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What supposed to happen during a DPF regen? Diagnosing fault

Discussion in 'Engine, Drivetrain, Fuel and Exhaust' started by surfer_x, Sep 13, 2017.

  1. surfer_x

    surfer_x Member

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    Your Mercedes:
    Sprinter MWB 313 2010yr
    I have sprinter with OM-651 (2010 model) with 185K miles,

    The DPF is NOT blocked, the soot load is reported at less than 10%.

    I managed to get set up the torque app so I could monitor some parameters.

    This is what happens when a regen starts on my vehicle:

    1. the cat temp climbs to 700 degrees, (more fuel injected later?)
    2. the throttle closes to 10% what does the throttle do in diesel engine? or is the something do with the EGR?
    3. Boost is much lower, it goes negative when the engine is on the overrun.

    If a push a little to hard on the accelerator, the regen stops with a boost pressure fault, the boost pressure is not that high maybe 10 or 15 psi. If a stay in a higher gear the regen will complete, and the vehicle carries on light a freight train and pulls just under 23 psi of boot with pedal all the way down.

    My question is what is supposed to happen? and any ideas on the likely fault?
     
  2. LostKiwi

    LostKiwi Senior Member

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    Here's a summary of the process.
    You may not have all the warning lights he talks about.

     
  3. OP
    surfer_x

    surfer_x Member

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    Thanks, but that's a little basic, was hoping for more details. I understood the extra fuel added later in the cycle, (point 1) but it does not mention anything about throttle settings, waste gate or any other changes to the plumbing of the induction or exhaust, which certainly is happening for me.

    Points 2 and 3

    I suspect there is a leak, a valve is not operating correctly or sensor is not working as it should.
     
    Last edited: Sep 13, 2017
  4. monkeh

    monkeh Active Member

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    Things like glowplug faults stop a regen, Actuator faults, any sensor on the exhaust system also halt a regen.
     
  5. Steve@Avantgarde

    Steve@Avantgarde Forum Supporter Authorised Forum Supporter

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    The DPF pressure sensors are usually the real common issues
     
  6. Uncle Benz

    Uncle Benz Senior Member

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    I recently had a problem with a 651 in a C Class with 140k on it that sounds similar to yours. It would infrequently log a boost pressure fault, quite possibly during regen - I never looked that in depth into it. Another garage had changed a lot of stuff, but I noticed a sluggish response on a pressure sensor located on the intake manifold, near the egr cooler. On a hunch I swapped it with the identical one on the other side nearer the turbo and the response improved. Fitted a new one and problem solved. Not saying its the same, but could be worth looking at.
    I fully expected that car to have a broken inlet manifold bolt based on the description the owner gave on the phone, but the car would wear a full throttle blast without a boost fault so I ruled that one out early.
     
  7. moj91

    moj91 Senior Member

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    Boost pressure loss and faulty sensors also cause a regen to fail. We have a 2005 S320 with an early DPF which would not regen due to what transpired to be a split plastic cap end on the intercooler. Supposedly any faults at all with the emissions system will stop a regen.
     
  8. turbopete

    turbopete Senior Member

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    how stupid is THAT idea?? you would imagine it would be biased the other way, to regen MORE if it thinks something is amiss, to keep emissions LOW. unless, of course, its another ploy to try to get you to spend money at a dealers
     
  9. moj91

    moj91 Senior Member

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    Turbo
    pete

    I think you have hit the nail on the head there haha!! The earlier DPF systems, such as on our W220 as an (regrettably chosen) option were over engineered as compared to the newer cars which seem to be much more picky/temperamental and DPF's fail of their own accord at much lower mileages... (Like my W204) so, you know, the dealers can make some more money from you. No wonder so many people drill out the cores and have them mapped out ;)
     

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