[V6-12v] Pinking under light throttle

[James Whitehouse]

Tom,

Thanks for that, I agree.

I can eliminate 1) as I always use 98 octane 'super unleaded' fuel, as well
as fairly regularly running 'anti-coking' fuel cleaner through the fuel
system. 2) is a possibility, as the head gasket is due to be replaced, as
you are aware (this might also explain the slightly erratic temperatures,
although this could also be related to the fan problem. 3) is also possible,
but there are no other running problems and I believe the ECU is a bit fussy
about the crank sensor (if there's a fault on startup, it won't allow the
engine to be started). 4) is also possible, although again I would expect
other running problems. Another cause could be a coked up combustion
chamber, though I doubt this as the spark plugs were all good in the recent
service.

The other issue is that, whatever is actually causing the knock, the knock
sensors evidently aren't doing their job, as they should be detecting the
pinging and retarding the timing to prevent it whatever the root cause.

I agree totally about any of the latter causes throwing error codes so I've
booked the car into the local garage on Tuesday to have the codes pulled.

Cheers!
James

> -----Original Message-----
> From: Tom Christiansen [mailto:tomchr at gmail.com]
> Sent: 30 August 2006 06:17
> To: James Whitehouse
> Cc: v6-12v at audifans.com
> Subject: Re: [V6-12v] Pinking under light throttle
> 
> James,
> 
> Pinging happens when the fuel/air mixture is ignited at TDC of the
> piston. Reasons for why this could happen (my speculation).
> 
> 1) Low octane fuel.
> 2) High compression (wonder what happens if coolant seeps into the
> cylinder through the cracked head gasket).
> 3) Crank sensor is getting sick. Can't sense TDC properly.
> 4) Incorrect fuel/air mixture I suppose. The knock sensor should take
> care of this.
> 
> I believe both the crank and knock sensors will throw a trouble code
> if they become ill.
> 
> Tom
> 
> 
> On 8/28/06, James Whitehouse <james_whitehouse1 at yahoo.co.uk> wrote:
> > Another one for your perusal:
> >
> > I have some light 'pinking' under light throttle. It appears to be at a
> very
> > specific point of throttle pedal travel, just past idle, and will not
> occur
> > when you accelerate a little harder, or at WOT.
> >
> > We may find, while stripping down to do those head gaskets in a few
> weeks
> > time, that everything is 'coked up', but I'm dubious as I always use
> premium
> > grade 'super unleaded' fuel and regularly run a fuel system cleaner
> through.
> > Plus the spark plugs were still perfect when checked recently, after
> 30,000
> > miles, so I'm thinking the combustion chambers are probably all good.
> >
> > Anything else that can cause this? Dodgy knock sensor, etc?
> >
> > Cheers,
> > James
> >
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