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really really **** MPG + flickering xenons

Discussion in 'A3/S3 Forum (8L Chassis)' started by rob_sri, Dec 20, 2010.

  1. rob_sri

    rob_sri If in doubt, flat out

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    temp sensor sitting at 60 n moving up slightly occasionally..

    awful mpg.. i mean like going slowly round and used like almost quarter of a tank getting back from work and driving to a friends house reasonably locally!

    sounds like coolant temp sensor maybe?

    does this sound about right before i buy one?

    also the person who fitted my brand new forged engine took out the knock sensors so i couldnt use boost.. till he plugs them back in and the engine is ran in.. would this affect MPG?

    also.. this next one isn't costing me but its embarassing!

    i have to sit there for like 5 mins flicking the lights on and off.. they will flicker and go off.. then one will come on and stay on.. keep flicking away and eventually they will both stay on!

    right nightmare!

    any ideas?
     
    #1 rob_sri, Dec 20, 2010
    Last edited: Dec 20, 2010
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  3. Alex C

    Alex C Well-Known Member
    VCDS Map User Audi S3

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    with **** mpg and your temp reading not going above 60 then i suggest your thermostat is broken
     
  4. rob_sri

    rob_sri If in doubt, flat out

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    well might as well change coolant temp sensor an the thermostat for what its worth if you think that this is likely to be the issue..
     
  5. DaveA3

    DaveA3 Audi A-Trizzle!

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    yeh i would say stat also.

    The flickering lights maybe dodgey earth. check the wiring isnt exposed to any water/snow
     
  6. rob_sri

    rob_sri If in doubt, flat out

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    aye looks like il be changing them!! never done one on an s3 what are they like to change? hard job??.. do you know where the earth for the lights may be? tbh i wouldnt have a clue!!!
     
  7. Alex C

    Alex C Well-Known Member
    VCDS Map User Audi S3

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    its not a complicated job to change the stat, just fiddly. Its on the front of the block but access to it is hindered by the alternator
     
  8. rob_sri

    rob_sri If in doubt, flat out

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    urghhhhh COLD!! haha :'(

    if it weren't so cold id be out there now doing it dammit!!!

    i think im going to have to man up and bite the bullet! this is starting to cost me a fair amount in fuel!!
     
  9. PetrolAholic

    PetrolAholic Member

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    be aware in cold weather cars do use more petrol anyway, maybe not on the level that you are going through it but it does make a difference.
     
  10. rob_sri

    rob_sri If in doubt, flat out

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    my engine builder doesnt reckon the stat or the temp sensor would even matter as the fuel is regulated by the air temps rather than the coolant temps

    anyone confirm this?
     
  11. leey

    leey New Member

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    I have just had to change my temp sender and stat. Was getting really bad mpg around 20 or so since they have been changed my mpg has gone back up to about 27.
    Broke my dip-stick tube guide at the same time when replacing stat as there really brittle and replaced the the dip-stick as well because that decided to fall apart as well.
     
  12. Alex C

    Alex C Well-Known Member
    VCDS Map User Audi S3

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    well when i told my VAG specialist mechanic that i thought the stat was dead because the temp reading on the dash was low he said it could just be the sender. Then i said the mpg had dropped and said ok, stat it is then...
     
  13. Fahim

    Fahim Member

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    Correct me if you believe I'm wrong, but the MAF usually incoporates what used to be known as a Air Intake Temperature sensor, which together both tells the ECU the amount of air coming into the inlet manifold and the temperature of the air so to know how dense the air was in relation to the fuel/air ratio.

    However, thats all fine but if your stat isn't working it won't tell the ECU when the temperature of the engine is at 90 odd degrees (optimum temperature on most cars) and so it'll be adding more fuel into the combustion chamber. Also if the thermostat isn't working and as you say the gauge is hovering aroung 60 degrees then your car is NOT working at its optimum temperature and over fueling is most likely the case. The Stat is obviously stuck open as to allow the coolant to flow continously through the engine and radiator providing to much cooling which is unnessesary and thus the engine counteracts this (by trying to heat the engine up) by running very rich.

    Hope this helps a little.
     
  14. ghill

    ghill New Member

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    I think it does matter because your ECU thinks your engine is cold so keeps the mix rich. Even in warm air temp the car runs a little richer when it's first started doesn't it?

