No speed limiter lol


  3. #3
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    murdog94's Avatar
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    Default

    Agreed that you need to look at the fuel pressure, you also need to look for a vacuum leaks around the intake gaskets etc... also do a little searching here on the site there quite a few threads on here reguarding the PO300 code. and people had problems with anything from fuel pressure to knock sensors.
    Mike

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    1997 Chevy S-10 Blazer 4X4 with 330K miles and counting (Hunting rig).

    2009 Saturn Aura XE (wifes car)

    2011 F-150 Crew 4X4

    "Hold it to the floor till you see God.... Then Brake!!!!"

  4. #4
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    Default

    today i replaced the intake gaskets, and made sure while i had the intake off to open up the value covers. WELL i can mark that off the list... it didnt help at all who would have guessed, i had to do it i didnt feel like droping the tank today if it does turn out to be the pump. but back to your question i have not checked the pressure YET. im now left with this step i figured that i would have to do this but was hoping that it wasnt the pump. oh well you live and you learn right.
    do you think that it would be the PCM causing this issue???
    2001 chevy
    z71 1500
    5.3l silverado
    bully dog programer

  5. #5
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    not likely, i would lean more twards a fuel related issue...
    Mike

    Currently

    1997 Chevy S-10 Blazer 4X4 with 330K miles and counting (Hunting rig).

    2009 Saturn Aura XE (wifes car)

    2011 F-150 Crew 4X4

    "Hold it to the floor till you see God.... Then Brake!!!!"

  6. #6
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    i guess it time to change the pump then... OH JOY!!! "sarcasm" if you couldnt tell lol. i will start with checking it but i kinda leaning towards the pump myself at this point in the game. never had to chase down a misfire like this one before. the list is long and gets longer ive done everything that i could think of and what others have suggested on the other posts here and nothing yet gonna try the pump

    ---------- Post added at 12:23 AM ---------- Previous post was at 12:20 AM ----------

    i did throw another code fuel system running lean dont remember but think it was p0145 or something but didnt get it today.

    ---------- Post added at 12:26 AM ---------- Previous post was at 12:23 AM ----------

    could it be something wrong with my intake manifold itself just a thought
    2001 chevy
    z71 1500
    5.3l silverado
    bully dog programer

  7. #7
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    well before you spend the money on a new pump, get it checked out. But no the intake problem isnt likely.
    Mike

    Currently

    1997 Chevy S-10 Blazer 4X4 with 330K miles and counting (Hunting rig).

    2009 Saturn Aura XE (wifes car)

    2011 F-150 Crew 4X4

    "Hold it to the floor till you see God.... Then Brake!!!!"

  8. #8
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    whats your thoughts on the chance that it could be a clogged cat?

    ---------- Post added at 12:56 AM ---------- Previous post was at 12:51 AM ----------

    gonna work on the fuel side and see how it goes will keep poeted
    2001 chevy
    z71 1500
    5.3l silverado
    bully dog programer

  9. #9
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    A clogged cat will feel more like someone has attached a boat anchor to your truck. A cat shouldn't act like a misfire that you can feel as individual misses. It would be more of a no power or underpowered feeling.
    1988 Chevy C-3500 2wd (no pic)
    350 c.i. 5.7 L Stock Block, 4 Bolt Mains
    L-31 Vortec Heads, Edelbrock Cam & Intake,
    Holley 650, Flowtech Headers, Magnaflow exh.
    Jet Trans 700R4, B&M Ratchet, 4:10 gears,
    3" susp. lift kit "shadetree"
    No rev limiter, No speed limiter lol


  10. #10

    Default

    You haven't change the Crank Sensor, they can cause all sorts of problems. I would do a fuel pressure test, but you would likely have detonation along with knock sensor codes.

    What kind of plugs are you running? What gaps? What kind of air filter?
    When you hear hoofbeats, look for horses not zebras.

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