Air metering valve - MC-2

[james accordino]

--- isham-research.freeserve.co.uk at pop.pol.net.uk,
quk at isham-research.freeserve.co.uk wrote:
> One of the many outstanding jobs on Puff the Magic
> Wagon is the
> replacement of the fuel metering head.  I've had the
> typical symptoms
> of upper O-ring failure for some time.
>

What are they?
 
> As always, there's a knock-on.  The CO adjusting
> screw in the metering
> valve is so rounded out as to be useless.  
> I have, however, a metering valve from an MB engine
> on the shelf.
> According to Audi's documentation, the MB valve is
> 034 133 471J.  Hmm.
> I have 034 133 471M.  The valve from the MC-2 is 034
> 133 471L.  As far
> as I can see (I've measured the bowl/cone) the only
> difference is
> that the potentiometer on 471M has its three-pin
> connector parallel to
> the body and the one on 471L is normal to the body. 
> 471M is mounted
> very close to the MB's inlet manifold, so it makes
> sense to turn it -
> 471L is mounted the other way round and there's
> plenty of room for
> a straight connector.
> 
Short of opening it up and measuring the diameter of
every drilled hole, I think you're doing the prudent
thing.  Test it's suitability on car (CO readings,
plug color)?  If it seems to perform well then I guess
you've found your answer.

> So I'm taking the potentiometer off the 471L and
> putting it on the
> 471M - hoping this will give me a usable air
> metering valve.
> 
You have identified what probably produced the suffix
change.  They have changed suffix for much less than
that.  The change from a hex-head bolt to a socket
head for an adjusting screw is enough to trigger this.
 I believe the VAG parts interchange is much larger
than documented if you are will to transfer some
ancillary items.

> Anyone any comments?  Source of a good adjusting
> screw for less than
> $1200?
>
Can you use the adjusting screw from a much more
common (cheap) metering head?  A 4 cyl. maybe?  It
would be worth it to salvage a head you might actually
need.
 
> I'd like to resolve the 471J vs. 471M issue, too. 
> Audi doesn't document
> a change on the MB at all - but a lot of funny
> things were done to the
> MB engine half-way through production.  Is this one
> of them?  What
> exactly was the change - the volumetric
> characteristics of the engine
> didn't change?
>
It would be really cool to find out the product
updates as they occurred.  Every ordered change,
whether at Audi or Bosch has documents describing
cause, proposed solutions, costs/benefits, etc.  They
won't change gasket paper without a document trail. 
It would certainly make our jobs easier.  
 
> The list seems to be down at present.  I hope it's
> not permanent.
> 
Me, too.  The ISP that I use went belly-up in early
Dec. and I thought something like that might have
happened to Dan's.

Jim Accordino