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1.8T AGU Boost or ECU problem

2dutch Jul 30, 2020

  1. 2dutch

    2dutch Registered User

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    Hello,

    (please excuse any spelling or grammer mistakes as English isn't my first language)

    I've been batteling a weird boost problem on my Audi A3 with AGU engine. Ive been trying to figure it out for some time and have posted on a dutch forum but can't get to the root of the problem yet.
    The engine is stock except for a remap. The car runs, starts and drives absolutely fine, no issues at all except for the sudden loss of about 40hp. My max boost pressure dropped from 20psi to a constant 11psi. where I used to get a lot of power at around 2500rpm it is now completely flat. It just holds at 11psi. At 11 psi N75 is triggered to open the wastegate and hold it as I tried it without the actuator line and it is able to make more than decent boost.
    Has my ECU lost it's tune??

    What i've done untill now:
    - vagcom: no fault codes
    - pressure tested hoses (holds pressure no leaks.)
    - Replaced N75
    - Replaced Diverter valve
    - Replaced throttle housing
    - checked pcv system for leakes and replaced valve, hockeypuck seems fine
    - If I take of the acurator hose to the N75 and (carfully) test it, it boosts without problems to 20+ psi
    - If I disconnect N75 Boost droppes to 6psi
    - Disconnecting MAF makes car slower

    What else is there to check? Has anyone ever had a busted MAF while the car is running fine except for power loss? Has anyone ever had an ECU that lost it's tune?

    Thanks in advance. I hope this forum is able to help me with this problem
     
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  3. <tuffty/>

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

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    Your ECU won't have lost its tune unless you have over written the map with another one...

    Not had a lot to do with M3.8 ecu's but they are massively reliant on the MAF sensor which is prone to fail...

    Ideally it would be an idea to log the car to see what the ECU thinks is going on and work it back from there

    <tuffty/>
     
  4. 2dutch

    2dutch Registered User

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    Have you ever come across a MAF that acts like this? Running just fine except for the power loss?
    I read a lot about faulty MAF sensors and idle problems etc.

    I have a neighbour who has a program that can log the car while driving I think
     
  5. <tuffty/>

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

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    VCDS will log the car... faulty MAF sensor can still allow the engine to drive well enough on light loads but tend to show issues when you put your foot down

    <tuffty/>
     
  6. 2dutch

    2dutch Registered User

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    Does anyone know if the AGU engine throws a code for a defective G40 Hall sensor??
    I've read that the controll unit lowers boost and timing if it gets no signal
     
  7. 2dutch

    2dutch Registered User

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    Tried an other MAF today, no change. Does anyonte know about the G40 camshaft position sensor throwing a code?
     
  8. Erikn89nl

    Erikn89nl Registered User

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    Not sure about camshaft code, but I've had one for the crankshaft pos sensor (G28) so I'd assume they were the same. Mine is also an AGU (for now). Whereabouts in NL are you?
     
  9. 2dutch

    2dutch Registered User

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    I can't find the G40 sensor in the VCDS reader aswell. Should be in block 4 but there is nothing there.
    If I take the plug of the sensor and run it nothing much changes. Maybe a bit less boost on the guage but nothing spectacular.
    Also no difference in starting or idling with the sensor unplugged.
    So I guess I'll check the power feed and change the sensor.

    I'm In Enkhuizen
     
  10. 2dutch

    2dutch Registered User

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    Changed the camshaft position sensor aswell, no result.
    - I have no rpm reading on the tacho while starting, Once it starts I get rpm reading. Anyone know if the agu should have like 300rpm signaling during start up?

    For now i'm running manual boost controll to get my boost up.
     
  11. 2dutch

    2dutch Registered User

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    I stillgot this problem. I'm running a manual boost controller now, this fixes the low boost issues but I would still like to find the problem.
    Is there anyone who can answer this one?
    - I have no rpm reading on the tacho while starting, Once it starts I get rpm reading. Anyone know if the agu should have like 300rpm signaling during start up?

    Any other ideas?
     

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