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Sierra Tacho
stargoaly - 10/9/14 at 07:49 PM

Anybody out there help?

Have been building this thing for 10 years (Busy job). First build as well. Finally started it and it runs like a dream. Now preparing for IVA. However I have a small problem knowing how to get the tacho working. I have a 2 litre silver top mondeo running of an early non PATS ECU. Everything else on the car has been taken from a donor Sierra including the instrument cluster. On the sierra the feed to the tacho came from -ve on the coil however there is no such connection on the Mondeo engine wiring loom (I did connect to tacho output from ECU with no joy) so I was going to splice the feed to the tacho onto one of the output wires from the coil pack to the ECU and see if that worked. Has anybody ever tried this and did it work.

Any advice will be gratefully received.

Thanks
Dave

avagolen - 11/9/14 at 07:17 PM

Hi Dave,
I do not know exactly the signal requirements
but maybe it can be sorted with a few checks.
Do you have a volt meter?
If you run the engine and check the signal from the ecu.
If you connect the meter between ground and the signal and you
get a voltage greater than zero or if you connect it between
12V and the signal and get a voltage, this information can help
solve your problem. Please ensure you get your voltmeter
the correct way around....
I am away from internet most of the time. I will respond
when I can

Post your results here. If neither gives a voltage it may need a
resistor to + or - for an opencollector cct.

big_wasa - 11/9/14 at 09:16 PM

The signal from the oem ecu works with the after market tacho but I've never tried with the sierra dash.

If you just hook on to the coil pack on the zetec, being wasted spark the rpm will be half that of a points system or the ecu output.

whitestu - 12/9/14 at 07:02 AM

quote:

The signal from the oem ecu works with the after market tacho but I've never tried with the sierra dash.

If you just hook on to the coil pack on the zetec, being wasted spark the rpm will be half that of a points system or the ecu output.


If it works at half rpm from one of the coil pack feeds it may be possible to connect the tacho to both feeds with a couple of Zener diodes to get a full reading.

Does the tacho definitely work?

Stu

[Edited on 12/9/14 by whitestu]

stargoaly - 14/9/14 at 09:14 PM

Thanks to every one for their replies. Wife got me decorating all weekend when there are more important things to do.

Stu, Tacho worked when I removed it from the donor car, however I do have another I can try.

I'm going to try the things suggested this week sometime. Again thanks for your thoughts.

Dave

Non custom - 26/9/14 at 07:12 PM

This is the diode mod done on cosworths to solve the same issue when using wasted spark setup on them may help I don't know ??

http://www.autosportlabs.net/images/1/13/Tach_circuit.jpg

stargoaly - 27/9/14 at 06:41 PM

Thanks to you all for your help.

I have ended up splicing into one of the outputs from the coil pack to the ECU and my tacho now works although it is reading half what it should do so as said earlier next stage is to splice into other and use the circuit Non Custom sent.

Many thanks again

Dave

Non custom - 28/9/14 at 09:22 PM

I beleive that mod is done at the back of the clocks for ease also stargoaly