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AFR readings with my car, are they correct?

Discussion in 'A3/S3 Forum (8L Chassis)' started by Dan s3 audi, May 28, 2013.

  1. Dan s3 audi
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    Dan s3 audi Member

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    Basically I have fitted myself a AFR gauge a few months ago. I have always noticed a humming noise when driving along motorways etc. But I have always put this down to tyres or gear box. I have noticed for example when my car is at idle it does not just stay at 14.7 but I continuously fluctuates between 14.7-15.1 and back. Now it also does this when I am cruising along the roads at a continuous speed giving a two tone noise from the engine that I thought was the gear box at first. Now I have a standard fuel pump in the car, 111k on the clocks now, and running a 4bar reg. could this issue with the AFR going up and down slightly be due to the fuel pump being tired? any other suggestions to the possible cause?


    Thanks
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  2. 16Klappe
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    16Klappe Princess Slayer

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    Potential air leak, always worth having a smoke test done.

    AFR will fluctuate slightly as the ECU adapts to the airflow and the atmospheric differences, 14.7 to 15.1 isn't a bad fluctuation though so I wouldn't be overly worried.

    What does it read on boost?
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  3. jonno123
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    jonno123 Member

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    as above thats normal ! what matters is what afr is under boost
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  4. Broken Byzan
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    Broken Byzan Photographic Moderator Staff Member Moderator

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    Why do you have a 4bar FPR in there?

    Have you checked block 32 in VCDS to see what LTFTs are?
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  5. 16Klappe
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    16Klappe Princess Slayer

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    Because it is an S3 Mark ;)

    Back to the A4's you go :p
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  6. Dan s3 audi
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    Dan s3 audi Member

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    Have you checked block 32 in VCDS to see what LTFTs are?[/QUOTE]

    Hi, sorry I don't know what your mean?

    No air leaks, when I took the car to B5 for the custom map all air leaks were checked. But if they are suppose to do that then that's fine. I thought that they had to hold a constant reading of 14.7 on idle. On full throttle I think it around 12.5ish, which I have read is fine.
    With the cars AFR changing while cruising its creating that two tone engine noise in sequence with the reading going up and down, so this is defiantly normal?

    Thanks
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  7. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    A4's typically came with 4bar fpr as std while transverse engines like the S3 have 3bar so his question is valid...

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

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    4bar fpr on a std car with make the ECU pull around 15% fuel out... absolutely no reason on the planet to fit one and if you think your pump is suspect then even less reason to use one as this will send it over the edge..

    Do as Mark suggests... use VCDS, log it on block 31 (assuming its wideband... lets face we have no idea what car/year etc you have or if it is std or not as you haven't mentioned this)

    fluctuating AFR is fairly normal... if your car is mapped and its doing 14/15s on boost then its a **** map <end/>

    If all you are worried about is cruise etc then don't worry... fuel pumps show signs of weakness under boost when they are forced to earn their living...

    If not mapped for the 4bar (assuming its std) then bin off the 4bar for a 3bar and save whats left of the life of your pump...

    <tuffty/>
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  9. Broken Byzan
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    Broken Byzan Photographic Moderator Staff Member Moderator

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    Back in your box Jardo, :haha:

    You 8Ls just want to own a bit of the B5, so you steal our FPR's However our pumps can manage it no problem and they are designed to because they left the factory like it :beee:
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  10. 16Klappe
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    16Klappe Princess Slayer

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    Our A3 pumps can manage 4 bar....On boost :p

    I knew that A4's/Passats had 4 bar regs, our friend Robin with the Scirocco I was talking about the other day didn't know that and was running a 4bar FPR on a standard map with a 3 bar pump.

