[Diy_efi] Individual cylinder retard

[bcroe at juno.com]

There is no magic to different retard for different cylinders.
Use a counter equal to the number of cylinders and count 
ignition pulses.  Count to 8 for a V8, 6 for a 6, etc.  If a 
knock is detected when the counter says 5, make a note 
to retard the ignition pulse a bit more each time 5 comes 
up.  Same process for every other count/cylinder.

The retard circuitry in my J & S doesn't know which ACTUAL 
cylinder is which.  It just knows to retard the one which 
knocks every time it comes around.  It even has an output 
to tell the maximum retard, too bad you can't tell by cylinder.  Of 
course there are switches to set, to tell it how many cylinders.

If you have waste fire coils, you need in effect a knock retard 
system for each coil.  In that case you can tell within 2 
cylinders, which one is knocking.  You would need something 
on the order of a cam sensor input to determine an actual 
cylinder.

Usually the tendency of individual cylinders to knock is rather 
uneven.  The beauty of the J & S is that you can keep all other 
cylinders at/near peak power and efficiency, while retarding 
the offender(s).  The other problems of sorting knocks from 
noise are still there.

Bruce Roe



21 Dec 2002 Nick Starai <true at ItsYourDomain.com> writes:
> > how do you know which cylinder to retard by how much 
> > - especially at higher rpms, is there a low
> > rpm cutoff for this algorithm ?

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