SR aftermarket tacho signal

[smokey_tires]

I'v had a thought.....

The tacho signal is a pulse correct? Each coilpack creates it's own pulse which feeds into one wire and into the ecu, correct?

Well in theory that single signal wire shouldn't have a continuous flow if power feeding through it, therefore pulsing.

I was thinking that if I splice my tacho "signal" wire into that single pulsing wire it should give me a tacho reading. Is this true or is it only in theory, not in ppractice

[JohnnoEH]

I think you're right, but from my hazy, unreliable memory the voltage is higher from that signal wire than it is from the standard dizzy signal. I thought there was usually an actual tacho signal out from the ECU on SRs and RBs, but could be wrong.

If you've got an aftermarket tacho, make sure that it can handle the extra volts or you'll fry it. There is a way to get it working for the standard tacho, I think it involved running an extra wire into the signal feed with a constant voltage that's low enough to not interfere with the tacho (creating a parallel circuit which will drop the volts at the tacho). Or maybe it would be possible to use a resistor, which seems to be a simpler and smarter idea to me - but then again there's probably a reason somebody went to the trouble to do the above fix...

[smokey_tires]

Yeh there is a tacho out in my ecu but it doesn't give me a reading for some reason.

If this signal wire blows the globe in my test light then I know that i'll have to use a resistor

[JohnnoEH]

Just remembered these, there's an old 910bluebird.com writeup on this page.

http://www.aussiebluebirds.com/files/