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Cam Shaft Sensor/ Starting Problems

Discussion in 'A3/S3 Forum (8L Chassis)' started by ben_turbo1, Jan 28, 2010.

  1. ben_turbo1
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    ben_turbo1 Member

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    [Jan 28, 2010]
    Hi Guys,

    Need some help again.

    The story is that my S3 had a cracked head so the garage have fitted a new one. Once they put it all back together they said it started up straight away and ran very well. But then it developed a fault and will only start 1 in 5 attempts. They have scanned the car and the fault that comes up is Cam shaft sensor below threshold. So they fitted a new sensor but this hasn't solved the fault, they then took the cam cover off and checked the timing and tensioner etc and it is all ok.

    Any ideas what the problem would be?

    I just want me car back now.

    Thanks in advance.

    Ben
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  3. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    [Jan 28, 2010]
    I assume they align the timing chain up right? there are 2 timing marks on the camshaft caps right next to the chain... did they fit the VVT back on correctly and connect it up?

    <tuffty/>
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  4. ben_turbo1
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    ben_turbo1 Member

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    [Jan 28, 2010]
    Well they said they did align it up right and have since taken it apart and double checked. But I will mention the 2 timing marks to them and see what they say.

    When I was there yesterday it started up after a few attempts and ran fine on tickover, I then turned it off and tried starting again when it next fixed up it did miss fire once, not sure if that has anything to do with it or could help any one make any sense of it.

    So you think it is deffo something to do with the timing chain/ VVT?

    Could it be anything to do with the new head I brought?
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  5. 1animal1
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    1animal1 The Clar!! it mouves!!! VCDS Map User

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    [Jan 28, 2010]
    is the cam shaft sensor the same as the knock sensor? if not it could be that but that would be an educated guess based on my experience with mine and similar symptoms

    also if the knock is the same....i had a part supplied for a golf which i was assured by a VAG specialist was the same for the S3...turns out not and i replced the new part with an actual S3 part which solved everything
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  6. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    [Jan 28, 2010]
    Was the head a pukker AMK one?

    Not sure its the chain tbh, just trying to eliminate potential issues... do you know the exact fault code?

    One thing you could check is all the earth straps and earth points as a lot of electrical issues can be caused by dodgy earths

    <tuffty/>
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  7. ben_turbo1
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    [Jan 28, 2010]
    Hmmm this really could be a bag of worms.

    I'm not sure if the knock sensor is the same as the cam shaft sensor to be honest, I will mention this to the garage. The one we replaced it with was one from Eurocar parts which may not be an OE replacement.

    When I brought the head they assured me it was the correct one although it was not stamped with any engine code. I asked them if it was an actual Audi part and they told me they can't legally advertise it as an audi made part but that it did come out of the same factory.

    I will also ask them if they have checked all the earth straps/ points.

    I have alot of confidence in the guys at the garage but I can't help but worry that this could take ages to sort.
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  8. 1animal1
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    1animal1 The Clar!! it mouves!!! VCDS Map User

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    [Jan 28, 2010]
    yup euro parts strap line 'its all made in same factory' even if its not...... hence why the brakelight switch from the dealer will outlast the euro one 8 to 1

    my knock sensor is still a pattern part, but specific to my model with one letter difference from memory..... the knock sensor is located under the oil filter..... i think the cam sensor is to the right of the top of the engine if my memory serves
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  9. ben_turbo1
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    ben_turbo1 Member

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    [Jan 28, 2010]
    Yep the cam and knock sensors are different so something we can look into.

    My guess is that it is something electrical as when the car does start it runs really well so it must be something electrical that stops it from starting.

    I will keep this thread updated as and when we find the problem but in the mean time if anyone has anymore ideas your help would really be appreciated.

    Thanks
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  10. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    [Jan 28, 2010]
    The head castings are pretty much the same across the board tbh... only real differences are the SAI hole next to the water housing which AMK/BAM don't have and small/large ports...

    I assume they reused your old cams etc?

    Did they remove the engine to rebuild it or just head off block in car?

    Knock sensors are on the block...

    Did the scan bring up any other fault codes? this could be the symptom of another fault rather than a fault in its own right... hence the earth strap stuff...

    <tuffty/>
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  11. ben_turbo1
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    [Jan 28, 2010]
    The head I brought was supplied with a blanking plate for the SAI hole which we have fitted.

    Yep they re-used my old cams, the head I brought came with news valves already installed so we didnt have to change them over from the old head.

    No they did not remove the whole engine, the just took the head off and replaced it with the new one. So I guess they wouldn't of gone anywhere near the knock sensor.

    They showed me the print out from the Bosch diagnostics machine and the only fault it showed was the cam shaft sensor one.

    I just spoje to the michanic and mentioned all the points you brought up and he said he has already checked those things and they are all ok.
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  12. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    [Jan 28, 2010]
    Hummm... I would be tempted to check the wiring at this point then... I had a bizarre knock sensor fault come up on mine before I did the BT conversion... tried allsorts like swapping the sensor over etc without success... ended up running new wires back to the ECU and that cured it

    <tuffty/>
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  13. ben_turbo1
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    [Jan 29, 2010]
    Ok it looks like we may have found the problem. The cam chain hasn't been set correctly and is only 15 links between the pulleys and not 16 like it should be, apparently they need a tool they havent got to sort it out so we wont know for sure untill monday when the tool arrives.

    Thanks for the help everyone
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  14. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    [Jan 29, 2010]
    ...smug mode on.... ;P

    <tuffty/>
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  15. ben_turbo1
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    [Jan 29, 2010]
    Do you think it would of caused any damage being run with it like this?
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  16. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    [Jan 29, 2010]
    Has the potential too... cam timing will be out and valves 'could' be close to the pistons and touch as they may not be fully closed when the piston is at the top... Hope it isn't for your sake though... all you need really...

    Fingers crossed for you...

    <tuffty/>
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  17. S3-Andy
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    S3-Andy Member

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    [Jan 29, 2010]
    i think you will get away with that error, it would appear to only be a small margine, lucky it could have been a disastor! on the plus side least u have a spare set of valves if needed, hope uyou get it sorted soon mate.
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