MXS acert boost conundrum

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by ready2truck, Jul 28, 2021.

  1. ready2truck

    ready2truck Light Load Member

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    I have two mxs c15s. One easily boost up to 50 psi bobtail the other one struggles to get to 40. Boost measured at the ECM.
    I took it to a cat they changed fuel pump and charge air cooler and that brought it up from 28 to 38. They checked the turbos and said those are good. They said it passed injector cutout test. They ran overhead. Ivas are good. This truck does have the dome style fuel filter I don't know if that can cause fueling issues. What else should I check I'm at a loss right now.

    The one boosting to 50 psi easily is on a 550 tune the other one is on a 500 tune. But before the 550 tune I was on 475 and it was still boosting 50 easily.
    Truck with low boost only has 156k other truck has about that on a gold I frame.
     
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  3. ready2truck

    ready2truck Light Load Member

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    Could clogged mufflers cause this? Low boost truck most likely has oh mufflers other truck has Donaldson's.
    Also the gearing is 3.42 on the low boost truck and 3.55 on the other one.

    Would either of these account for a 10+psi drop?

    Had a few clamps that weren't very tight. Clamped them down tighter and it just seems like it doesn't want to build past 38-40. My other truck is a monster.
     
  4. A5¢

    A5¢ Medium Load Member

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    Just to toss this out there...air filter, fuel filter, low fuel pressure, air suction leak from tank to transfer pump, partially plugged pick up tube in tank...
     
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  5. JackZ

    JackZ Bobtail Member

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    If your truck has a catalytic converter I would suspect that is clogged. I have a 2006 Peterbilt with an MXS ACERT that had low boost and high EGT and that was the problem.
     
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  6. ready2truck

    ready2truck Light Load Member

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    Thanks for the input. It's at the shop right now getting new mufflers. Hope that's the problem. Tired of spending money. lol
     
  7. ready2truck

    ready2truck Light Load Member

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    Air filters brand new, fuel filters brand new, cat said fuel pressure was 82 before they changed the pump now it's "in spec" (didn't say psi).
    If the new mufflers don't fix it I'll start looking for air getting into the fuel. What's the best way to check for this?
     
  8. JackZ

    JackZ Bobtail Member

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    Jul 7, 2011
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    Just to be clear, the catalytic converter is different than the mufflers so if your truck has one, they need to check it to make sure it's not partially or fully clogged. How I found my problem was by taking the cat out of line for a test. The boost went up and the EGT's dropped immediately (when driving).
     
  9. ready2truck

    ready2truck Light Load Member

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    Freightliner with acert had catalytic converter built into the muffler.
     
  10. ready2truck

    ready2truck Light Load Member

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    Figured it out. The new mufflers made it spool up faster and gained 1 or 2 psi. The 550 tune took it all the way to 51psi.
    My other truck builds boost faster probably because of the 3.55 and low pros. That #### thing can get 48psi easy grabbing gears on the high side bobtail.

    Thanks for all the helpful posts.
     
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  11. ready2truck

    ready2truck Light Load Member

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    Should I change this to a cat housing or just change out the 90° fittings?

    Do these style of fuel filter restrict the flow of fuel?
     

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