6NZ question

Discussion in 'Peterbilt Forum' started by 2000Pete379, Mar 29, 2019.

  1. 2000Pete379

    2000Pete379 Bobtail Member

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    Jun 3, 2011
    Foss, Oklahoma
    0
    I have a question about a couple trucks we have in our fleet. We have a 2000 model 379 with a 6NZ that I had flashed with a 7cz file, and a 2003 379 with the same engine, flashed with the same file. Both engines have around 400k on an overhaul. Both engines have the same injector codes. I’m not aware of any hard part differences, but that doesn’t mean there aren’t any. As far as I know, the only difference is the fls/fts settings. The 2003 truck has a very noticeable power advantage, probably in the range of 50-75hp or so, plus it smokes more when you roll into the pedal from low or no boost. Could just the difference in those fls/fts settings cause this? Thanks in advance.
     
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  3. Deere hunter

    Deere hunter Road Train Member

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    Aug 5, 2017
    Shallowater Texas
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    Are you sure the 2000 is not a 2ws.
     
  4. DieselTech_Aus

    DieselTech_Aus Light Load Member

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    Dec 20, 2017
    WA
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    they both have "hot" trim codes in them?

    if that is the case its likely the better truck has a few higher flowing injectors or the slower truck has boost leaks.

    a trim file is a pulsewidth modifier. its like a gain to balance cylinders. the ECM commands X pulsewidth at any given time. the trim file will then modify that pulsewidth to suit the injector. for example the trim code for number 1 might only allow 93% of pulsewidth to the injector. the trim code for number 2 might modify the ECM pulsewidth and send 104% of it to the injector. this allows cat to make up for mechanical flow differences between each injector and keep them balanced for equal fuel delivery in each cylinder.

    the trim files work within a resolution. they have a window. if the injector is flowing high and the trim file for that injector has used all its resolution to reduce flow down as much as possible then it cant reduce any further. opposite to that if an injector is quite low flowing and the trim file for it bumps the flow up to required volume then it cant add any more than that.

    so given that if 4 of the 6 injectors in the slower truck were low flowing and the factory trims are all adding a % to the Pulsewidth to get them up to spec, then using hot trim files on those injectors will only add a small percentage of fuel.

    if most of the injectors in the faster truck were high flowing and the factory trim were used to reduce flow to spec then using hot trim on them will make them flow significantly greater volumes of fuel in comparison to the ones that didn't flow spec from factory.

    for example the slow truck factory trim file might have been sending 110% PW to that injector to get factory flow. now with a hot trim file that might add 10% more fuel flow for that injector.

    the faster truck factory trim file might have been sending 90%PW to that injector to get factory flow. with a hot trim file that might add 20% from the middle of its resolution window resulting in 30% total additional fuel.

    the 7cz 600 file uses a long PW from factory to make power given the injector is 2.82kg/min 10r8501 same as 550 6nz. now with your hot trims you're taking an already long PW and stretching it as far as you physically can. you're doing that all through a relatively small tip without changing the start of injection point. your hot trims are holding that injector open for a far greater period of time in order to flow the additional fuel through the small tip, but the engine is still going the same speed.

    you're now pouring fuel in over a much greater section of crankshaft revolution. your start point it still the same, you've only moved the end point.

    black smoke is half burnt fuel. its from too much fuel, not enough air or poor combustion.

    in your case the black smoke is from poor combustion because you're still pouring fuel into the pot well after the piston has ran away from TDC, often to the point you'll be spraying fuel straight onto the liner and washing it. the black smoke isn't from the extra fuel you've added. its from the poor combustion of that extra fuel.

    stretching the PW with hot trims is a terrible idea and not healthy for the engine at all. if you want more juice in the pot put a larger tip injector on and keep the pulsewidth short. that way the additional fuel you want for power will be injected within the period of crankshaft revolution that it can be combusted efficiently and completely burnt in.
     
    Last edited: Apr 5, 2019
  5. spsauerland

    spsauerland Road Train Member

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    May 31, 2010
    West Harrison, In
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    Full Load Setting and Full Torque Setting number can make a big difference power. No magic numbers though, vary with flash file and personality module. 0, 0 is the field re-rate numbers.
     
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