Lorenfb

"The knock sensors are tuned to be most sensitive to the frequency that the particular engine's bore size will cause the knock frequency to be"

Not totally correct -

Most ECMs, e.g. 928 EZKs, that utilize knock sensors use some form of signal
processing within the ECM. It's not as simple as an analog filter detecting a
certain frequency. The more sophisticated knock system converts the analog
freqencies from the knock sensors into the time domain (digital world) form
for digital signal processing which can significantly better analyze analog data.

Furthermore, the EZK unit functions as does the 964/993 DME unit by
retarding the actual cylinder where the knocking is occuring. The EZK
knows which cylinder produced the knocking by use of the Hall sensor.

BC

...This is false. There is no way for the EZK to retard an individual cylinder and leave the rest alone, as I believe you are trying to say here.
You may be misunderstanding the 928 systems.
The ezk MAY be able to retard a bank, but in my experience with the S4 system, I do not think this happens. The S4 system is two separate spark banks with thier own coils, caps, rotors, and signal (I'm not even sure the whole signal loop is separate)

Lorenfb

"...This is false. There is no way for the EZK to retard an individual cylinder and leave the rest alone, as I believe you are trying to say here. "

Read the Porsche manual (WKD 493 421) page 2 -18!

"The S4 system is two separate spark banks with thier own coils, caps, rotors, and signal (I'm not even sure the whole signal loop is separate)"

There's only ONE EZK unit and it knows ALL! It knows TDC and which cylinder is on the compression stroke. That's all that's needed
the determine cylinder IDs.

BC

This is true Loren - very true - as I stated in my response, I understand that there are two separate separate systems - and I also understand that there is ONE EZK.

Which Manual is that *title*... I have the actual Workshop manuals, and I have dismantled an entire S4 and am slowely putting it back together. I have specifically paid attention to the ignition system as am currently wiring and will install a standalone system for ignition and injection, etc.

Though there is ONE ezk, and there are TWO separate banks, there is no physical way the current design of the system can retard just one CYLINDER. Can it retard a bank? I'll hear some info on that if you have it - but please quote the porsche manual pages you state here so we can dispell some misinformation on your part or mine.

Lorenfb

"I understand that there are two separate separate systems"

There's only ONE ignition system, which includes two knock sensors, two ignition modules, two coils,
& two distributors!

Read the manual.

BC

Tell you what... Too much time on these boards is wasted on stuff like this...

I've been here a while, and I think people usually will take my writing as well-experienced.

I'm going to ignore this guy because he's being difficult.

FACT: The S4 can shut down one bank of the ignition "System" if it sees certain parameters. There is one ignition computer, but it sends signals to two separate banks of coils, caps, rotors, and wires.

FACT: The S4 ignition system has no way of individually changing ONE cylinder's timing. Physically impossible with the setup if anyone were to look at it.

When I say "Bank" I mean the 4 cylinders that are under the control of the one cap, rotor, and coil.

Lorenfb

'I'm going to ignore this guy because he's being difficult." - BrendanC -

The easy out! You need to read more and not guess at how things work.

I work with most all the Porsche shops/dealers in SoCal, i.e. for the last 20+ years.

So what do you do?

BC

....One more time.... Show me where this is proven on the 928S4 - that an individual cylinder is retarded.

macreel

gentlemen, gentlemen... refer to Bosch Automotive Handbook,
pp.496-497, wherein is discussed the knock sensors (2 or
more for 8-12 cylinder engines) and knock control for
INDIVIDUAL cylinder ignition & spark retardation/advance;
works in conjunction with engine speed sensors and maps
in memory.

Knock sensors are basically accelerometers whose analyzed
output waveforms trigger stored control functions.

G'luck.

BC

I understand that some information regarding this is published... But the 928S4 system cannot retard individual cylinders.

John Speake

I've never seen any information that says that the 928 EZK operates on individual cylinders. Although it may potentially play with the two banks of cylinders, I have never seen any information that says it does.

Even the imfamous and mis-named "ignition protection relay " only shuts off the fuel njectors of one bank or the other, the circuit is not linked to the EZK.

Let's stick to facts, not theories. otherwise we are pissing into the wind !

Z

That's where I saw it:

bd0nalds0n

So since the cams are always spinning at the same speed, and the distributors are fixed to the cams, the overlap of the rotor against the specific poles of the distributor is such that it permits the EZK to fire the coil at different intervals, thus varying the timing of each cylinder by as much as 9 degrees? Is that how it actually works? It seems like the electrical connection as the rotor spins must be equal to or greater than 9 degrees to permit that kind of variability...?

John Speake

OK, but it says "...the ignition timing on all cylinders will be retarded..."

bd0nalds0n

Only retards everything by 6 deg if the hall or knock sensors fail