Technical > Wiring & Sensors

rev counter input?

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Seight-v8:
hiya all,

Just building the loom for my vems ecu to run a rover v8 4.6 engine.

As its all electronic with coil packs, and that i no longer have a coil to take the engine rpm from.

Where can i now get a rpm input for my vdo rev counter.

Can i configure the ecu to supply the rpm reading somehow?

cheers

scott

rob@vems.co.uk:
There are a few options - using the Stepper to send a +12v signal to the gauge, or to use a pull-up resistor (about 500ohms) between 12v and the tacho line (tacho to a spare driver).

Then use the Extras->Tachometer Output Settings to control the line

Seight-v8:
rob,

wow you got me there, please allow for the fact i am a very newbie in this area.

Where do i take the wire (output) from the ecu from???

I know there are some spare channels, but i dont know what i can do with these or how to use them...yet

I could looking at the vdo info, use the W pulse from the alternator, but i dont know how accurate this could be.

As i dont really know how my ecu is configured, as dnb supplied it, but i havent powered anything yet.

thanks again

scott

gunni:
You can select one of the relay channels. Which is a P259 channel.

When you have done that the ecu is giving out a square wave that is the tacho signal. This is a grounding signal.
So you´ll need a pullup for it to register with the tacho.

You do that by connecting from a 12V wire to the tacho signal through a resistor, something like 2000ohm´s works fine.
Similar to this.

dnb:
The tacho should be configured as P259 output 4 (EC36 pin 3)

You can change this to any output you have spare, but you're a bit limited on spare output because it's a v8 with a stepper motor... ;)

If your tacho is expecting a signal from a coil, it is unlikely VEMS (or any aftermarket ECU) can drive it without a tacho converter box unless the tacho itself can be configured to accept low voltage inputs.  The converter box is a simple thing containing an inductor, resistor and diode, so it's possible to make one.

And as you say, there's always the W pin on the alternator.  But like you I am unsure how good this is.  It does work for diesel Land Rovers I suppose...

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