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vcds maf logs

Discussion in 'A4/A4 cabriolet/S4 forum(B6 chassis)' started by swarcup, Jun 4, 2013.

  1. swarcup
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    swarcup Well-Known Member

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    can anyone give me a few pointers to logging the maf, ive got a hex+usb+can cable borrowed from my brother in law, ive done a few bits like coding in cruise,dis auto locks so I thought i would log the maf to see what it was doing. i have gone into engine and advanced measuring and ticked the actual maf and spec maf and logged the readings. when i compare the two numbers they follow the same curve on a graph but actual is above the spec by between 200-300. have i logged the correct values, i did do a drive and was accelerating quite well and also some constant stuff.here is a copy of the results. if anyone has any info i would appreciate it
    chart.jpg
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  2. Audi Doodah
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    Audi Doodah Active Member

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    All looks good...peaks and troughs all in sync. The MAF is there to let the ECU know that air is entering the intake freely...no air, no bang. Actual airflow will always vary dependent on ambient temperature, air pressure, speed, etc so will never "exactly" follow the computer specfied value...nature isn't that predictable. Actual intake pressure will tend to vary compared to the specified as there's a time delay between the ecu seeing the required pressure , the n75 operating and the turbo vanes opening/closing and thus stabilising at the required pressure.

    Check out this site for all the info you could wish for on logging.

    Were you trying to diagnose any problems or just having a play???
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  3. swarcup
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    swarcup Well-Known Member

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    Wow thanks for the reply, I had a slight hesitation a few days ago, nothing much but it was there. Hasn't done it again thoiugh so thought i would do a bit of sniffing around. There are no faults stored in any of the engine,abs,electrics the only thing stored was a dodgy passenger door. So i thought i would see if things are working as they should. Im thinking a clean up of the intake manifold,inlet flap and egr may be needed.
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  4. Audi Doodah
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    Audi Doodah Active Member

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    Do a log of block 11 only, in 3rd gear from 1500rpm to the red line. Plot actual and specified pressure only. Your graph has too much going on and I'm thinking the actual pressure is a bit lazy now that I'm looking at it without tired eyes. Your Air Mass Meter (MAF) is defo ok though. Think of the MAF figure as a minimum air flow required for a given acceleration.
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  5. swarcup
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    swarcup Well-Known Member

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    i will but it maybe a few days until i can. If it is lazy what could be the possible reasons, n75, vac lines, turbo?
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  6. swarcup
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    swarcup Well-Known Member

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    turbo chart.jpg
    finally got it done, what do you think
    Last edited: Jun 26, 2013
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  7. Audi Doodah
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    Audi Doodah Active Member

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    Something isn't right as it doesn't seem to be holding peak boost. As for why...I'm not sure. A dodgy MAP would give spurious readings and there's nothing to suggest the turbo isn't doing what's asked of it. It could be your N75 not regulating correctly as you have 3 different extremes when coming off boost. Certainly not sure enough for me to suggest you go spending money on a new one.

    Here's some of my boost logs for comparison. Note how my smaller 1.9 turbo picks up quicker. You can also see how the turbo overboosts slightly as desired boost is hit and the vanes open fully. Always lagging when coming off boost too, as expected.

    Boost Plots.jpg

    https://dl.dropboxusercontent.com/u/103952776/Boost%20Plots.png


    Attached Files:

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  8. swarcup
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    swarcup Well-Known Member

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    Thanks for the reply there is deffo something not right, I have noticed that when the engine hasnt fully warmed up the boost is much better and if you feather the power in it also seems to be better. A bit of investigative work needed. I will keep the thread updated as i change or inspect various parts
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  9. Audi Doodah
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    Audi Doodah Active Member

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    The logical approach would be to start with the easiest/cheapest options first. Check and clean EGR, intake manifold (could be sooted up and restricting air flow but then 'blowing through' the soot and causing momentary boost drop???) and MAP sensor and Mr Muscle the turbo. Then look at swapping out the N75 and/or MAP. After that...well, it starts getting expensive.

    Fingers crossed it's an easy fix!
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  10. czm
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    czm Member

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    Sorry to hijack the thread
    I have been having this same issue and not sure what it is.
    Unfortunatley I dont have access to VCDS but I have the same symptoms.

    Please keep us posted with your investigations.
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  11. Audi Doodah
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    Audi Doodah Active Member

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    So you're gonna let Swarcup invest his time/money on fixing your fault!?!? :laugh:

    Just shows how useful VCDS can be...no fault codes but still helps to pinpoint the problem area/system.
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  12. czm
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    czm Member

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    OOhh I'm sorry. I was under the impression these forums were here to help and assist members in the Audi community.
    I have and will continue to investigate the issue and will happily FYI the thread to assist where I can.....

    now if you excuse me if off to purchase VCDS, a ramp, full set of tools and every single imaginable diagnostic tool so I don’t have to ask for help on forums anymore!!!
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  13. Audi Doodah
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    Audi Doodah Active Member

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    I was just pulling your leg, pal. :sm4:
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  14. czm
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    czm Member

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    doh :friends:

    Man I need to chill out.....
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  15. Audi Doodah
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    Audi Doodah Active Member

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    :friends:
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  16. swarcup
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    swarcup Well-Known Member

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    cheers for your help audi doodah its always worth a second level headed look at a problem that we don't understand and czm if you can contribute then please join in as you may suss out the problem before me, im not turning away any thoughts. I have however blanked off the egr valve and mr muscled the turbo( deffo made a positive difference). I removed the inlet manifold to have a butchers but only the main section not the two pieces that connect to the head and yes you are correct it is sooted up but there is still 75-80% of the bore unrestricted but first place to start is cleaning and while im at it I will remove the inlet flap and clean that up also as I had a look and that probably is still original and pretty gunked up. I will probably have a go this weekend if the rain stops. I will post a few pics as I go. :thumbsup:
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  17. Audi Doodah
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    Audi Doodah Active Member

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    Not a problem! I'm actually on Vagcat now swotting up on the V6 engine layout :uhm:
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  18. czm
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    czm Member

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    That would be awesome m8
    Is Mr Muscle ok to use on the turbo and how do you do that?
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  19. Audi Doodah
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    Audi Doodah Active Member

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  20. swarcup
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    swarcup Well-Known Member

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  21. Audi Doodah
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    Audi Doodah Active Member

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