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Boost issues on S3

Discussion in 'A3/S3 Forum (8L Chassis)' started by Billgo, Apr 13, 2013.

  1. Billgo
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    Billgo New Member

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    [Apr 13, 2013]
    Hi Gents, I'm new to this forum and have only just returned to VAG ownership after 5 years or so.

    Basically I have recently bought a 2001 Audi S3, it was advertised with approx 300bhp and a hybrid turbo, the guy I bought it from didn't know much about it but it pulls well, everything seemed in order and he had a lot of receipts including one for the turbo from CR turbos for the hybrid and extensive work from a company called Quick Motorsport.

    So as I said everything is running well boosting to 1.5 bar and still holding 1.0 - 1.1 bar at the redline but thought I would check everything over and today was the first chance I had to have a good poke around under the bonnet....

    First thing I noticed is it has a turbo tip fitted and the tube that the N75 valve is supposed to be connected to has a bung in it and the N75 is just cable tied up. Second thing is that the N75 has manual boost controller type thing attached to it (only the bottom of the three connections was connected on the MBC so can't believe it was actually doing anything)

    So I thought I would remove the MBC and install the N75 on to the tip as it should be... I took it out for a drive and now the boost seems out of control (I was careful on the throttle and it quickly boosted beyond 1.6 - 1.7 bar so backed off immediately). I am now running it with the N75 disconnected which gives me 5psi as I'm now concerned I have no idea what map this thing is running and if its fuelling properly etc.

    Anyone got any ideas?? Is this a faulty N75 ..? What would be the correct way to install a MBC and do most people just use purely the standard N75 boost control ?
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  3. Westy
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    Westy Double Dark Side! Diesel & 8P

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    [Apr 13, 2013]
    A lot of people with hybrids have to run an MBC alongside the N75 to cap boost spiked from the turbo surging. Check the N75 hoses are all on the right way as that can give you issues. I can't remember the order off my head but I'm sure someone will be along who does know.

    You're doing the right thing by running it on actuator pressure only. If I was you id keep it that way till you've had it checked on a dyno for fueling.
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  4. Billgo
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    Billgo New Member

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    [Apr 13, 2013]
    Thanks for the reply, I checked the N75 is connected correctly and it's all good.

    I read about using both the N75 and a MBC, however the way mine was plumbed in I couldn't see how it could possibly work.

    Below the actual MBC.... The pipe at the bottom was connected to the TIP side of the N75 (the longer leg) and that was it!! The bronze coloured bung was in the TIP.

    [​IMG]
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  5. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    [Apr 13, 2013]
    The boost being out of control is probably why the MBC was fitted... do you know who mapped it? (assuming of course it was mapped!)

    Fitting an MBC (or bleed valve in this case) is masking an issue... have fitted these to cars with spikey/pikey maps to curb boost spikes as an option to having a proper map...

    Do you know what injectors its running? 300hp requires larger injectors than the std S3 ones...

    Any chance you could grab a working copy of VCDS and do some logging? I worry when a 'mapping solution' includes a bleed valve...

    Check you have the N75 the correct way around... it should be a black valve not a brown valve (another pikey mod) too... longer outlet goes into the TIP, boost in the bottom and the opposite side to the long one to the actuator...

    <tuffty/>
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  6. Billgo
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    Billgo New Member

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    [Apr 13, 2013]
    I've no idea any of the details in terms of the upgrades.... As mentioned I've had the car a week or so and today was the first chance to poke about the bonnet.

    i agree it all seems a bit Micky mouse, hence why I've disconnected the N75 to just run 5psi to be safe.

    Any ideas how the boost would be being controlled with the setup I described earlier with the MBC connected to TIP side of the N75 with the other two sides of the MBC just open, as this isn't like the setups I've seen.

    I must get myself a new cable so can use VCDS, as I said I'd taken a break from VAG cars for the last five years or so
    Last edited: Apr 14, 2013
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  7. Westy
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    Westy Double Dark Side! Diesel & 8P

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    [Apr 14, 2013]
    Where abouts are you located? I'm sure one of the friendly ASN members on here with VCDS could lend a hand if you ask nicely.

    In the forums section there is a VCDS section and within that forum there is a map with all the VCDS owners that are willing to help out. Take a look.
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  8. Billgo
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    Billgo New Member

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    [Apr 14, 2013]
    i checked and its running injectors with a part number of 028 0156063 and a 3 bar regulator which seems to be standard, I've checked the N75 valve and its the black one and is correctly installed in terms of the long leg going into the TIP, every other connection has still got the original audi clips on so doubt has been changed.

    Next step is get a proper map, can anyone recommend somewhere good in Kent preferably ??
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  9. badger5
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    badger5 www.badger5.co.uk Site Sponsor

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    [Apr 14, 2013]
    std injectors.. ~386cc which typically max out duty cycle at 280bhp level.

    Overboosts on N75 because of the map... Common for some to use if they cant map properly me7 boost control
    MBC/Bleed valve fitted because of this.

    I would also be checking afr's are safe under this boost... If they cant manage boost control, perhaps fueling + rest of map is also questionable. Worth checking to be sure to be safe
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  10. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    [Apr 14, 2013]
    As Bill has said, these are std injectors so I very much doubt you are making the 300hp you think as these max out on a 3bar at just over 280 ish hp as a rule...

    I don't know anyone in Kent but Bill at Badger 5 is worth the trip and has loads of experience with this setup...

    <tuffty/>
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  11. Billgo
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    Billgo New Member

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    [Apr 18, 2013]
    Right I purchased a VCDS cable and registered a copy of the excellent VCDS lite. Tonight I reconnected the bleed valve and tweaked it back to 1.2 bar max on the boost gauge and went out and did some logging, what I found was basically the map is a micky mouse map by the looks of it !!

    First thing I did was the MAF, this looked really healthy if not a bit unbelievable peaking at just over 230 g/s

    [​IMG]

    So next I did requested vs actual boost, this to me looks like there was no attempt by the mapper to bring this in smoothly, just a simple 1.5 bar request straight away !! Remember this is with the boost pegged back with the bleed valve to 1.2 bar. It hits 1.2 bar at 3,200rpm does this seem normal ? The N75 duty was just 95% the whole time, which I guess is because requested boost is never hit ??

    Any ideas why this doesn't cause some kind of limp mode or fault code for underboost ??

    [​IMG]

    I thought it was then wise to check the A/F ratio since everything else seemed a bit cowboy with this car. Although this tapers off nicely it seems very rich at 0.75 (11:1) no wonder it seems to drink fuel !!

    [​IMG]

    Don't get me wrong this car is pretty quick and has proven itself against an R32 Golf and Astra VXR just tonight.

    I'm guessing that any of the reputable tuners could write a map over the top of this garbage and everything should be back to as it should be ??

    Anything else that would be a good idea to log ??
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