Knock sensing and retarding ignition

[Stephen Webb]

> > I've been reading the posts about knock sensing and retarding the
> > ignition. Now I am wondering, would it be possible to build a
> > simple,cheap device that would retard ignition as boost rises on a
> > turbocharged engine. I know MSD makes such a unit, but i think it is
> > much too expensive.
> > Regards Mads Rose Rasmussen

I have thought about doing this, and may, as time permits.

I have a motorola MPX something or another map sensor (2.5 bar?), National
LM1815 (? I think) variable reluctance negative slope zero crossing
detector IC.  To glue it all together in an intelligent way, I have a
PIC microcontroller.

Basically the idea is to use the ADC on the pic to read the MAP signal,
and either compute or look up a retard value. 

The LM1815 will hook in to the hall sensor on the distributor, and will
trigger an interrupt on the PIC.  If no retard value is needed, the pic
will just act as a "passthrough", introducing an insignificant delay ( <
10 uSec)  If a retard value is needed, the signal is delayed before being
passed on to the ignition controller. 

*I have experience with pics, and I was able to interface with the MAP
sensor too, but I have had trouble getting the LM1815 to work with my
distributor.  I believe I may be playing with a bum distributor.  I should
have another one in a few weeks to play with, and maybe I will get
something going again.

*I'm not sure of a "good" way to trigger the ignition module from the
pic.  Normally it sees the signal from the distributor, which I don't know
how to replicate, but I suspect there is an easy way to reliably trigger
the thing.  Anyone?

The MSD unit is the easier route, but I don't know how much it costs.  I
can tell you that I will have $40 tied up in parts for this project, for
whatever that's worth.


-Steve


----------------------------------------------------------------------------
To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org