2.5l MC

[Gerard]

I might have asked before, but does anyone know what this knock
frequency is for the MC engines in standard form and perhaps with the
20-valve units? How does the Hitachi units on the cars pick up knock and
do they monitor different frequencies at different rev points or
something like that? I know they do knock detect above 3000rpm, or so I
recall. But how does it do it? As I'm not clued up on knock detecting
I'm pretty keen on learning on how it's done. Looking at the Hitachi
MAC13A ECU I have it seems it is alot of signal conditioning and
filtering and then perhaps a single signal to the CPU, like a low-pass
filter with an output that that triggers a CPU interrupt. Don't know.
Who does? What frequency is it watching for and does it watch
differently for different rpm/loads?

I've made my mind up on a Haltech ECU for "the next project". :) No
knock detect. A friend would be real interested in cooking up a knock
sensing unit, but I don't want to sit through alot of "reverse
engineering" of the Hitachi unit (I bet it's simple, but it's me we're
talking about here who has to do it! :)).

G.