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N75 valve help

Discussion in 'A3/S3 Forum (8L Chassis)' started by brys3, Jul 2, 2010.

  1. brys3

    brys3 Member

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    Hi, I'm going to change my n75 valve based on the fact my engine isn't supplying the boost the map is asking for. Now I've read a little into different part numbers for different outcomes. Is it best to stick to the part numer ending in f or something else? Anywhere online I can get one from?
     
  2. <tuffty/>

    <tuffty/> Badger 5 Edition...Its all about the flow...
    Staff Member Moderator

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    Are you sure its the N75?

    I wouldn't replace it with anything other than the 'F' variant as you may well keep hitting limp mode

    <tuffty/>
     
  3. brys3

    brys3 Member

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    No I'm not sure, that's what the guy with vagcom said to try first as it wasn't boosting at what the ecu required. No faults where found and i don't know whether this ties into my other thread of having no power
     
  4. <tuffty/>

    <tuffty/> Badger 5 Edition...Its all about the flow...
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    hummmm... the poor N75 always seems to get the finger pointed at it when there is no boost lol...

    I would be checking for leaks first tbh... the N75 is £40 to £50 to replace IIRC, lot of money if its not that.... know anyone near you with 1.8t engine VAG that you can do a test swap to see if it makes any difference?

    What blocks did you log and do you have the logs available to post up?

    There are other reasons for lack of boost... on older K03 turbo'd cars its common for the turbo to be the issue but not personally seen it with S3's and K04's as yet....

    Could be something as simple as a split pipe...

    <tuffty/>
     
  5. brys3

    brys3 Member

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    Ok so what hoses should I be looking at? I'll ask him and see what he says about blocks and if he can email me what he got. It's an 01 btw so what turbo will it have. Thanks very much for the advice
     
  6. Nixa

    Nixa New Member

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    Hmm this is interesting, my AMK S3 (chipped) has a N75H on it... I'm assuming it didn't come there from the factory by what I've been reading here. Anyway, just to add a little insight into the difference between the H and F, I'm seeing about 2-3psi difference at peak overboost - but take into account that's 25 psi on the F and 28 psi on the H (Yes I know, and hence why I found this forum :) )
     
  7. Welly

    Welly VX220 SC Driver :)

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    WOW, 28 PSI?

    That turbo will eat itself very quickly at that boost...

    100% a problem there!
     
  8. Nixa

    Nixa New Member

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    Yeah, not sure why yet, figure somethings not controlling something right.
     
  9. Welly

    Welly VX220 SC Driver :)

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    Hmmmm, that sort of boost would make me think an actuator problem straight away. Possible a split in the pipe down to the actuator from the N75 valve.
     
  10. Chlippo

    Chlippo Member

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    F are the ones S3 got from factory?

    other thoughts...get the N75 you like and get an mbc, so no more boost spikes, but at this point i beleive all the N75 would be equal, since the mbc have the control over maximum boost...anyways the question:
    With an mbc installed, would it matter what N75 code you got (J, F, H, C)?
     
  11. Welly

    Welly VX220 SC Driver :)

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    Not really, no, as the MBC would eliminate the boost spike as you said.

    The C and F tend to produce a more progressive power curve though, so if installing and MBC also, then a C or F would be the better choice IMO.
     
  12. brys3

    brys3 Member

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    So why do you have j?
     
  13. Nixa

    Nixa New Member

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    I think my problem is tune related, it's asking for more specified boost than the MAP can read and hence not opening the wastegate fully.
    As for this topic regarding the n75, whatever your car comes with factory if you plan on chipping/tuning without any mods, or running parallel MBC... H/J if you want a lil more from factory.

    Just my 2C
     
  14. Welly

    Welly VX220 SC Driver :)

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    Because I don't have an MBC installed as well....

    As I said above "so if installing an MBC also, then a C or F would be the better choice IMO".
     
  15. Welly

    Welly VX220 SC Driver :)

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    OK, I'm not sure what you're getting at here to be honest.

    However, for your ECU to be providing more Actual Boost that the MAP Sensor can read, the boost level will have to be 22.48 PSI (or 1.55 BAR) or more.... And that is a lot.

    What map are you using?
     
  16. little_lockyer

    little_lockyer Lockyer89

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    May i ask what an MBC is?! Just reading through this and trying to understand it all, as i have a problem that may be related to this, i have the n75(solanoid valve yes? this is what the haynes manual sasys!!) in my hands now, and mine reads F, i have an aum 1.8t, and my car boosts well when it does, but other times it just doesn't boost at all!! Nothing comes up on vagcom. Also just checking the coil packs, if they are bosche, is this clearly stated!?
     
  17. brys3

    brys3 Member

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    Well mine is remapped, not a good map however. Vagcom says it asks for 1.3 bar but only delivers 1.1 I'm going to bypass the n249 valve so is it best just to go for the standard s3 n75?
     
  18. little_lockyer

    little_lockyer Lockyer89

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    Is the n249 valve the one closest to the dipstick?
     
  19. Nixa

    Nixa New Member

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    the n249 sits ontop of the crankcase (if you own a s3 under that plastic cover on top of the engine). It has several pipes going in and out, of which one leads to the top of the DV. In essence the n249 is a method for controlling DV operation by allowing vacuum to reach it even under boost opening the DV and releasing boost (via the vacuum reservoir which is that black boxy part next to the n75).

    If your mapped it I would personally say keep your standard n75, it works just fine and gives a more linear drivable boost delivery anyhow.

    @Welly - it's asking for 1.55 bar, MAP can deliver 1.54 or 2540 mbar, standard MAP. Only 10 mbar but might be enough, either way I wasn't happy so they're making me a map at 1.4 bar. To be honest I don't know the person doing my tune as he's in the UK and I'm on the other side of the world, but the fact he ramped up the boost to that level is a little worrying.

    Also have you tried a MBC in parallel and what type, I'm just wondering your opinion on what would be better - bleeder or S&B

    @lockyer - The fact your car is 'sometimes boosting' most likely isn't coil related. If you have a registered vagcom run some logs on group 115 (specified boost vs actual boost) and post them here. Also group 032 and a group with "n75 duty cycle" (114?) if you have time. Do not run both at once because the sample rate will be too low.

    If you want a few things to check: the wastegate might be sticking, the n249 or n75 may be malfunctioning, some form of mechanical limp mode (should throw code though). Possibilities are hard to guess.
     
    #19 Nixa, Jul 15, 2010
    Last edited: Jul 16, 2010

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