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S3 running lean after CAI... Code P0171

Discussion in 'A3/S3/Sportback (8P Chassis)' started by AdamSansom, May 11, 2013.

  1. AdamSansom
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    AdamSansom New Member

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    Hi,
    I've just fitted a CAI to my s3, ran a dtc check today and it's given P0171 which is fuel trim: too lean.

    According to ross tech, common cause is intake leak obviously meaning lots more air getting in which sounds right with the new CAI.

    Has anyone else had similar issues? I'm hoping to go to stage 2+ before long, but for now running stage 1 bluefin.

    So mapping will probably sort it out in the future, but for now..

    Whats your thoughts? I'm guessing my economy will be affected but other than that it shouldn't cause any damage?

    And will the ECU adapt the trims over time to accommodate?


    Any help much appreciated,
    cheers
    Adam
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  2. coreythorny
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    coreythorny Member

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    Running lean is really not clever at all!
    your fuel does many things, one being cooling the piston. Less fuel means less cooling which can cause catastrophic damage.
    However, it could be just a case of a bit better economy.

    Really worth sorting and trying to avoid spirited driving in the mean time. Better safe than sorry.
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  3. AdamSansom
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    AdamSansom New Member

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    Thanks! I had wondered, haven't driven spiritedly since the light came on.

    What do you think is the best thing to do?

    I don't know why this hasn't happened to everyone with a CAI, admittedly I have made my CAI but have made the maf section the same cross sectional area, and used the itg g60 filter. So it's very much exactly the same as the itg unit.

    Does anyone on here run the itg or any other CAI with stage one mapping?

    Cheers
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  4. coreythorny
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    coreythorny Member

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    I'm running a ITG on standard map no issues.

    It might be worth taking it somewhere who specialise in these engines or have more of a understanding?
    im sure someone on here might know and be able to help though.
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  5. S3Alex
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    S3Alex Rarely neutral

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    I'm currently using an ITG on Stg4 mapping with no issues.......small differences in the intakes can make big differences in airflow,and you need to get someone who knows what he's doing to take a look at whats going on.
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  6. AdamSansom
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    AdamSansom New Member

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    Yeah, Stage 2 and over seems fine, that's what makes me wonder if the mapping isnt right for the intake, maybe the fuel trims are going out of range because it can't adjust far enough to compensate for the increase in airflow.

    Ill have to find somone who can do some logs to see what's happening.

    Can anyone recommend the best place around shropshire/west mids?

    Thanks for the help so far
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  7. 37
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    37 Member

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    Are you 100% certain that it affects the engine? If it were a cooling problem, wouldn't it show on the temp guage?

    I've got this problem with one of the Sensors which is giving this error and I was told it will only really affect fuel economy and thats it. This info comes from a very reputable garage of NW London.

    P.S I was told that the sensor is around £174.
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  8. coreythorny
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    coreythorny Member

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    Yes mate, running too rich can be just as bad oil. Same as the too little/too much oil debate.

    Worth a read: What Are the Dangers of Running Lean? | eHow.co.uk

    im not saying your car will go bang or that it won't. It's a combination of so many things which the above does partially cover. It's definately worth looking into though. Easiest way is monitor your AFR to see what it's running at. If the AFR is ok it would favour the idea of a faulty sensor.
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  9. 37
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    37 Member

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    Thanks. Sorry to OP for hijacking the thread but; how can I monitor AFR? The Garage did say it was a faulty sensor but I didn't go ahead with the change since I thought it was expensive since I purcahsed the car 2 days back then. Is there anything else I can spot? I've a 1.6 Sportback and managed about 225miles (London) in half a tank. Does that indicate anything? :unsure:

    One more thing I recalled - the report from OBD does say System Too Lean - Intermittent. Perhaps that is why the garage didn't insist on changing it??
    Last edited: May 12, 2013
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  10. S3Alex
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    S3Alex Rarely neutral

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    Exactly as corey says....

    Running lean,especially under boost,is potentially an engine killer.

    High EGTs are bad for the turbo,and high cylinder temps can result in piston damage.
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  11. 37
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    37 Member

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    Could someone confirm which part # /sensor do I need so that I can try and find it myself, perhaps a bit cheaper?!
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  12. JPK
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    JPK Member

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    There is a 40 page thread on vwvortex about fuel trim issues with aftermarket intakes. I would be VERY careful before running homemade intakes, no matter how skilled you are. Forge stuffed it up with their 'Wintake' and they do a lot of r&d.

    VWVortex.com - Aftermarket Intakes and Fuel Trim Issues
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  13. Lewis583
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    Lewis583 Active Member

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    There are quite a few sensors on the engine that affect the air/fuel ratio. So without knowing which sensor they said was the issue, no.
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  14. S3Alex
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    S3Alex Rarely neutral

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    It's not worth trying to save money on what could be an expensive problem.

    As above there are many areas where problems can arise and if large companies can still have issues with fuel trims then you have fewer options.
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  15. 37
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    37 Member

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    Thanks for replies chaps. I must add that I've a normal Sportback without any mods at all. Chaps at AudiVWSpecialist didn't insist on changing and only recommended the change since it will affect the fuel economy. I haven't got any lights on the speedo either. It was some Lambda sensor (can't recall :banghead:). Googling online, a lot of people have had the vaccum issue. How can I go about testing the vaccum :S
    Last edited: May 13, 2013
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  16. AdamSansom
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    AdamSansom New Member

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    The vwvortex thread is a good read!

    I think I need to get some logs sharp ish to see what's happening.

    Does anyone know who's closest to Shropshire with VCDS?
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