Please help Paccar

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by Thrillbilly, Jun 29, 2020.

  1. Thrillbilly

    Thrillbilly Bobtail Member

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    Jun 29, 2020
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    2016 paccar mx13 deleted, no codes.
    Under a load accelerating truck builds manifold pressure past 32 PSI. When it does this it feels like it derates or loses boost. If I release the accelerator pedal, the RPMs drop and so does the manifold pressure, then I reapply accelerator pedal and I have full power until the manifold pressure reaches 32 PSI again then I lose power. Additionally, the engine doesn't want to rev above 1500-1600 RPM when I'm having the problem. Have this problem 90% of the time other 10% runs perfect. It had this issue before the delete. Has a new manifold pressure sensor, turbo actuator replaced and DPF filter media removed. Any help is appreciated.
     
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  3. tnevin225

    tnevin225 Road Train Member

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    Do you have a Exhaust temp gauge?
     
  4. Ruthless

    Ruthless Road Train Member

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    Cac leak, boot leak id look there first.
     
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  5. Thrillbilly

    Thrillbilly Bobtail Member

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    No I don't.
     
  6. Thrillbilly

    Thrillbilly Bobtail Member

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    Why wou
    Why would a cac leak cause manifold pressure to increase? It goes up to 40 PSI and stays there until I let off the pedal.
     
  7. Ruthless

    Ruthless Road Train Member

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    Itll increase, just it isnt going into the engine. Expanding psi can stretch open a small crack/leak into a big one. a pyro gauge will tell you if its getting suddenly hotter, which would tend to indicate lack of cooling air into the engine.

    its cheap to check boots and cac before you dig deeper.

    Also, if you have it tuned, but are using a stock turbocharger, you may be making more boost at an ineffective range/ higher psi but with not enough volume. Idk what turbo paccars use, or what the effective boost range is. A baby could breathe thru a straw, a grown man would slowly run low on o2 saturation of the blood breathing thru a straw. But a grown man would be pushing n pulling a higher psi through a straw than a baby would.Bigger demand for air may require a (larger) different charger.
     
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  8. Thrillbilly

    Thrillbilly Bobtail Member

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    That makes sense. That's a great explanation too. I had the issue well before the delete/tune, but much more infrequently.
     
  9. Thrillbilly

    Thrillbilly Bobtail Member

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    Would that also cause it to not rev up past 1500RPM?
     
  10. pushbroom

    pushbroom Road Train Member

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    Get it on a laptop, it most likely has codes that wont show on the dash.
    Replace the exhaust manifold pressure sensor and remove the tube and clean it. Leave the sensor out and run the motor to verify exhaust flow to the sensor.

    Remove the linkage from the bpv and wire it open.
     
    spsauerland Thanks this.
  11. pushbroom

    pushbroom Road Train Member

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    Intake manifold pressure reads at the head, if a charge air boot/cooler was leaking it will drop in pressure.
     
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