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Misfire at 3-4k. How to find and resolve?

Discussion in 'A3/S3 Forum (8L Chassis)' started by Bad Sir Culation, Jan 12, 2014.

  1. Bad Sir Culation
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    Bad Sir Culation Member

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    [Jan 12, 2014]
    As mentioned in my fault codes thread, the injectors are all showing an pen circuit. Could this affect the car enough to cause a misfire at 3-4k at around 3/4 throttle or above?

    Also, I found a melted connector plug for my N249 and the N249 itself has vanished. Unfortunately it's been left hanging at the back of the engine as I have obviously forgotten to cable tie it up and it's sat right against the block by the looks of it.

    Would the N249 not being connected be a possible cause of either the misfire or the charge pressure exceeded faults?

    I can't think of anything else, unless the map on the car is dodgy, but I have no way of knowing that. It definitely doesn't misfire at anything up to half throttle though. It can be quite severe too. I need to find the root cause of this issue. I feel like we are finally making some headway now.
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  3. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    [Jan 12, 2014]
    The ECU needs to see something connected to the N249 plug else adaption and fuel trims won't work... this can lead to over fuelling on idle as the ECU won't compensate correctly


    The fact that you have misfires and open circuit fault codes on the injectors suggests this is related... I would be starting by tracking down your electrical gremlins before worrying about anything else... the codes are thrown for a reason... open circuit is effectively switching the injector off... injector off = no fuel, no fuel = misfire...


    Once you are fault code free then revisit the misfire issue but I suspect fixing the electrical gremkins will sort this out

    <tuffty/>
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  4. JudderMan
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    JudderMan Active Member

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    [Jan 12, 2014]
    But the N249 is usually at the front of the engine....or am I missing something here?
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  5. Bad Sir Culation
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    Bad Sir Culation Member

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    [Jan 12, 2014]
    It isn't on the APY. It's nearer the top.
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  6. Bad Sir Culation
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    Bad Sir Culation Member

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    [Jan 12, 2014]
    Thanks Tufty, this is a nightmare!

    Actually, there is a fault for the N249 (obviously!) but there is also one listed as:

    17925 - Power Supply Relay for ECU (J271 or J363)
    P1517 - 35 - 10 - Electrical Malfunction - Intermittent

    I need to find out what that is and whether it's also related.
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  7. Bad Sir Culation
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    Bad Sir Culation Member

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    [Jan 12, 2014]
    Really struggling to find out where this J271 relay is, or what the part number is to buy a replacement......

    I also can't find anything on ECP for an oil temp sensor, another item which threw a code.
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  8. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    [Jan 13, 2014]
    Engine control relay... its in the little black box on the passenger side of the bulkhead next to the trunking that goes into the scuttle..

    I still think you have wiring issues rather than loads of stuff actually wrong... have you checked the earths under the battery tray?

    I have a wiring diagram for an APY ECU... pm me...

    <tuffty/>
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  9. Bad Sir Culation
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    Bad Sir Culation Member

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  10. Bad Sir Culation
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    Bad Sir Culation Member

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    [Jan 13, 2014]
    I haven't yet checked those earths. Might be next weekend now. I can't see the one for the coils either.
    #9
  11. s3dave
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    s3dave TFSI Hybrid

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    [Jan 13, 2014]
    Also check the coil pack loom, they are well known to go brittle and crack the insulation off under the black tape, Awesome do a replacement loom for this and is well worth doing if in doubt..
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  12. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    [Jan 13, 2014]
    In this picture... the earth point is between cyls 1 and 2

    [​IMG]

    <tuffty/>
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  13. Bad Sir Culation
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    Bad Sir Culation Member

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    [Jan 13, 2014]
    Does it include the earth? Any link at all?

    Tufty, almost certain that's missing.
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  14. s3dave
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    s3dave TFSI Hybrid

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  15. Bad Sir Culation
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    Bad Sir Culation Member

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    [Jan 13, 2014]
    Thanks Dave. It says that it's unsuitable for the 210bhp engine though.

    I presume my car does have an oil level sensor?
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  16. vroomtshh
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    vroomtshh Active Member VCDS Map User

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    [Jan 13, 2014]
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  17. Bad Sir Culation
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    Bad Sir Culation Member

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    [Jan 13, 2014]
    I might be being a dumbass, but I don't know if I have the oil level sensor? VCDS gave a code for an oil temp sensor at the last scan. Must therefore have one of those, but couldn't find one on ECP.

    Do you know of a loom for the APY engine?
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  18. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    [Jan 13, 2014]
    APY comes with an oil sensor in the sump... its used for temp and oil condition for AVS servicing

    As I have said to you on this and the other threads mate... your problems are not sensor related they are wiring related... you need to start tracking back the loom as there will be a common fault for all these sensors... a broken supply wire, earth or even the engine management relay...

    Don't buy any new sensors etc until you have tracked down your wiring gremlins... there are a few cars being broken in the classifieds and no doubt a few on eBay... see if you can grab a complete engine loom if its cheap enough

    <tuffty/>
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  19. Bad Sir Culation
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    Bad Sir Culation Member

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    [Jan 13, 2014]
    Doh, yes I remember that now from having the sump off.

    Whole loom seems excessive but I think you're right and it's probably the best move.
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  20. Bad Sir Culation
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    Bad Sir Culation Member

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    [Jan 14, 2014]
    Bought an APY engine loom. £60 posted. Fitting that will take some research!

    Not even sure where ECU etc are or exactly where all of the earth points are besides the ones I've recently been told about on here.
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  21. vroomtshh
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    vroomtshh Active Member VCDS Map User

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    [Jan 14, 2014]
    ECU is under the scuttle panel.

    Earths are under the battery and on the gearbox mounting, plus some smaller ones dotted around
    #20
  22. Bad Sir Culation
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    Bad Sir Culation Member

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    [Jan 17, 2014]
    Fitting the loom will be fun with very little clue!

    On a brighter note, since putting an N249 back on (just electrically) and putting some Redex in the car, the misfire seems to have gone!
    #21

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