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missing at high rpms?

Discussion in 'The Garage' started by tecton, May 2, 2004.

  1. tecton

    tecton 1/2 ton status

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    truck seems to want to miss/sputter/backfire around 4-5000rpm
     
  2. micah

    micah 1/2 ton status

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    Could be fuel delivery problem. The stock manual fuel pump has a hard time keeping up at those rpm's. Or it could be time to rebuild the distributor.
     
  3. 1-ton

    1-ton 1/2 ton status Premium Member

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    I would vote for ignition since it is happening at higher RPM's, but I don't count fuel system out either.
     
  4. gm guy

    gm guy 1/2 ton status

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    Check your timing at idle and overal @ 3500 rpm. Maybe the vacume advance on your dist is not funtioning. /forums/images/graemlins/k5.gif
     
  5. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    I'm willing to bet you have one or two dying wires. They always show up under load at higher RPMs...
     
  6. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    Are you running stock HEI with stock replacement parts? Stock HEI isn't too good at high RPM's. To get the best RPM range out of HEI you must upgrade the coil. /forums/images/graemlins/k5.gif
     
  7. gm guy

    gm guy 1/2 ton status

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    Good tip. I'll get a better coil too!
     
  8. diesel4me

    diesel4me 1 ton status Premium Member

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    I hate to be a pessimist,but if its a chevy and it breaks up at high rpm and its not the plugs,wires,cap,rotor,or a fuel problem as already stated--its time to check for a round lobe on your camshaft--nearly every small block I've owned had(or still has! /forums/images/graemlins/whistling.gif)a bad lobe.Usually its an exhaust lobe that wears.This causes a backup of exhaust gas in that cylinder,and when the intake valve opens,the leftover exhaust tries to escape into the intake and out the carb,or throttle body--and it screws up the other cylinders by interfering with the flow of fuel/air mixture to the other cylinders.If you take off the air cleaner and rev it up high in neutral,you'll hear a gargling sound,and perhaps backfiring through the carb--that means its time for a new camshaft and lifters.Hope I'm not right in your case--Good Luck! /forums/images/graemlins/crazy.gif
     
  9. tecton

    tecton 1/2 ton status

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    the engine just turned 20,000miles since it was built two days ago

    cam would wear out that fast? /forums/images/graemlins/thinking.gif

    distributor was replaced some time ago....mabye end of last year
     
  10. gm4x

    gm4x 1/2 ton status

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    [ QUOTE ]
    the engine just turned 20,000miles since it was built two days ago

    cam would wear out that fast? /forums/images/graemlins/thinking.gif

    distributor was replaced some time ago....mabye end of last year

    [/ QUOTE ]

    What about valve job at time of rebuild? Valve springs (rate) checked (or springs replaced?) Possible valve "float" at higher RPM?

    20,000 miles on motor after a 2 day ago rebuild? /forums/images/graemlins/yikes.gif
     
  11. GMCLegacy

    GMCLegacy 1/2 ton status

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    he is saying: two days ago it turned over 20,000 miles since the rebuild....i think
     

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