Rev counter signal

[Matra_Hans]

The rev-counter in the Murena: From where does it get the signal?
I am asking because I have installed a not original engine, and the rev counter connection from the new engine's ecu does not make the rev counter move.

thanks Hans

[Bart_Maztra]

Rev counter is getting the signal from the ignition coil. (the - terminal)

[Matra_Hans]

Thanks bart.
Too bad I have removed the original ignition system.

Hans

[JL]

Which engine are you using and do you run coil packs to provide the spark?
Regards
John

[Matra_Hans]

I am running a peugeot 505 Turbo injection engine (n9te) with a VEMS ECU and a Ford ignition pack (wasted spark) but I am sure that we can find a signal (from the ecu) for the rev counter.
Hans

[Matra_Hans]

You can see and hear the engine here: https://www.youtube.com/watch?v=ctYrQGqC9bM
hans

[JL]

OK, I think that I have read that you can take a signal from the supply to the coil pack that will run the older type of rev counter. I will try to find the article just in case I have been dreaming this!

John

[JL]

I think this was the thing that I saw:

http://trigger-wheels.com/store/contents/en-uk/d32.html#p129

Regards
John

[JL]

Also read this thread it may help you.

http://www.turbosport.co.uk/showthread.php?t=178208

Regards
John

[Matra_Hans]

Thanks John: That was some usefull links. :-)

Hans

[Bart_Maztra]

Thanks bart.
Too bad I have removed the original ignition system.

I guess there still is a coil? Then hook it up to the negative terminal.

[Matra_Hans]

Hi bert: I am using a Ford coil pack and I am running a wasted spark setup i.e. the spark is fired during the compression stroke and an additional spark that is wasted is fired during the exhaust stroke. Therefore I have twice the number of sparks per revolution compared to a traditional distributer and coil ignition; consequently I will assume that the rev counter will show the double of the actual revolutions.
Hans

[roy4matra]

I am running a peugeot 505 Turbo injection engine (n9te) with a VEMS ECU and a Ford ignition pack (wasted spark) but I am sure that we can find a signal (from the ecu) for the rev counter.
Hans

If you are running a wasted spark system then usually the coil is a twin coil pack, so one 'half' of the coil pack is switched on and off but it fires two cylinders at that instant one of which requires the spark and the other that doesn't (hence wasted spark).  Then the next time it fires the other 'half' supplying the other two cylinders.

So the ECU is switching back and forth between the two coils in the coil pack.  The idea is that each coil has twice as long to recharge.  The Murena tachometer requires the signal from the negative side of a single coil which is something you are not going to get from the ECU you have as it is using two different circuits; and you cannot join the two signals without isolating them otherwise you would short the two circuits together.

However, if you took the switching signal from one coil and doubled the signal that should give you the required pulse rate to drive the Murena tachometer, provided the voltage was correct.

Roy

[Oetker]

Just a flash of the mind.
Isn't it possible to collect the puls from the spark plug cables with 7 windings wire around the spark cable picking up a inductive pulse.
You can switch the inductions parallel,
Some RPM gauges and fuel electronics can work wit that inductive signal.
Never tried it in a Murena.

[northmurena]

Hej Hans,

perhaps this can help ? ; http://shop.alfisti.net/Tuning-Styling/Alfa-164/Elektrik-Analyse/Digitaler-Tacho-Signalwandler::3466.html

It is made for speedometer but also for rev-counter and can be configurated.

Best regards
Kai