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2007 audi s3 misfire under boost

Discussion in 'A3/S3/Sportback (8P Chassis)' started by Poma7, Dec 12, 2013.

  1. Poma7
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    Poma7 New Member

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    Hello all, I'm new to this forum and this is my first post, although I have been reading through the forum with great interest for afew months now. An excellent forum I must add! Right.. I bought my car approx 3 months ago, and I must say I love it! It's a car known on here nobbers old one white s3 with lovely mods it's running a custom map but is approx stage 2+ The problem started as a hesitation at approx 5k revs (under boost) so after reading on here I found posts which suggested to change the coils, I've changed all 4 and it's still the same. Again after further research on here I changed spark plugs, all 4 changed for new oem plugs (originals car came with are denso racing plugs) the oem plugs were still the same at first hesitation at 5k rpm but then after afew days it wouldn't boost at all with this plugs in... Back to the forum for more research and found a very helpful thread on spark plugs and coolness levels etc, so I purchased a set of ngk iridium xi plugs 1 degree cooler as recommend for stage 2+ in the spark plug post on here. Now the car misfires randomly under boost, and it's a lot worst with these plugs in, I have taken a plug out after a day and it is quite black. I have also purchased a vagcom from the bay and no engine faults showing other than maf which I disconnected to rule out as seen in yet another forum post! Maf fault cleared straight away. As you can see I have tried to research on the forum first and have spent quite a lot ruling out things and still none the wiser! Any help would be greatly appreciated thanks gary
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  2. S3Alex
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    S3Alex Rarely neutral

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    You've already tried the easiest and most likely suspects,and you don't need anything other than stock plugs,even at the sort of power my car runs.

    Does the car have a proper CAI?....sometimes at Stg2+,airflow can be limited by the stock induction system,and will result in misfires.

    Other than that,the best route is to have the car logged by a decent tuner,on the road,under load,and see exactly what it's doing.
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  3. ninjakid
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    ninjakid Member

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    I would check to see if you have the RS4 fuel valve, as with the standard one I understand there can be issues at around the 5k rpm mark. Mine is standard and after being remapped, the power curve is showing a flat spot at those revs. I maybe wrong but check it out.
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  4. Poma7
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    Poma7 New Member

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    Thanks for the fast replys, yes it has an itg CIA and it's heat wrapped, it's is also fitted with the rs4 fuel valve. I'm just thinking it's a plug issue as it's strange how it reacts differently with different plugs in, do you have the manufacturer and part number for oem plugs as my local motor spares gave me ngk platinum as oem plugs and it doesn't boost at all with those in! With the iridium ngk Ix in its a little bit better but still misses like mad even at 3k rpm. It boosts fine upto 5k rpm with the denso racing plugs in... Strange...
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  5. DJ-S3
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    DJ-S3 Member

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    What ninjakid said. RS4 fuel valve should sort that.
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  6. Poma7
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    Poma7 New Member

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    Do you think I need a new rs4 fuel valve then? Any ideas why it runs different with the different spark plugs too chaps? Thanks
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  7. S3Alex
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    S3Alex Rarely neutral

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    At Stg2+ the RS4 valve is a luxury rather than a neccessity but yours has one in any case.

    What you need to do is to have the car logged under the conditions that make it misfire to find out what is happening.
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  8. swatchuk
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    swatchuk Member

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    I had this issue with my s3 when I first got it. I did all the same obvious things that you have done. Even tried the maf sensor. It is the plugs that are causing the misfire as they are so sooted up but the cause is not enough air getting in. There are flaps in the inlet manifold which stick and need 're-aligning and cleaning to allow better airflow. Put new plugs in after that and it's been fine ever since.
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  9. Poma7
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    Poma7 New Member

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    Thanks again for replys, that sounds possible, is there a how to, for aligning? I have a vagcom, but am new to vagcom only really used it for scanning so far :) will have a look at removing inlet manifold when I get chance
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  10. essIII
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    essIII Active Member

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    Mate, before doing any more mechanical stuff, take Alex's advice and get the car logged while misfiring (i.e. out on the road, under load). Without that, you could end up trying another 10 things that don't solve the issue. Logging should highlight where the problem actually lies.
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  11. S3Alex
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    S3Alex Rarely neutral

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    If you're not totally familiar with the car,that will end you up with a lot of work,and a bag of parts.

    I'm not going to advise it again after saying one more time......get it logged by someone who knows what they're doing.
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