Board logo

megasquirt Tacho
Valtra - 8/3/14 at 07:41 PM

What was going to be a winter project enters it's second year but the last six months have been mainly overheating issues that were waiting to pounce anyway. I'm gradualy changing everything it seems as about the only item not changed is the fan .....which now won't work either .....curses , but hey we can solve that .

Just trying to get the old Fiat Tacho to respond to the ford Edis coil and used the triple diode fix, but there's still no more than a flicker from the Mirrafiori needle, is there anything I could have cocked up? cooked diode? (how do I test ?).

Or is there an alternative fix ?

Cheers

big-vee-twin - 9/3/14 at 09:37 AM

I would connect the input of your tacho directly to one of the coil connections to check that it works, it will just read incorrectly.

If it works check your diodes to see if they are ok. Or the right way round.

dave_424 - 9/3/14 at 11:32 AM

I used my fast idle output to drive my ZX9 clocks, very easy to configure and wire in.

Dave

Valtra - 9/3/14 at 11:57 AM

quote:
Originally posted by big-vee-twin
I would connect the input of your tacho directly to one of the coil connections to check that it works, it will just read incorrectly.

If it works check your diodes to see if they are ok. Or the right way round.



Thanks , yes did consider just one coil direct but ran out of time until next weekend . Cheers

Valtra - 9/3/14 at 12:00 PM

quote:
Originally posted by dave_424
I used my fast idle output to drive my ZX9 clocks, very easy to configure and wire in.

Dave



Thanks , could be ok but bear in mind my clocks are from a 1981 fiat i.e "The dark ages"

dave_424 - 9/3/14 at 05:29 PM

quote:
Originally posted by Valtra
quote:
Originally posted by dave_424
I used my fast idle output to drive my ZX9 clocks, very easy to configure and wire in.

Dave



Thanks , could be ok but bear in mind my clocks are from a 1981 fiat i.e "The dark ages"


Should still work, I expect your tacho is expecting a pulsed 12v signal, don't know if your MS will have that output since you are using EDIS to drive the coils and not using the MS to do it like me.

old_timbo - 10/3/14 at 12:12 AM

I drive my old Smiths Tacho (from a Triumph Dolomite) off the PIP signal from the EDIS. The PIP signal is pulsed 12V and you get 4 pulses per rev on an EDIS4 as per a 4 cylinder dissy. Doesn't seem to affect the EDIS system in anyway. I tried the diode set-up and got it to read OK up to 3000 rpm after which the needle fell to zero until the revs dropped again.

Valtra - 17/3/14 at 12:40 AM

quote:
Originally posted by old_timbo
I drive my old Smiths Tacho (from a Triumph Dolomite) off the PIP signal from the EDIS. The PIP signal is pulsed 12V and you get 4 pulses per rev on an EDIS4 as per a 4 cylinder dissy. Doesn't seem to affect the EDIS system in anyway. I tried the diode set-up and got it to read OK up to 3000 rpm after which the needle fell to zero until the revs dropped again.



Tried the tacho direct from one coil pack and it works (reading low of course) but it sounds like it may be worth trying your pip signal method , has anybody got any dire warnings why I shouldn't ? I presume it's just a case of piggy backing from the relayboard where the pip signal enters (Tach) ??????

Valtra - 20/3/14 at 01:36 PM

bump

Valtra - 30/3/14 at 08:37 PM

Ok tried to use the pip signal from the relay board and not so much as a flicker . So now I've re-done the diode fix including a resistor from centre to earth ( not too confident about the resistor's orientation or even if it's important) was more carefull not to cook the diodes and this time I do get a flicker but not anything acurate consistant or usefull

Just wondering if it's time to cut-and-run and source a different tacho that will accept a signal from either the microsquirt/relay board or the edis module . Any sugestions ?

BaileyPerformance - 30/3/14 at 09:01 PM

The diode method is a bad idea, we have seen this cause misfires.
Try pin 2 on the EDIS, is no luck try pin 11.

If still no luck we can modify your tacho to operate on the low voltage output from the EDIS pins or direct from the megasquirt.
Factory tacho's in older cars (single coil) are triggered by the fly back from the coil, this is minimum 50v (can be as high as 500v) not 12v. Normally it's quite simple to modify the tacho to operate on 5-12v.

Valtra - 30/3/14 at 09:26 PM

Thanks for the response , I must admit the diode method looks a bit "Heath Robinson" at best. I've tried pin 2 from the Edis but not 11 , could be worth a shot . If not probably just make do with a simple digital readout from a ht lead sensor.

Incidentaly I'm thinking of getting my car set up properly by yourselves , do you have any available days in April ? please message me with details.
Ian

BaileyPerformance - 30/3/14 at 10:12 PM

We would love to map your car :-) will check diary and msg you with some dates.

We can probably sort your tacho when you come for the mapping session, included in the price.

dave_424 - 30/3/14 at 10:18 PM

Like I said before, if your tacho is looking for a pulsed 12v signal like it being connected to a coilpack then use the fast idle output from megasquirt just connect the wire from your tacho to that output then in tunerstudio go to tacho and configure it there

BaileyPerformance - 30/3/14 at 10:57 PM

quote:
Originally posted by dave_424
Like I said before, if your tacho is looking for a pulsed 12v signal like it being connected to a coilpack then use the fast idle output from megasquirt just connect the wire from your tacho to that output then in tunerstudio go to tacho and configure it there


Most early type tacho's are NOT triggered by a positive 12v signal, it's the much higher fly back from the coil that triggers. So, if the tacho was not triggered by the EDIS pin 2 or 11 the likelihood is it won't work with a 12v output from the MS.

Modern tacho's (such as Stack) will work with almost any input, later production car tacho's (including bike) are triggered directly from the ECU (5-14v)

scudderfish - 31/3/14 at 08:54 AM

I once got my tacho working by using the flyback from a relay coil. It worked, but the noise of the buzzing relay behind the dash meant I binned it as an idea pretty quickly.

matt_gsxr - 31/3/14 at 09:02 AM

As above. My tacho (Aprilia 250 FWIW) wouldn't work from 12v switched so I put a small transformer (from a camera flash) and a couple of resistors in series.

This gave the same kind of high voltage kick that you get from the coils.

Can't remember the exact circuit or claim that it was designed.

It has worked for the last 6 years.

Valtra - 7/4/14 at 12:22 AM

Thanks for all your input guys . may just end up with a cheepo digital readout for now though analogue is way better for a tacho or wait for Stoneleigh and rummage.

I have got an old Tim Tacho somewhere from my first car (1.1Fiesta Pop Plus ) but as that was bought in 1982 probably no better than the fiat clock