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Thread: Audi A3 2.0TFSI (BWA) Intermittent starting issue

  1. #1
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    Audi A3 2.0TFSI (BWA) Intermittent starting issue

    Hi all.

    I have been having this issue for some time now and would really love to get to the bottom of it.
    Car: Audi A3 2.0TFSI (57)
    Engine: BWA.

    The problem is that every morning (mainly cold at the moment, but also when outside temperatures are nice), the car fails to catch on cranking.
    After the first start of the day it is normally fine afterwards, but does sometimes do this later in the day or when I leave work it does it too.
    Once started it runs absolutely fine.

    When I turn the car over it turns well, so seems like starter is fine.
    Battery is new within the last 3 months.
    The revs raise to about 450 rpm and then drop quite low to 250rpm, but then raise again and it fires up.
    Some days it's worse than others.
    On rare occassions it needs a second crank.

    I have recently changed the following items:
    New plugs.
    New coil packs.
    New Air filter.
    Oil & Filter Service.
    New fuel filter.
    New Coolant Temperature Sensor.
    New Cam follower.
    New battery.
    Also, checked the Air Temperature Sensor with an Ohm meter and it seems that the readigns are fine when heated and when put in the freezer to cool to a low temperature.

    I do have a genuine VCDS cable and it gives me no errors on auto scan.
    All temperature sensors give a true reading when checked.
    Fuel pressures seem good, but I'm not 100% sure on that. Would the car even start if the fuel pump relay was intermittent.?
    I have carried out basic settings on Thottle Body, Intake manifold flaps and fuel pump.
    I'm now totally stumped.

    Can anyone suggest any ideas, or anyone experienced a similar problem.

    Any advice would be greatly appreciated.
    Thanks,
    Rob.

  2. #2
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    Hope this video works. It shows how it started the other day, but it's normally worse than this:

    http://s12.photobucket.com/user/bobb...vxos1.mp4.html

  3. #3
    Benevolent Dictator Uwe's Avatar
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    I understand not wanting to re-post an Auto-Scan of your car in every new thread you start, but it would help if you'd include a link to a post where there's already a scan from your car, like this.

    -Uwe-
    The engineering problems are likely insurmountable. It would be like proposing to land a rocket booster section on a barge floating in the middle of the ocean.

  4. #4
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    You absolutely right Uwe, sorry keep forgetting that.!
    Thanks for doing the link on my behalf.!
    Appreciate it.!

  5. #5
    Ross-Tech Employee Dana's Avatar
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    FSI engines are usually extremely good (borderline annoying) about telling you when a low fuel pressure problem exists ... but can you confirm/hear the electric in-tank pump running when you first open the driver's door?

    If not I wonder if the driver's door latch micro switch is faulty and not sending the comfort signal to wake the ECM.

    If so, make sure it doesn't sound sick. Another thing you may want to do if this is time based, as opposed to temp specific, would be check the live initial starting and residual fuel pressure with an actual gauge. If you try to use VCDS MVBs and this is a fuel problem simply turning the key on to communicate may prime it and fix the issue.

  6. Likes Uwe, Sharkie1976, Jack@European_Parts liked this post
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    Hey Dana.
    Firstly I'd like to say thanks for replying to my post, greatly appreciated.
    You made some valid points there.! Since owning the car for a year now, I have NEVER heard the fuel pump priming when opening the drivers door. I'm going to have a look at the workshop repair manual to check the wiring diagrams to see if it shows me any wires or switches that should be making comms with the low pressure pump. I believe it is under the rear seats but have not had a look yet. It's currently raining here in the uk (nothing unusual). Is there a way of testing the door switch, I know it activates the interior lights ok and the door open picture illuminates in the dash display. Would that be the same switch that possibly activates the LP fuel pump.? Or could there be another switch.?
    As for the VCDS I totally agree that having to have the ignition on to get connected will not help me to see pressures within the lines when it's been sitting overnight. Unfortunately I don't have a pressure tester at present, but may be able to get hold of one if absolutely neccessary.
    I'll check out the wiring diagrams (which could proves tough, for me anyway, lol).
    If anyone ekse can confirm that there should indeed be an audiable sound from the LP fuel pump, I would be very grateful.
    Thanks again Dana, I'll hopefully be back with some info over the weekend.
    Rob.

  8. #7
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    Ok, I had a look through the wiring diagrams and couldn't managed to find any switch related to a door switch. I am rubbish at wiring diagrams.!! It did show switches, but doesn't show where they are located within the car. I've managed too find the fuse (No 27) on the drivers side removable panel and fuel pump relay. Will look at the fuse tomorrow.
    I also removed the rear seat and under it is the LP fuel pump. Opened drivers door, no sound from it, turned ignition on, no sound from it. I'll have another listen tomorrow and see if I can hear it prime in the morning.
    The only reason I can think of, is that it only activates when ignition is turned to start the engine, but can't seem to find out any info if that is the case.
    Also took a look at the drivers door, and there is no switch (like a button that pushes in or out) that is activated by opening the door.
    Hope somebody with the same car can shed some light on this.
    Thanks!

  9. #8
    Ross-Tech Employee Dana's Avatar
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    Hi Rob,

    The Comfort Bus (combo of the 42: Door Elect. Driver controller, Driver's door latch switch and 46-Central Conv. module) should send that door open/wake the fuel pump signal. The switch on these vehicles isn't a spring loaded button like the good old days, the newer cars (roughly Mk4/1999 on the VW side) have a micro switch inside the door latch itself. The switch is normally called F220 in the wiring diagrams (if you need or want to locate it).

    I would check that at some point in the #42 controller, MVB 005.2 which is labeled; Contact Switch (F2),Driver Door,Range: Door Open/Door Closed

    If the readings work every time you open and close the door and the dome lights turn on/off under normal circumstances, I would not suspect the door latch is at fault.

  10. #9
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    Hey Dana.
    Thanks very much for the additional information. I did read through the workshop manual and is says that the LP fuel pump does prime when the drivers door is opened.
    It says that the motor is very, very quiet and lasts for only 2 seconds. Well, I'm not that fast, so first thing in the morning I got my wife to open the door after I removed the rear seat and held a screwdriver to my ear to amplify the sound, and it does indeed make a audiable sound. So I guess that rules out the LP fuel pump.
    So fuel supply to the engine seems to be fine. I will look at the VCDS #42 controller when I next attach it, just incase it's intermittent (you never know).
    Other than that, I'm trying to think of where to go next.
    Any pointers would be appreciated by anyone.
    All the best,
    Rob.

  11. #10
    NostraJackAss Jack@European_Parts's Avatar
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    Hello Robert........

    Well I bet you are losing a terminal 15........ either function of relay, or during the cold start with an ignition switch which is fubar in crank position, and no terminal 15 feed during the terminal 50 commencing. ( most likely )

    Be sure to observe J271 ecu supply relay during condition for 15 and terminal 30 via J317 and BUS support in engine bay supply via J757.

    Double your pleasure .........Do not omit the onboard control supply relays for terminal 30 or terminal 15 or........X J59
    ( known as supply relay 2 for both onboard supply 0x09 ) so dumb...... but hell lets complicate it further.

    A faulty ground during crank load to a cold engine......... can cause condition you aforementioned.
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