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N75 working correctly ??

Discussion in 'A3/S3 Forum (8L Chassis)' started by Essflee, Oct 28, 2010.

  1. Essflee
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    Essflee Active Member

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    Hey guys,

    I've just borrowed my mates liquid S3 gauge and after checking various things I came across the N75 valve,

    I just wanted to know what to expect as a reading when coming on boost etc, it has a reading based on opening 100%, through experimenting with it the most I seem to keep getting is 93%, is this ok or does it suggest my N75 valve isn't working correctly ??

    It's all well checking these things but in this case I don't know whether it's a good or bad thing...:shrug:

    Cheers
    Last edited: Oct 28, 2010
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  2. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    This is based on my understanding of how the N75 works so apologies if its not quite on the button...

    93% seems quite high, depends on what boost you are running etc...Map requests a target boost and ECU uses the N75 duty cycle to achieve it... higher duty cycles are usually indicative of high boost requests or that the ECU is having to use a higher duty cycle to meet the request relative to the actual boost it sees from the MAP sensor (or airflow from the MAF if no MAP sensor) which in turn could indicate a boost leak or other hardware related issue as to why it is having to work harder to achieve boost request...

    100% duty cycle is more or less the equiv of disconnecting the actuator and letting the turbo do its on thing.... 100% is normal on initial spool but having a higher number after that initial spool could indicate a problem... duty cycle will typically die down once the turbo has spooled initially... this does not necessarily mean there is a prob with the N75....

    <tuffty/>
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  3. Alex C
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    Alex C Well-Known Member

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    ok, a question of my own (N75 related). I understand the principle of the N75 but...

    When the ECU gives power to the solenoid in the N75 does this divert the charge pressure to the TIP or the actuator?

    And when the charge pressure is directed to the actuator does this help open the internal wastegate or keep it closed?

    thanks
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  4. bengal
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    bengal Member

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    Not sure if this is what your looking for but heres some info What the N75 valve does... - SEAT Cupra.net - SEAT Forum
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  5. Alex C
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    Alex C Well-Known Member

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    yep, thats what i have read before and understood it fine then, but had since forgotten. Cheers
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  6. bengal
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    bengal Member

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    No problem :thumbsup:
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  7. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    By default the N75 diverts boost pressure straight the actuator which of course means if the N75 fails for whatever reason you have the natural boost control pressure of the actuator and not boost that runs away and destroys your engine... the N75 works by bleeding boost pressure back into the TIP, the higher the duty cycle, the more air is diverted away from the actuator (thus creating more boost) and into the TIP (closed air system remember, this is the same as the way the DV valve works diverting 'metered' air back to the system).

    Simples :)

    <tuffty/>
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  8. Alex C
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    Alex C Well-Known Member

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    yeah simples :)

    Just forgot which way round it worked. But makes sense that it uses the `fail safe` method, cheers

    :salute:
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  9. Essflee
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    Essflee Active Member

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    Cheers Tuffty,

    I think the N75 shows 93% initially and the drops off from memory, I'm off to Jabbasport tomorrow so I'll see what he has to say,

    I think I could pick your brain about plenty of things on this liquid gauge to be fair...Lol
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