Mis at high RPM

Discussion in '6.9L IH & 7.3L IDI Diesels' started by Bumper, Aug 1, 2018.

  1. Bumper

    Bumper Registered User

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    I have a 7.3 idi that has about 5000 on complete overhaul including injectors and IP , has been running fine until about 2 weeks ago and developled a mis or sputter at around 2400 and higher , i had the injectors pop checked of which 4 did not pass , replaced the 4 and still have same problem , i replace the lift pump , old one only had 3 psi , and fuel filter , i went ahead and replaced the other 4 injectors , still have problem , sitting still with the throttle at 2400 it makes a sputtering sound and when does i see a blueish colered smoke , thanks
     
  2. DrCharles

    DrCharles Full Access Member

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    Weak or broken valve spring(s) maybe?:dunno

    Or (if you're getting solid stream of fuel at the Schrader valve) could be problems with your overhauled IP. Is it a parts-store rebuild aka "Dupont overhaul", or from one of the Hall of Shame vendors? Hope not.
     
  3. Bumper

    Bumper Registered User

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    I dont think its valve springs as it comes and goes , and yes i tried to go cheap and got a ip from oreilly , im leaning towards the pump because it acts very much like the old pump did , i also get a knock when you have your foot into it that puts to mind of a spark knock in a gas engine
     
  4. IDIBRONCO

    IDIBRONCO IDIBRONCO

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    That's most likely your problem. You can't go cheap with the fuel system on these engines. It may work for a while, but it will always bite you in the end. The knock is also most likely fuel related. If you replaced the injectors with the same kind, you'd better go all out and replace all 8 injectors and the pump with quality ones from Conestoga Diesel (member Agnem), R&D IDI Performance, or from member Typ4 on here. It won't be cheap, but it will be worth it in the end.
     
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  5. Hydro-idi

    Hydro-idi Full Access Member

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    You have a problem with your injectors and/or injection pump.
    Scrap the Oreillys junk & contact Russ aka typ4 or Conestoga diesel for some good quality parts.
     
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  6. Bumper

    Bumper Registered User

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    Fellas i found my problem , exhaust valve guide on num 1 cyl is gone , the machine shop i had do the work knurled the exhaust guides , i knew better and now it came back to bite me , they will be installing all exhaut guides when they fix it , thanks for all you ideas on the problem
     
  7. IDIBRONCO

    IDIBRONCO IDIBRONCO

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    Have them install bronze liners in the exhaust guides to help with the wear issue.
     
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  8. Macrobb

    Macrobb Full Access Member

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    That won't cause a mid RPM miss. An exhaust guide being gone will cause this:
    - a bit of a chuffing sound.

    Your mid RPM miss is due to retarded timing in the mid range - the IP is not advancing the way it should.

    BTW, if you pull the heads, MAKE SURE to have the shop check the valve recession(bottom surface of valve to bottom surface of head). If it's out of spec by even .010", it'll be hammering on the piston and destroy the guide in short order. That's what happened to the motor in that video - Guide had about 1/16" of side-play(aka totally gone) due to hammering it's way into the piston.
     
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  9. IDIBRONCO

    IDIBRONCO IDIBRONCO

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    Also use Fel-Pro head gaskets. They are .010" thicker than the ones from Victor Reinz. I measured them both at uncompressed and compressed thicknesses using my Mitutoyo coolant proof mic. I trust that measuring device.
     

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