    I've recently had the same issue with 60deg on temp gauge and did temp sender and thermostat at the same time. Makes sense while you have drained the coolant (though you could do the sender on its own with just a small coolant spillage if you're quick swapping them over)

    Since doing this my fuel usage has improved so I would advise getting the job done, with the Thermostat and Temp sender being relatively cheap items. Make sure you get the green temp sender which was an upgraded part from Audi as original black ones very prone to failure.

    Thermostat is an awkward job, you will more than likely break dip stick tube so get spare ready first.

    I was pleased to see that replacing these two parts solved the low reading on the gauge as the third possible problem of a faulty gauge in the dash sounded more difficult to sort out!
     
  15. rob_sri

    rob_sri If in doubt, flat out

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    aha see this makes sense and for how much they cost.. gotta be done!!

    my MAF could be faulty too maybe?? i think im going to do the stat and the temp sender whilst im at it! may as well!!

    any other possible reasons why i may be getting such awful mpg?

    i need a vagcom =/

    im really hating on my car at the moment! just treated it to a lovely new system and forged engine and this is how it repays me!
     
  16. ghill

    ghill New Member

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    haha - they have a funny way of doing that...after a long time behaving itself perfectly, mine developed an awkward misfire, faulty MAF, temp sender and thermostat days after i got it back from bodyshop after £100's of cosmetic work being completed! At least it's got a sense of humour!!

    oh well - it looks mint now but I'd have put off the paintwork if I knew it would need another £400 weeks later!!

    with your mpg, what does your trip computer display for your average? Most people with sensible driving get approx 33mpg, that's my commute mpg which is 25mile motorway 5 in city traffic (can get that down with sprirted driving in no time tho!)
     
  17. rob_sri

    rob_sri If in doubt, flat out

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    i think that maybe similar to mine!!! im not a fan of this humour its costing me too much!!

    how did you find out... vagcom?

    trip computer pfft its all over the shop.. you can see its running rich as its quite smokey and you can smell it a little! no where near 33mpg anyway!!
     
  18. rob_sri

    rob_sri If in doubt, flat out

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    To update.. My mpg on the dash is currently 19.7 but it feels worse than that!! Constantly at the pump! Need to get this sorted asap!!
     
  19. thorsy22

    thorsy22 Member

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  20. ghill

    ghill New Member

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    definately start with thermostat / temp sender - if your temp on gauge is only showing 60deg I'm sure one or both of those two bits are playing up and affecting the fuel usage. Mine wasn't that bad when I changed them and I noticed a difference straight away.
     
  21. rob_sri

    rob_sri If in doubt, flat out

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    went down to 19.3 today.. not happy haha specially seeing as im driving relatively slow in this bad weather!!! going to get thermostat and coolant sender tomorrow i think!!!
     
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  23. rob_sri

    rob_sri If in doubt, flat out

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    can realllly smell it running rich.... :(

    anyone with a vagcom near birmingham wouldnt mind lending their services??
     
  24. s3dave

    s3dave TFSI Hybrid
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    Check the pipes that lead to the evap/charcoal can under the left cover by the screen wash especially on the joins
    fuel smell can come from here and poor mpg
     
  25. aragorn

    aragorn "Stick a V8 in it!"
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    Change the stat.

    With the temperature low your running in cold start enrichment all the time (ie the "choke" is on).


    As for removing the knock sensors... WTF?

    Unplugging the N75 will have you actuator pressure, running without knock sensors is pretty stupid imo.
     
  26. Hadders

    Hadders Member

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    Quick thread hijack, but I had the sender replaced a little while ago and now mine appears to be running a little strange as well, so now wondering if I could need the stat. MPG is right down, circa 21mpg (usually at about 28). Temp gauge almost exclusively shows ~80 only showing 90 when the engine is really pushed hard. That and it has a habit of going into "overboost limp mode" (not sure what the technical term is) a lot recently. I have done the N249 bypass incidentally. Does all this behaviour sound like a potential stat problem? I don't get any fault codes... At least I don't think so. I'll check in a sec.
     
  27. rob_sri

    rob_sri If in doubt, flat out

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    its coming through the exhaust and fumes are quite white..

    i think stat is deffo to blame.. but would it be this severe? or maybe something else is at fault too =/
     

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