    Poor lad.
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  11. badger5
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    badger5 RIP S3dave Site Sponsor

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    what engine code S3?
    why 4bar as others have asked...........
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  12. Dan s3 audi
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    Dan s3 audi Member

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    Car Spec as follows:
    B5tip
    Large port head
    low comp wossner pistons (I know I would have been better off with normal comp but at the time jabba sport said to put high comp in)
    re-bore to 82.5 bores
    rifle drilled intergrated rods
    4 bar reg (again jabba said not to get bigger injectors but put the 4bar in, bad advice I know)
    stage 3 spec ko4 cr turbo
    relentless v2 mani
    3" straight exhaust de-cat
    bored out inlet manifold
    welly cooler
    forge re-circ valve
    Not a wideband ecu (old version)

    Was mapped at jabba before last Christmas and had problems with map. Took it to bagger this year where he produced 305bhp from it. When on full bost its around 12.5-13mark, when cruising with no boost alternating between 14.7-15.1.
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  13. 16Klappe
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    16Klappe Princess Slayer

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    Under fueling slightly I believe, Bill and PT will be able to comment better but on the face of it I believe there should be roughly 1 part less air on full throttle.
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  14. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    Ah... k.. I have vague recollections of the car now lol... sorry dude, see so many cars :)

    Old non wideband lambdas are not the most accurate and depending on the actual map (all things considered) then I am not sure its something to be overly concerned about... tricky one to diagnose easily over a forum... maybe worth dropping Bill a call and see if he can dig up your dyno runs to see whats what... he may well remember the car once you prompt him...

    Where is the lambda for the wideband gauge?

    As mentioned before AFR does tend to fluctuate a bit especially seeing as the hardware setup is a little more exotic...

    <tuffty/>
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  15. Dan s3 audi
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    Dan s3 audi Member

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    That's okay, I know you must see a lot of cars go through bills workplace a week. I have a dyno print out with the afr readings when it was mapped. I will post them on the next post, when I have uploaded them. The afr gauge, which is a wideband, is placed on the de-cat pipe because I didn't have the resources to weld a new point on (just used an existing point). My main concern was the two tone noise when keeping at a constant speed from the engine. just like the engine is making a deeper then a lower tone. (which is consistent with the afr gauge going higher and lower).
    #15
  16. Dan s3 audi
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    Dan s3 audi Member

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    Jabba's map
    [​IMG]

    B5 map
    [​IMG]
    #16
  17. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    Humm.. an exhaust leak could cause fluctuations too... its quite far from where the normal readings are taken...

    <tuffty/>
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  18. badger5
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    badger5 RIP S3dave Site Sponsor

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    To further complete the Information, now I know what car this is.... You have sorted your Fuel Pump Issues now?
    afr ins 12.5:1 is ok, if its rising with revs higher than this, then its max'd injector duty cycle and or running out of fueling

    Remind me,.... your injector size is??
    #18
  19. superkarl
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    superkarl MAN OF STEEL

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    lol
    im gonna guess stock bill
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  20. badger5
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    badger5 RIP S3dave Site Sponsor

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    yea, but this car has had different stuff done to it...
    386cc std injectors @ 4bar ~440cc equivalents, which will max out at just over 300bhp.

    550's for the win on 3bar fpr ideally as my preference

    fuel pump(s) also have been an issue.... but I dont remember the details..
    #20
  21. Dan s3 audi
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    Dan s3 audi Member

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    Hi bill
    Nothing at the time was mentioned about the fuel pump, it was all running sweet at the time. They were standard injectors and still are atm. I am to come back to you with my new 550cc injectors and 3bar reg for a car check. This has been put on hold at the moment as I have just brought my first house and all my savings are drained lol.
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  22. badger5
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    badger5 RIP S3dave Site Sponsor

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    you had an inline pump but it was noisy so you were'nt running it? I think thats what I remember.. thats why I mention fuel pump.

    houses = bigger money pits

    :)
    #22
  23. Dan s3 audi
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    Dan s3 audi Member

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    Yes just working out my monthly bills for the house and its not looking good for the Audi lol. but its like with my motorbike, I re-built both the engines myself and put so much time into them I would not sell them off. Rather they sat in my garage until I have enough money to run them.

    Nope, I only had just the standard fuel pump on the car.
    #23

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