[20v] distributor swap - 7A & 3B

Kenneth Keith auditude at gmail.com
Thu Mar 30 13:52:05 EST 2006

Doh!  Sorry about the premature emailiation.

I guess the urq's timing is controlled by the ecu but doesn't do
anything related to knock detection?  I don't have an urq so I can't
and won't argue, but it does seem strange that the crank (rpm/timing)
sensors would do anything without a single window wheel to determine
what cycle it's on.  I recall that urq's have the timing pin in a
different place, but I would think that the timing wheel would still
have to overlap the hall window in order to mean anything to the ecu.

I'm not very familiar with the NG motors at all except that they are
higher compression and larger intake valves than the earlier 10v's.  I
am surprised that they have 5 window dizzy's if they are knock
sensing.  Do they have one knock sensor or two?  7A's and 3B's have
two, which I think is because the ECU can distinguish between knock
and other noises based on which cylinder could be knocking as measured
by crank position.  How would a 5 window dizzy allow the ECU to know
which cylinder could be knocking if it doesn't know the position of
crank "and" whether it was compression or exhaust stroke (or is it
power versus intake)?  Even the single-knock sensor MC's without the
same cylinder-selective detection sophistication as the 2-sensor
setups have a single window dizzy.

I'm not disagreeing without having them in front of me, but the logic
escapes me.  If you can have knock sensing with a 5 window wheel, then
why have a 1 window version?  I just want to understand better if
anyone knows.

The gears that mate with the cams on the 10v versus 20v distributors
are different enough that it seems like it would make them
non-interchangeable in addition to the number of windows in the hall
sensor shield cup thing and the other differences mentioned.



On 3/30/06, Kenneth Keith <auditude at gmail.com> wrote:
> That makes sense.  I made the connection about the crank timing
> measuring, but I didn't see the point of the 5 window distributor on a
> system that uses the crank timing sensors for anything.  I guess the
> urq
> On 3/30/06, Ben Swann <benswann at comcast.net> wrote:
> >
> > Ken,
> >
> > The single window hall sensor does not really indicate the engine has knock
> > sensing, and is also used on the earler Ur Quattros without knock sensing.
> > Also, the later NG/NG have 5 window hall sensor and knock sensing too.
> >
> > It has more to do with the use of the flywheel sensors that identify Top
> > Dead Center and count number of teeth – RPM and Speed sensors.  These are
> > synchronised with the single window hall signal.
> >
> > Except for the wheel, the distributors are more or less the same – some use
> > a vacuum advance and some don't and the sonnector style, cap and rotor
> > change – so they can have more part numbers I suppose.
> >> > Anyway, the upshot of this is that the 3B and 7A distributors are
> > interchangeable and pretty much identical.
> >
> > Ben
> >
> > From: "Kenneth Keith" <auditude at gmail.com>
> >
> > Actually, that's incorrect.  7A's have knock sensing ignition too, and
> > therefore use a single window hall sensor setup.
> >
> > Ken

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