[Biturbos4] B5 V6 "unilateral" misfiring

Chris Newbold chris at newbold.org
Mon Apr 21 04:38:02 PDT 2008

On Thu, Apr 17, 2008 at 4:55 PM, Chris Newbold <chris at newbold.org> wrote:

> Thanks for all the suggestions. I've started trying to decipher the
>  wiring diagrams to see if I can find some common points for the
>  left-hand side ignition or fuel injection. Many bits on the left-hand
>  side of the engine appear to utilize a single grounding point
>  underneath the coolant expansion tank... I'll keep everyone posted.

There appear to be only two grounding points in the engine
compartment: (1) a post beneath the coolant expansion tank where most
of the fuel and ignition wiring is grounded; and (2) the grounding
strap for the engine block.

I cleaned and tightened (1), though it already appeared to be in
excellent condition. (2) is pretty much inaccessible without
dismantling stuff from below.

I also visited every connector on the top side of the engine and
applied contact enhancing goo to each internal pin. Almost all
connectors already appeared to be in pretty good shape. The only
exceptions were three located just under the coolant expansion tank
and quite close to the hot side of the turbo. The connectors were
clearly heat-stressed, but appeared to be okay electrically.

The other main grounding point is at the bottom of the A-pillar by the
dead pedal. I checked that one too, and didn't find any issues.

There has been no improvement in the misfire situation. Not
surprising, since I didn't really find any bad connections. If it's a
wiring issue, it's gotta be something buried in the harness at this

I'm thinking this might not be electrical after all...

2001.5 S4 Avant 6spd

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