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3.0tdi Slow to start in the mornings

Discussion in 'A6/S6/Allroad forum (C6 Chassis)' started by Dane, Apr 30, 2014.

  1. Dane

    Dane Had an 8L S3, a B5 RS4 now I have a B8 S4

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    Evening gents,

    The allroad is still struggling to start in the morning, it's cranks but doesn't fire for 10 seconds ish.

    I've had the battery changed and the glow plugs changed so far, I've been reading up on the inter webs and there seems to be mention of fuel pressure needing to be at 10 psi and there's a valve that commonly looses pressure over time, any one know anymore about this / want to suggest things to explore.

    No relevant fault codes start from either.
     
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  3. B5NUT

    B5NUT Well-Known Member
    VCDS Map User

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    Only things I can think of are fueling or injectors. I take it you have no issues when the engine is hot?
     
  4. Dane

    Dane Had an 8L S3, a B5 RS4 now I have a B8 S4

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    No issues starting the engine at any other point, and no driving issues either, no stuttering or holding back.

    I think it's had injector work in the past IIRC but I'll check the receipts.

    It seems to be a fairly common issue with no clear cut solution, a new starter motor seems to have worked in some cases though
     
  5. Ginge247

    Ginge247 Member

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    I don't know if you sorted it yet m8 but I have a the same problem, very intermittent though. I found this
    http://workshop-manuals.com/audi/a5...nstalling_fuel_pressure_regulating_valven276/
    I haven't done anything about it yet though.
     
  6. gupsterg

    gupsterg Active Member

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    This thread has some info about it, Link:- http://www.vwaudiforum.co.uk/forum/...had-faults-with-the-V6-TDi-fuel-return-system

    Post 9 of above linked thread have test method.

    Post 3 has some info on the other valves/sensors on common rail, if you had issues with any of those valves I'd think you'd get a DTC excluding the injector return pressure valve as that has no elec.connections. If that was faulty I'd think you'd have other issues than just slow cold start.

    N276, N290 can be actuated by a VCDS output test in engine ECU plus you can check MVB's:-

    Code:
    022 Rail pressure control
    
      1) Engine speed
    
      At idle: 720 ... 820 rpm
    
      2) Specified rail pressure
    
      [bar]
    
      3) Rail pressure actual
    
      [bar]
    
      4) Pressure regulating valve activation
    
    At idle: 15 ... 30 %
    
      - Values for warmed-up engine
    
      - Permissible difference between specified and actual value at Idle: maximum +-20 bar
    
    
    023 Rail quantity control
    
      1) Engine speed
    
      At idle: 720 ... 820 rpm
    
      2) Specified rail pressure
    
      Check values with measured value block 022
    
      3) Rail pressure actual
    
      Check values with measured value block 022
    
      4) Quantity adjuster valve activation
    
    At idle: 35 ... 48 %
    
      Values for warmed-up engine
    I think above tests would also give you an idea if G247 is ok.

    I gotta admit at times thought mine was a bit slow on cold starts and I'd gone through process of new glow plugs / injectors / battery and other bits as I'd had other issues and when my starter motor did conk out that was the biggest improvement for starting. Perhaps observing MVB data for cranking speed and comparison with another will show if starter motor weak?
     
    #5 gupsterg, Nov 8, 2014
    Last edited: Nov 8, 2014
  7. desertstorm

    desertstorm Well-Known Member
    Audi A4

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    I think the reference to the 10 PSI is possibly related to the restrictor on the return flow from the injectors. Item 9 on the diagram.

    http://workshop-manuals.com/audi/a5...ion_system_diesel_injection/injection_system/

    This actually works at 10 bar (145 PSI) page 40 in this document

    http://vwts.ru/engine/cata/pps_941803_3l_tdi_cata_w_clean_diesel_system_eng.pdf

    Karl.
     

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