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[2 Svo] Flemming's knock theory - question (fwd)



Cory Erickson wrote:
> I didn't think NOS was a "fuel"...just an oxidizer...

If you add too much Nitrogen, it decreases [effective] octane cause it
accelerates the burning process. Nitromethane, nitroglycerine, etc. 

> In my experience
> the EEC-IV in the 2.3 Turbos use the vane in the distributor simply for a
> reference point for spark dwell and injector firing. Because of this
> system, it is impossible for the computer to know what the exact position
> of the crank is...it only knows that the vane representing _some_ cylinder
> just went by the PIP, so now it can wait a specified time unit based on
> other engine info before it collapses the field of the coil and causes a
> spark at the NEXT cylinder in the firing order. This is how the computer
> can "advance" the timing from the base, but NOT retard it past the base.

You're saying the same thing I am, but you just haven't read all of my
articles. Since the EEC can only know that the engine speed changed when
it gets the next PIP pulse, it can only guess when to send the next
spark signal (SPOUT to the TFI) by adding time (converted from
rotational angle displacement to milliseconds by the EEC - it's very
good at that) to the last PIP so firing #1 at 40 degrees BTDC would mean
to send the signal at 130 degrees (again, computed in time) AFTER
cylinder 2 PIP pulse (the actual number of the cylinder is not
important). Anyway the knocking can only occur very soon AFTER the PIP
pulse, not before (or the engine wouldn't rotate the proper way,
right?).

If you read the rest of the message(s) - again, not a flame but I've
written several in-depth articles on this issue in the SVOOA Turbo Times
and don't know which one(s) you've seen.  It could also be that you have
a defective knock sensor too. But I agree the 87/88 TC's are more
sensitive to knock in the part-throttle, mid-RPM range than the SVO's
are - at least my 87 TC is and it has collected quite a few discarded
SVO components over the years.

You may have noticed that I also referred to the typical Toyota and
Honda system that has 360 little slots and 4 or 6 larger ones in its
distributors sensor system and this allows their electronic control
systems to be much more accurate.
 
> So how can the software get smarter when it comes to listening for knocks
> if it has to "guess" where it's at? 

Well, if it has to guess where to listen for knock could it possibly
know when to send the SPOUT signal? It is all calculated from the last
PIP signals. Good questions - sounds like you're ready to do some
research and study how these things really work  and learn what the
limitations are - see below.

> My guess would be
> that's why Ford played with the location of the knock sensor on the
> 2.3's...

The manifold design was changed cause the early (wide one) made it's own
noises that just happened to be near the same frequency as the KS and
were annoying to owners (cause the engine was ringing all the time). The
later manifolds are much more rigid and the engine is much quieter
because of this. The KS has two locations on the lower manifold -
pointing at the LF shock tower, parallel to the front axle and pointing
rearward from the lower manifold parallel to the brake master cylinder.

The first position was used in a limited number of installations but it
was quickly determined that a high percentage of these were broken at
the factory during engine installation - expecially on the XRs - so it
was moved to the rearward pointing location.

I inquired many years ago if there was a different programmed knock
signature between the two locations and got someone's name, but that was
10 years ago and I was not able to reach him for comment then.

> do you have any proof that this "knock algorithm" exists? This is
> by no means a flame...I am very curious how Ford implemented this "scheme"
> of listening for knocks.

Are you asking for reference material that you can research? Do you have
access to SAE papers? Start with 840251.

> In my experience, again, my '88 TC stuff is very sensitive about
> connecting the knock sensor. If I connect it, I slow down enough to "feel"
> it...this is with 92 octane, stock timing, stock ignition, and 15-16
> intercooled PSI.

And the engine was calibrated using Indolene so the current 92 octane is
quite inadequate. BTW my 87 TC pings a bunch too (see note above).

-Mike Fleming (one "M")