dist. hall signal, 62 degrees BTDC too (like crank)? [was: Re: 034 EFI]

[auditude at neta.com]

Hi again,

I think I may have found another typo (not trying to pick on
anyone!), in a post last month regarding the function of the MC/3B
ignitions (and incorporating them into aftermarket efi systems).

However, it might not be a typo, and I want to make sure I give the
right info to those configuring my replacement ECU! :-)

Below it says that the "distributor" hall sensor signal for Cyl 1
(compression) TDC is 62 degrees BTDC.

We determined that the "crank" timing reference pin is located 62
degrees BTDC.  But until re-reading this post below, I was under
the impression that the "distributor" signal occurs at 0 degrees
TDC for cylinder 1 at the compression stroke.

So, either the distributor hall sensor sends its signal 62 BTDC or at
TDC, relative to no.1 compression stroke.  Which is it?

I also read that the duration or window size for the distributor hall
signal is 40 degrees for the 20v 3B motors.  Is this spec the same
for the MAC11/MC-1's?

It would make sense, since it's probably the number of cylinders
that determines this spec, it's either facing the right
"neighborhood", or not, when the no.1 cylinder is at TDC (either
compression or exhaust strokes).

Thanks,

Ken

Orin Eman orin at drizzle.com wrote on Wed, 5 Dec 2001 21:34:52 -
0800 (PST):

"When using a crank sensor, if you want to determine
compression/exhaust stroke, some kind of cam linked sensor is
required.  On the MC and 3B engines, it's a hall sensor in the
distributor with one window centered 62 degrees BTDC on Cyl 1."

from:
http://www.audifans.com/pipermail/quattro/20011206/041044.html
>
> > > As with any EFI system, 034efi can be configured with a hall
> > > sender on the crank too by mounting a hall sender to read off the
> > > crank.  It is up to the installer how much effort they would like
> > > to put into the installation to effect certain advantages.
> >
> > How would this work?  Don't you need a signal that represents the
> > top of the compression stroke for each cylinder?  Unless I'm
> > mistaken I don't think you can get that from the crank since you'll
> > be getting the top of the exhaust stroke too.  Don't want to be
> > firing those injectors then.. unless you want some jet propulsion as
> > well ;-)
>
> Except at low RPM (ie. idle), when you can get slightly lower
> emissions by timing the injection to a certain point in the cycle, it
> doesn't really matter when the injectors are fired.  Remember they
> fire at the back of the intake valve, not into the chamber itself. In
> fact, when developing high power, the injectors are likely to be on
> 85% or more of the time.  To make things easy in the ECU, the
> injectors often are fired all at once - known as batch mode.  Thus
> each cylinder gets its injector fired at a different point in its
> cycle.
>
> When using a crank sensor, if you want to determine
> compression/exhaust stroke, some kind of cam linked sensor is
> required.  On the MC and 3B engines, it's a hall sensor in the
> distributor with one window centered 62 degrees BTDC on Cyl 1.
>
> For timing fuel injection, it is simply unnecessary to time the
> injection accurately unless you are trying for that last little
> reduction in emissions... not a concern of the 034efi system.
>
> Orin.