3406b low boost and fuel pressure issues

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by rs72z, May 28, 2022.

  1. rs72z

    rs72z Bobtail Member

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    95 kw 3406b
    engine has a mississippi red hot turbo, , i believe is what its called, also has ceramic exhaust manifold, was making 32 lbs of boost. Suddenly dropped down to 20. Put a fueI pressure guage on it, 40 at idle drops to 30 under boost with load and will drop down to 20 and stay a few seconds and then go back to 30. I will give a list of what all i have done to it.
    cat filters
    afrc diagprham
    primer head,
    all lines suction and return, I did find some chunks of rubber stuck in the tee for the return.
    transfer pump
    cac and 3 boots, cac had mutiple small leaks
    none of this made any difference
    I finally found 4 of the 6 intake gaskets pushed out, thought this would solve my issue. It did pickup 5 pounds of boost to 25 lbs.
    When i go to Colorado it will make 27 lbs.
    Tanks pull down even also.
    also pyro never gets over 750
    Anyone have any Ideas.
    I have thought about fuel shutoff solenoid, but havent tried taking it off.
    Thanks for any help!
     
    Last edited: May 28, 2022
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  3. AModelCat

    AModelCat Road Train Member

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    Dunno what fuel pressure's supposed to be but if it can't get fuel, it won't make boost.
     
  4. rs72z

    rs72z Bobtail Member

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    I have been told no lower than 30
     
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  5. BoxCarKidd

    BoxCarKidd Road Train Member

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  6. rs72z

    rs72z Bobtail Member

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    Replaced it
     
  7. BoxCarKidd

    BoxCarKidd Road Train Member

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    Caught that on the second reading of your post. Maybe run a supply line from it into one of the fuel filer necks and drive it?
     
  8. rs72z

    rs72z Bobtail Member

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    Never thought about that.
     
  9. Oxbow

    Oxbow Road Train Member

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    That's right where the fuel pressure runs on both of our B models. Without running a FAS type system, or custom building your own pump system like @wore out has don't think you're going to get much better. The 90 degree fitting to the return line on the back of the injection pump has a little tiny orifice in it that restricts flow and builds the pressure, but I can't see that getting bored out. If it gets plugged your pressure goes way up.

    I'll defer to @wore out as I'm not well enough versed in how they work to help.
     
  10. rs72z

    rs72z Bobtail Member

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    I pulled the return fitting out and didnt see anything wrong with it, but I don't know what size the orfice is supposed to be.
    Im worried about the drops in pressure under boost when loaded.
     
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