3406B 4MG Low power

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by Sublime, May 30, 2018.

  1. Sublime

    Sublime Road Train Member

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    I have 3406B 4MG in my '89 T600.

    It's kind of gradually lost power in the last couple months.

    Gauges all show normal temps. Fuel pressure gauge above 30 psi, filter restriction gauges normal. Oil pressure is normal. Fuel and air filters are new.

    It won't boost til hitting 1700-1800rpms. Until then it's only about 7.5psi. Throttle pedal movement does nothing.

    Before this change I used to upshift at 1700 rpms fully loaded and it would keep going. Now I upshift and it takes forever to get up to speed with only 7.5psi til I hit 1800 again.

    Going down the road it's not too bad til I hit an uphill and it just drops off, won't pull even mediocre MN hills.

    It feels almost like an old car with a bad accelerator pump.

    Pic for attention but it has CAT filters and new ATA boots on it now.
     

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  3. swaan

    swaan Road Train Member

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    Check the diaphragm in the air/fuel ratio control valve. Its prob got a hole in it.

    Easy fix
     
  4. swaan

    swaan Road Train Member

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  5. Sublime

    Sublime Road Train Member

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    We have a good mechanic here who does ISX and S60 rebuilds, is this something he could do with the proper info?

    Is that the Fuel Ratio Control?
     
  6. swaan

    swaan Road Train Member

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    That's what I said in my reply yes.

    It's not hard to fix. Its perty self exsplanitory once you take it apart.
     
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  7. Sublime

    Sublime Road Train Member

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    Sorry, somehow I scrolled right past your reply. Thanks!!
     
    swaan Thanks this.
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