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Agu boost pressure and problems please read.

Discussion in 'A3/S3 Forum (8L Chassis)' started by ash_pearce, Apr 16, 2009.

  1. ash_pearce
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    ash_pearce Member VCDS Map User

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    [Apr 16, 2009]
    Right before anyone says other wise I have done a search but cant find the answers..

    I'm still running my engine in but have been gradually applying more throttle as the miles clock up. The other day I was only getting 0.5 to 0.6 max boost with the occasional rise to 0.9 which gave an overboost fault in vagcom. The other issue was a major fluttering type sound

    vagcom'd again and it gave me
    01262 - Solenoid Valve for Boost Pressure Control (N75)

    26-00 - Output Open

    Checked wiring all fine, so replaced the n75 with a new j valve today, both problems still there,

    checked dv and found it was leaking (sucked on the small vacumn pipe no pressure) Bought a new bailey recirc type from local shop this evening still only boost to 0.6 bar but the fluttering noise is there but not as loud.


    Sorry for the essay but any ideas?

    What pressure should my agu boost too?
    Why do I have a silly escort sounding audi(fluttering)

    and .. I've checked all the hoses no leaks.

    thanks in adavnce
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  3. ash_pearce
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    ash_pearce Member VCDS Map User

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    [Apr 17, 2009]
    spent the last 2 hours googling and it seems that 0.6 bar is the standard pressure.

    Still not sure why I can hear the flutter noise though? are the bailey valves any good?
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  4. HTC
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    HTC Active Member

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    [Apr 17, 2009]
    Is the DV actually opening? I know you say you've checked the pipes but is the DV vacuum pipe to the bottom of the inlet manifold okay? A flutter might suggest boost dumping back through the compressor.

    AGU should only boost to about the levels you are seeing. 0.9 is too high for standard. I'd refit the original N75 as the J opens the wastegate later and thus the over boost.

    Try disconnecting the electrical plug from the N75. You'll get another code to clear but you'll then run off wastegate mechanical spring pressure which might help to diagnose the fault.
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  5. ash_pearce
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    ash_pearce Member VCDS Map User

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    [Apr 17, 2009]
    Replaced all the vacuum hoses yesterday just to eliminate them. I've tee'd this to the boost gauge though - correct?

    The overboost occured on the stanard n75, I went with the j valve as it was cheaper and a remap is on the cards soon as its run in and have read they are supposed to help smooth the boost out on a mapped agu.

    I'll unplug the n75 tomorrow and try what you suggested, thanks for your help.
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  6. HTC
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    HTC Active Member

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    [Apr 17, 2009]
    Teeing into the DV feed is correct for a boost gauge on the AGU. So it only flutters when you get off the gas, right? Not during boost.
    Is the DV piston moving okay, standard spring? Usually fluttering is ripped diaphram (not in your case) or pressure back through the turbo........hmmm, strange one.

    If you go for a generic remap you still might have problems with the J valve as it would have been coded with the standard valve in mind, though people do have success with them. See how you go. Overboost will deffo be down to the extra pressure via the J valve with the stock map.
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  7. ash_pearce
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    ash_pearce Member VCDS Map User

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    [Apr 17, 2009]
    Almost sorted... tried lots of combinations today, n75 on n75 off, wastegate conected and not, dv on dv off etc..

    Decided to make a pressure tester out of a tyre compressor, plumbed it all together and it would only hold 0.3 bar, found a very small leak on an injector o ring seal, replaced that and it held 0.5 bar but no more, couldn't find any other leaks.

    Replaced all jubilee clips still no more than 0.5 bar though.

    Had a look at the new bailey re cir dv, the piston moves freely, tried mounting it the other way up, no difference. On the plus side the flutter noise seems to have gone, just a whoosh sound when the recirc opens.

    Out on the road it feels better up to 3.5 to 4k revs when things slow down, it gets up to these revs and then takes a long time to go any further. The boost drops off after 4k is that normal?

    Been on google and found an intersting thing about fuel pressure, going to check that next although i have my doubts.

    http://www.ilexa.co.uk/forum/index.php?topic=18580.0

    thanks for your help HTC.
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  8. HTC
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    HTC Active Member

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    [Apr 18, 2009]
    0.5 bar or about 7psi is about normal for an unchipped AGU I believe.

    The k03 does run out of puff in the higher revs. Did a quick search for a standard 1.8T dyno. Torque drops off as you can see (don't know if this is an AGU engined car)

    [​IMG]

    I would also log the MAF g/s value. You should be seening about 120g/s max for a 150bhp car.

    Here's how to test fuel pressure. The correct way to test is via fuel delivery rate and system pressure as follows.

    Fuel Delivery Rate:

    * Remove number 28 fuse.
    * Make up wire that has a switch in it.
    * Connect one end of the wire to the contact at the fuse box where you removed the fuse.
    * Connect the other end to the battery +12v terminal (don't switch on yet)
    * Remove the fuel delivery pipe and put it into a measuring jug. Pipe No.2 in the diagram.
    [​IMG]
    * Attach a voltmeter across the terminals of the battery.
    * Turn on the switch in the lead to run the pump. Run it for 15 seconds and remember the voltage reading whilst its running.
    * Compare the amount of fuel delivered with this diagram. It's a graph of minimum delivery Vs voltage. Voltage can be a couple of volts lower than when the car is running. This is okay.
    [​IMG]


    System Pressure and holding test:

    * Connect a pressure gauge with cut off valve inline within the fuel delivery pipe
    [​IMG]
    * Run the engine. Pressure gauge should read 2.5bar
    * Disconnet the vacuum pipe from the fuel pressure regulator. The pressure should rise to 3bar.
    * Turn engine off and watch the gauge. After 10 minutes the gauge should still read a mimimum of 1.5bar.
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  9. ash_pearce
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    ash_pearce Member VCDS Map User

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    [Apr 19, 2009]
    Fixed!

    Checked the fuel pressure, slowly rose to 2.5 bar then to 3.0 with vac removed.

    Changed the fuel filter and bang straight up to 2.5 on start up. the system holds 2.5 bar for 20 mins at which point i was bored.

    Out on the road the car is alive at last, revs up smooth and holds the boost for longer now.

    Saw a max of 126.94 g/s at 6400 rpm on the maf readings and the n75j is causing no probs only showing 46% duty cycle.

    Thanks for your help, going to get some more miles done then probably take it to jabba as there fairly close to me.
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  10. HTC
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    HTC Active Member

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    [Apr 19, 2009]
    Glad it's sorted. I had to fit a new filter when my car was last mapped which was causing low fuel pressure. VAG don't have a service schedule for the filter, but IMO everyone should change them from time to time.
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