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Oh noes... Manual Boost Controller.

Discussion in 'A3/S3 Forum (8L Chassis)' started by Mings, Oct 21, 2009.

  1. Mings
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    Mings A3 1.8T Sport

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    [Oct 21, 2009]
    Hi Everyone,

    Just looking for a little help and advice if you'd be so kind!
    I've been having a poke around under the bonnet of my 1.8t AGU and have seen that the plonker who owned the car before me has fitted a manual boost controller, I've done a search on the forums and found that this is a bit of a bad idea for various reasons.

    I'm just wondering what the mbc will have replaced? Is it the n75? If so where is the best place to get one from and which 'letter' should I get as I hear there are loads of different n75's.

    Look forward to hearing your thoughts.
    Last edited: Oct 21, 2009
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  2. badger5
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    badger5 www.badger5.co.uk Site Sponsor

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    [Oct 21, 2009]
    mbc does replace the n75 yes.. do you have any check lights on the dash? chances are hopefully its electrically plugged in somewhere but not connected vac pipe.

    get the std valve for your model is my advise. later J valves can spike, which may or may not be what you want
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  3. Mings
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    Mings A3 1.8T Sport

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    [Oct 21, 2009]
    Thank you for the response, Bill.
    I don't have any lights on the dash and the car seems fine but I heard there is a chance it will damage my engine to have this fitted in the long run.

    Would the best place to get this from be an Audi dealership? If so could someone please provide a part number?

    Also, I have heard about the n75j, I am not really interested in increasing the performance, I just don't want to do any damage to my beautiful, beautiful car. Does anyone know which letter/revision n75 should go on an AGU engine?

    Thanks all :)
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  4. badger5
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    badger5 www.badger5.co.uk Site Sponsor

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    [Oct 21, 2009]
    so long as its not running excessive boost over std (without the fueling and ign timing to go with it) it could well be fine.

    do you know what boost it runs? 7psi ish is about std level, remapped is double this
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  5. Mings
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    Mings A3 1.8T Sport

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    [Oct 21, 2009]
    I don't have a boost guage and the controller itself is pretty non-descript, counter-clockwise for less boost, clockwise for more boost supposedly.

    What symptoms or problems could I expect to encounter if there was too much boost?
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  6. Westy
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    Westy Double Dark Side! Diesel & 8P

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    [Oct 21, 2009]
    I would have thought that your car would go into limp mode if you were pushing too much boost by a non electrical valve. You'd get a dash light come up and your car wouldn't run properly.
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  7. Mings
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    Mings A3 1.8T Sport

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    [Oct 21, 2009]
    So there's no risk of me damaging the car with the boost controller set how it is now then? (It's been at the same level since I got it in January and I've not once seen a dash light come on (cept handbrake, petrol and lights :p ))

    Thanks for the advice so far, good for the ol' peace of mind :)
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  8. Westy
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    Westy Double Dark Side! Diesel & 8P

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    [Oct 21, 2009]
    The ECU should intervene if it thinks the boost is too high and will protect you engine by putting your car into limp mode. You have nothing to worry about mate.
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  9. badger5
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    badger5 www.badger5.co.uk Site Sponsor

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    [Oct 21, 2009]
    Westle: presuming the non map sensor equipped car even has a clue what boost its running??

    AGU is'nt it? (correct me if not please)

    more boost without the fueling to go with it is risking lean running, which is melted pistons and burnt valves
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  10. ash_pearce
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    ash_pearce Member VCDS Map User

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    [Oct 22, 2009]
    I run a 'J' valve on mine with no issues. No increase in boost pressure just seems to hold it longer. I've done lots of vagcom readings to check fueling all's ok for now...

    To be honest though i'd ran out of cash after my rebuild and the j valve was loads cheaper otherwise i would have stuck with the standard n75.
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  11. Mings
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    Mings A3 1.8T Sport

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    [Oct 22, 2009]
    I think I'm going to grab myself an N75 just to be safe. I'm pretty sure my engine is AGU but I'll check again tonight just to be sure.

    I'm presuming the best place to get an N75 is the Audi garage? How much do they generally cost and does anyone have the part number please?!

    Thanks for all the help and advice so far!
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  12. jonny87
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    jonny87 Active Member

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    [Oct 22, 2009]
    just to muscle in on this topic, the problems that can occur through having a mbc fitted described by westle, sound exactly like the problem im having with my bt s3 (epc light comes on and in limp mode) and i have an mbc fitted, ive checked and its still connected electrically

    should i swap the mbc out for an n75 valve of some description?

    i need to find out what engine i have exactly, where can i find the engine code? (now ive asked its gonna be somewhere really obvious lol)
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  13. Andrew@A.L.D
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    Andrew@A.L.D May add NOS to 600+bhp?

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    [Oct 22, 2009]
    I also have a MBC fitted with the N75J still connected with no lights and seams to run fine.

    Running 15psi on a S3
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  14. badger5
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    badger5 www.badger5.co.uk Site Sponsor

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    [Oct 22, 2009]
    boost deviation code thrown?
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  15. jonny87
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    jonny87 Active Member

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    [Oct 23, 2009]
    ok guys ive taken some pics of the setup on my car, as i got nothing to compare it to hopefully someone will be bale to shed some light on the situation, so here we go:
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]

    also i just checked my engine code its an auy, dunno if this is helpful or not lol
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  16. s3dave
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    s3dave TFSI Hybrid Supporter

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    [Dec 15, 2009]
    it looks to me like you have your n75 valve still there, and for some reason they have put a mbc in too for good measure (n75 is the second pic) so you need a straight piece to replace the mbc and join the pipes together
    hth dave
    #16

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