Detroit boost issue

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by periodic, Jul 13, 2021.

  1. jamespmack

    jamespmack Road Train Member

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    What tune up procedure was used. Valve overlap, or Timing circle?
     
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  3. Rideandrepair

    Rideandrepair Road Train Member

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    I don’t know how much boost you expect to get. Mine have always been around 25-30 max. Current one with fresh overhaul and New turbo, and CAC has seen 34-35. Only a couple times. I don’t really trust the guage. The idea of 40 psi being normal? Don’t know where that came from, but I’ve heard it before. Don’t think it’s right.
     
  4. periodic

    periodic Bobtail Member

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    I don’t need 40 PSI.

    when I hook up my truck to Detroit diagnostics and go to the gauges, my ecm is only reading 17 lbs of boost, but in reality my mechanical gauge is showing 27 lbs of boost. I’m losing 10 lbs somehow.

    There’s something wrong, i can feel the truck having barely any power, combined with the 5.3 MPG. Between my mechanical gauge and what the ECM is seeing there’s something wrong.

    imgur.com
    [​IMG]
     
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  5. periodic

    periodic Bobtail Member

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    unsure. The problem was happening before my tune up.
     
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  6. Antinomian

    Antinomian Road Train Member

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    Can it be that one reading is the intake manifold pressure and the other is the amount of boost? The difference should be around 14 PSI though, not 10. Does the ECM show the correct barometric pressure?
     
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  7. jamespmack

    jamespmack Road Train Member

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    What the ecm reads is not important, your manual guage is correct.

    Go through sensor list and make sure you don't see other sensors out of range.

    You say filters and intake are good. Check cylinder temps at each manifold when cold. Seen plenty of reman injectors fail out of the box.

    Have someone who has experience double check overhead adj.

    Other than that, most mpg improvement can be improved best with driving habits.
     
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  8. periodic

    periodic Bobtail Member

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    Are you sure about the first part? Because I feel like my truck is not responding now it’s supposed too.

    I’ll check cylinder temps next weekend hopefully.

    Has been double checked by a mechanic I trust.


    I drive 68 mph at 1450 RPM on cruise. Never more than 70k gross.
     
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  9. jamespmack

    jamespmack Road Train Member

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    Yea, seen ecm read way off from gauge more than once. As long as its not setting a over boost code its still adding fuel no matter what the ecm sees. You could have a million problems. Start simple and dont over think it. Your milage seems low. But not to low. I pull covered wagon hauling steel, and pull hopper. I overload every chance I get. Mines not stock, but not wild. I average 6.5 yearly. I would check the basics and then be very honest with yourself about driving habits.

    Drive it like it has a egg under the pedal. Try running higher rpms to. With a cat, you get on a the throttle when you hit a hill. With a Detroit you get on the throttle when you see a hill. Ends up about the same.
     
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  10. periodic

    periodic Bobtail Member

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    Detroit 12.7 DDEC 4 Interesting problem

    Seems like my issue is the same as this guy and he could never figure it out either. It has half power at best, It’s night and day difference from before.
     
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  11. jamespmack

    jamespmack Road Train Member

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    But at 27psi, your not at 550hp. Your under. You say it doesn't leak. So injectors need checked. Tune up needs checked. 169011 turbo im not familiar with. Is it a waste gate turbo? Has it been tested for operation? Is it opening to soon? Things you have to check. Has fuel psi been checked?

    Lots of things to check. I'm no experienced Ddec5 guy. But a engine is a engine. Doing the best we can on a public forum not seeing it in person.
     
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