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Help!! A4 Running fault!

Discussion in 'A4/S4 forum(B5 Chassis)' started by matt_simo1, Apr 4, 2011.

  1. matt_simo1
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    matt_simo1 Member

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    Hi all, well i own a A4 Quattro 1.8T AJL Engine and it has a running fault which cannot be fixed?....what ever the throttle position when you floor it it stutters and mis fires a little then carries it thorough and is using an amazing amount of fuel? ideas??.....Now before you start im a mechanic and no my way around a car so scanned it and fault codes (N80) (N75) (G70) Came up....which is charcoal filter short to ground......boost pressure control valve short with ground and Mass air flow sensor signal to low....so i replaced all units and still same fault and same codes....i used 3 different scanners from a snap on modis to VAG-COM Bosch ones and still the same result....i have checked the spark plugs they are fine as well as replaced the fuel pump relat as all wirirng seems to got through that on a wiring diagram....i have also with a multi-metre checked the injectors and coil packs and all seems fine? the turbo hoses and and all vacuum pipes seem ok ad well so any ideas??

    Many thanks people Matt
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  2. 2thumbs
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    2thumbs New Member

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    HT leads?

    I assume you cleared the faults you mentioned after you found them...
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  3. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    You've got a short somewhere.

    N80, N75 and MAF harness all runs together along the bulkhead, then over to the airbox area and its far too coincidental that all three have broken with "short to ground" codes.
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  4. matt_simo1
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    matt_simo1 Member

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    Yea that's what I thought....but I tested the wires and by passed them but no difference?. And yes I cleared the fault codes after. Which makes me think possible ecu fault maybe? Cheers guys
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  5. matt_simo1
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    matt_simo1 Member

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    Just realised i never let peeps know what it was........right are you ready?.......................................................ENGINE MANAGEMENT FUSE MISSING...............

    dont ask me how...but several hundreds of pounds later a 100 pound diagnosis check from a Audi Dealer and lots of time, i realised the fuse was missing. I believe its down to some idiot at my work trying to be funny.. but there you go. Concerning that not any of our VAG GOM or snap on scanners let alone the Audi dealer not picking up on it.
    But its sorted if you was wondering.
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  6. murran
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    murran Active Member

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    and your a mechanic?
    sorry, but looking at the wiring diagram and realising those components are all powered thru one fuse....... checking that fuse's presence and condition would be my first priority. well before shelling out cash for three new components..... theyve all gone faulty at the same time have they? durrrrrrrr.

    makes me wonder what "service techs" have been looking at it. lol. :)
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  7. matt_simo1
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    matt_simo1 Member

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    Well that was the first thing i checked....i checked the fuses that where present...i didnt think i would have to check the fuses that were missing? why would i as i didnt remove any and they dont just fall out?.....but its a lesson learnt.
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  8. murran
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    murran Active Member

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    years ago i had the same problem on an a3 i think it was.
    the guy had had an alarm fitted and since then his engine light was on. after a bit of checking i too found one of the engine management fuses simply missing. anyway i put a fuse in and it blew straight away. checked the feed to the components that the fuse fed a live too and they had continuity to ground. odd i thought. then i looked at where the alarm fitter had mounted the siren...... he'd screwed it on with inch long self tappers to the baulkhead..... bang on the other side of the baulkhead was the engine wiring loom! lol.

    but the guy haddnt removed the blown fuse prior to it coming in, so i can only presume the alarm fitted had pulled it out to hide his mistake.
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  9. matt_simo1
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    matt_simo1 Member

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    Lol, its a strange world sometimes, i was kicking myself though, because it is my car and i thought i knew the history i didnt check the missing fuses....i still to this day havent found out who did it, i think A) they were susprised it still ran B) when i started spending money they probably thought it had gone too far to own up!
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  10. Oranoco
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    Oranoco Well-Known Member

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    At least you're all sorted now :)
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  11. matt_simo1
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    matt_simo1 Member

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    Yea man, thanks....got new bits soon too :)
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