[Biturbos4] B5 V6 "unilateral" misfiring

Aegerter, Paul A AEGERPA at cpchem.com
Thu Apr 17 14:45:24 PDT 2008

Two thoughts based on experience with other cars...I've had no problems
with my 2.7T like this.
	1) Is the fuel pressure to the two banks separately regulated?
If so, could you have a lean or rich misfire situation going on because
the driver's side is over-or-under set pressure?
	2) Many moons ago, in a 1966 289 Mustang, we had serious
misfires on the driver's side of the engine...separate dual exhaust
pipes revealed one side running smoothly with lots of exhaust volume,
while the driver's side was VERY rough with very low exhaust flow.
Turned out there was a valve in the exhaust for heat-up that was rusted
closed, constipating that side of the engine (and forcing much of the
poorly burned exhaust up through the heating channels of the exhaust
manifold and out the passenger side!).  I wonder if you could have a
blockage problem between the exhaust valves and the resonator (where the
two sides come together)...a bad turbo, collapsed pipe, clogged
converter...leading to a quenched ignition?  I think the ECU will detect
this type of misfire as well as ignition-induced misfires...you can't
detect it at the exhaust outlets because of the interconnection at the

2002 A6 2.7T Sport
APR ECU, Bi-pipes, Magnaflow exhaust

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Today's Topics:

   1. Re: B5 V6 "unilateral" misfiring (Robert Myers)


Message: 1
Date: Mon, 14 Apr 2008 12:59:32 -0400
From: Robert Myers <bob at chips-ur-s.com>
Subject: Re: [Biturbos4] B5 V6 "unilateral" misfiring
To: "Chris Newbold" <chris at newbold.org>
Cc: Bi-Turbo Audi S4 Audi Fan Group <biturbos4 at audifans.com>, "Long,
	Scott G A1C USAF AFMC 88 SFS/S4W" <Scott.Long2 at wpafb.af.mil>,
	list <quattro at audifans.com>
Message-ID: <auto-000000060702 at chips-ur-s.com>
Content-Type: text/plain; charset="us-ascii"; format=flowed


Let me preface my comments with "I have exactly zero experience with 
that V6 engine and its ignition system" so feel free to completely 
discount what I have to say.

The stock ignition of the earlier 5 cylinder s-cars operates in this

1.      A full time +12v is applied to one side of the primary coil 
of each ignition coil at all times.
2.      In response to a signal from the ECU, the POS breaks the 
connection from the opposite side of the primary coil and shuts off 
the connection between the opposite side of the primary coil and ground.
3.      This collapses the magnetic field of the primary coil and, in 
turn, inductively generates a very high voltage across the secondary 
coil.  This high voltage is what fires the spark plug.

Potential problems include 1. failed POS, 2. failed (or failing) 
coil, 3.  low voltage to the primary.  4. maybe something else.

It sounds like you have fairly well eliminated the POS and coils as 
the source of the problem.  This leaves a low voltage to the primary 
as a possibility.  This could happen as a result of corrosion at the 
connector for the coil (this is, on the AAN engine, at a white 
connector on the firewall) or some other high resistance spot in that 
circuit.  This could be worth checking.


At 12:15 PM 4/14/2008, Chris Newbold wrote:
>On Mon, Apr 14, 2008 at 12:03 PM, Long, Scott G A1C USAF AFMC 88
>SFS/S4W <Scott.Long2 at wpafb.af.mil> wrote:
> > Is there an ingnition control module that tells the cylinders when
> >  fire?  Do the coil packs on bank 2 share any common ground wiring?
> >  about common 12+ wiring?
>I believe the components involved are the 6 per-cylinder coil packs,
>the 2 per-bank output stage amplifiers and the engine ECU. So other
>than the amplifier doohicky, there does not appear to be any other
>component which is bank 2 specific.
>I'll have to pull out the Bentley wiring diagrams and trace everything
>down to see if there is any bank-specific shared wiring. This seems
>likely, though. I was vaguely hoping that someone might have some BTDT
>experience with this and would say "Look _there!_"....
>2001.5 S4 Avant 6spd
>2004 allroad 2.7T
>quattro mailing list
>quattro at audifans.com
>Watch this space for ads :)


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