Rpm signal

[washy]

hey, im a long time reader of the forums but first time poster ive been trying to find a rpm signal on my mk1 focus rs, but they all read exactly half the revs im doing! e.g. im doing 1200rpm it shows 600rpm. ive tried getting it from the ecu and coil pack but its just the same! any advice on where to get an accurate signal or how to boost the signal maybe?

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[tabetha]

So you have a FRS mk1, in which the tacho reads 1/2 ?
Hard to see how this can happen with the correct tacho, the reason why they read 1/2 is because they are for a conventional, ie non coilpack ignition system.
So the std wiring will be ok for this.
If I assume you are using some aftermarket tacho, most have switches to suit different cylinders amounts, so switch to different setting will sort it.
I don't know if this will work but is something I thought about before, and that is to take a reading from BOTH side of the coil negative, each through a rectifier diode, ie 1N5408, this will then double the signal, as the std coilpack tachos only sense one side.
tabetha

[washy]

thanks for the reply tabetha
i need the rpm signal for a turbo timer, ive tried everything i can think of but had no luck. i will give your idea a try and will let you know how i get on!

I wonder how other people who have fitted boost controllers, turbo timers and an additional tacho that require a rpm signal have got round this problem?
ive done lots of searches and other people have had the problem.

[tabetha]

I can't see why it would matter what the rpm reading was for a turbo timer, so long as it's getting a feed ?
tabetha

[washy]

it has 'cut off' switch where once the timer has started its count down, if it goes over 1800rpm it shuts off straight away. plus it displays the rpm so want it showing it accurately. Im expecting them rectifier diodes tommorow so il let you know if it works.