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does this sound like a n75 problem ?

Discussion in 'A3/S3 Forum (8L Chassis)' started by kewe, Feb 24, 2014.

  1. kewe
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    kewe New Member

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    been off for a while trying to get the car up to scratch with bits and bobs, just had a new turbo and fuel,oil and filter, injector and fuel line cleaner ect, fitted a boost gauge as well to try and diagnose this.
    basically my problem is on the motorway at 4th and 5th around 3500 rpm the car losses boost and will hit limp mode, holding 10 psi of boost, dont really have allot of money to throw on map sensor maf and n75 so kinda need to get a second opinion, when i accelerate in 2nd gear form low rpm the turbo will kick in quite hard, sometimes to 28psi off boost and then drop down to about 18psi, will have no limp mode, on the motorway if im in 5th and i give it a bit of go it will spike till abut 23-24 and then drop to 19-20 and hold the boost, next minute it will hit limp mode and cut the boost. im planning on intalling a 3 bar map snesor to go with a chip, because to my knowledge the cars not been mapped, alough im thinking spiking at 2 bar is a bit high for not being chipped iv tried to log maf and map sensors with vcds if this is any help, sadly these are in 2nd or 3rd when it doesnt hit limp mode
    map sensor map.jpg maf sensor maf.jpg
    any help is appreciated in advanced,
    kieran
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  2. superkarl
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    superkarl MAN OF STEEL

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    That boost is ridiculous! If you like your car/engine DO NOT take it anywhere near 2bar.

    Its going into limp because of the overboost. Log it on vagcom and get codes.

    Check your n75 is plugged in, correctly orientated and all pipes to and from are boost tight.
    a smoke test would reveal everything tbh, that should be a priority
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  3. schwartza3
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    schwartza3 Member

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    had a similar issue, found I had a tear in the line from N75 to wastegate.
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  4. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    What you have there is uncontrolled boost... you also cant just fit a 3bar map sensor as the map will have no idea it's there plus 2.5bar is a hard coded limit in the software. ..

    Have you tried unplugging the n75 electrically and see what boost you get?... wild boost like that is down to a fault in boost control hardware if you believe your car is not mapped...

    log block 115 to see what requested boost is... std boost is around 0.8bar so request will be around 1800mb peak

    <tuffty/>
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  5. kewe
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    kewe New Member

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    Il try disconnecting the n75 tonight, vac pipes are all renewe and il try and get a vagcom scope of when it cuts the boost with requested and actual, thanks again
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  6. S3 Paul
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    S3 Paul Active Member Staff Member Regional Rep

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    My car will spike to 23/24 psi some times ( if i try and make it do it ) but is mapped so maybe mine is just a bad map relying on boost alone to make power?
    I would as said remove the N75 plug and see what it makes then.
    Then if you can double check all the pipes are correctly connected ( i nearly plumbed my N75 in wrong) so i know its possible.
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  7. kewe
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    kewe New Member

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    done a quick motorway run to force it into limp mode, the faults came up with

    01282 - intake manifold change over valve n239 open circuit intermittent
    00575 - intake manifold pressure 17-10 controll difference intermittent
    01237 - fuel shut off n109 04-00 - mechanical malfunction

    10282 i have the solinoid unplugged when i done the egr delete
    10237 fuel shut off, i was cleaning the quantity adjuster and think when i took it off this may have flasgged up, cleared first time not came back

    00575 i think this is my problem, woudnt clear until i done the ignition flick then it stayed off for a minuiit, then flagged back up

    thanks again
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  8. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    Ok... would have helped letting us know this was a tdi!!

    Over boost issues on tdi's are usually down to sticky VNT... as you say you have had a new turbo then I don't know... I assume it was an actual new one or was it a 'new to you' secondhand one?

    <tuffty/>
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  9. kewe
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    kewe New Member

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    sorry mate thought it came up at the side, no it was a brand new core done in my works turbo unit all spun up and balanced, had a quick read there about the problem i can confirm its not a cat blocking anyway, going to do a run with logging block 11, boost actual and requested to see if it can reveal anything,
    kieran
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  10. kewe
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    kewe New Member

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    Just have it a blast there, the n75 is sittin round 94% constantly and the boost actual is allot higher than requested, when I disconnect the n75 the car is constantly flat and doesn't boost, this leaves me to suspect either the actuator has been tuned up when the turbo was done or when ov turned the fuel pump up it has also turned up the boost to compensate, but an ex VW mechanic told me the ecu woudny do that, any thoughts and opinions are welcome as always but I'm thinkin turn te fuel pump back down and if that doesn't cure it it's going to be the actuator has been adjusted and that's what throwing up the 00575 problem ?,
    Thanks again, Kieran
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  11. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    If the actuator had been played with you would have loads of boost with the N75 disconnected... it won't actually request boost if the N75 is disconnected but it will still make boost as the actuator will have a set crack pressure..

    You will need a boost gauge of some description to determine boost..

    I don't know much about diesels so can't comment on the fuel pump... I would advise however that you set the fuel pump pressure back to factory settings...

    Should also say that diesels run a lot of boost as std anyway... on all the diesels I have seen Bill tune he has never touched the engine in any way... I know that one of the things you do to diesels to get more power is add fuel but thats done through mapping rather than cranking up hardware

    TDi's have a 3bar map sensor as std IIRC...

    The 00575 code resolves as:
    00575 - Ross-Tech Wiki

    The boost deviation you are suggesting you have is probably why this has popped up

    <tuffty/>
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  12. kewe
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    kewe New Member

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    Cheers tuffy, al be checking the map sensor but I thought they were 2.5, will be turning the fuel pump down and re adapting values boost was about 25 psi when it peaks but il post updates as I go
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