EDIS TACH Driver Trick

[Jim]

A TACH Trick for EDIS users :
The output from the EDIS module ( PIP ) to MS will directly drive a
power MOSFET or IGBT ,
(Metal Oxide Semiconductor Field Effect Transistor) or
(Isolated Gate Bipolar Transistor)
either one of these types of transistors put virtually no load on
whatever is driving them and their outputs handle lots of power .
( unfortunately their "Gate" input is easily destroyed by
the slightest static charge on your body or tools, make sure the gate
has at least a 100K or less resistor to ground , do not let it float ,
keep a small strand of wire wrapped around the pins until
it's soldered into place )

This enables you to create a TACH Output without the very questionable
and dangerous Diodes connected to the Ignition Coils !!!

I use the output of the "Opto" circuit to drive not only MS , but also an
International Rectifier #IRF540 "HexFet" MosFet power transistor
with a 2 watt 680 ohm pull up resistor to provide a
perfect 12 volt square wave output for my Tach (with NO spikes) .

Works great .

[Anders Karlsson]

MSnS-EDIS, V2 board, extracode 021u3 on a 4 cyl Opel engine.
Sounds like the solution to my problems with my Autometer tacho.
The tacho needle jiggles very much at idle, and the tacho shows a lower value than the tacho in Megatune.
I noticed that the Autometer stabilized and showed more reliable values when i turned on the lights and some other electric stuff in the car. First i thougt the alternator was bad, because i have 15 V right after start, but thats because the battery needs charging of course.
The tacho doesn´t stabilize after some time of running however, so i guess the signal voltage is too high or too noisy.
I will change the voltage control unit in the alternator first, and see if it makes any difference.
Is there any schematics or pictures on where to connect the MOSFET/IGBT?
I didn´t quite understand where to connect it.

[EstateAgent]

Why would the diodes be 'questionable and dangerous'?

They dont touch the HT side of things, they just passively tie onto the switched ground side of the coils.

Many many tacho's tie direct to the switched ground directly! So if its dangerous, theres certainly a few million cars we should stay away from! (Even Fords using the EDIS!)

[Jim]

If you have ever used an ocilloscope to look at what goes on ,
even on the primary side of the coil , the trash and spikes would
astound you , it's not really "dangerous" to you , but to
semiconductors it can be instant death just waiting to happen ,
most Tachs have built-in resistor and capacitor filtering networks
as well as Zener clamp diodes to prevent frying the chip .

Why would you want to attach a wire carrying this type of trash
to your precious MegaSquirt ECU ? where if some how, some way,
this trash got into the wrong place on your board it could
instantly fry it ?

To Me , that's a risk I would like to avoid .
Therefore I call it "dangerous"

And that's not all , connecting a wire to the coil acts as an antenna
broadcasting noise into the air , maybe it will get into your stereo
and maybe not , (try tuning in a weak AM radio Station) ,
I'd rather not have one more thing that needs to be shielded or filtered .

By the way , just for kicks , try this :
put your left finger on a grounded screw or bolt on your car and
take your right finger and touch your "Tach" wire ,
IT'S ONLY 12 volts it can't hurt you !!!

[Jim]

To Anders :
I'm sorry I can't give you specific instructions on were to
"tap into" your MS board because I use the new Version 3 board .

However I can provide more info on how it can be done .
First , basic information :

On the V-3 Board there are 2 separate stand-alone curcuits for
the Tach Input , one of them is designed for use with a direct input
from a "Variable Reluctance" or VR pick-up coil inside some
electronic distributors , the other curcuit is called "Opto" which is
short for Opto Isolator (Optically isolated transistor) , it's purpose
is to isolate MS from the trashy noisy signal that you get when
wiring straight to the primary of an Ignition Coil , this is also the
curcuit recomended for use with the PIP Signal coming from
an EDIS Ignition control unit .
One of these 2 circuits must be selected by soldering jumpers on the
printed curcuit board , one jumper for the input to the curcuit from
the DB-37 connector and one jumper on the output which goes to the
MS Chip for it's "tach" input .

You may "tap into" the PIP signal from EDIS before it gets to MS or
after it goes through the "Opto" conditioning circuit .

I chose to tap into the signal after the Opto circuit because it was
easy to do while I was wiring my board and because the output of
the Opto Curcuit was a known quanity , I could look at the schematics
of the circuit and see that it would not be a problem to drive an
additional load from it .
However , I am reasonably confident that the PIP output of the
EDIS unit could also drive an additional load , provided that the
load was only the Gate Input of a MOSFET or IGBT transistor .
These types of transistors have an input that acts just like a very
small capacitor , they have an almost infinite input resistance , so
tapping on one of these transistors is almost the same as simply
adding a very small capacitor to ground .

Here's how to do it : (See the attached Picture)

Also , if anything starts working or stops working when you
turn something else on or off , you need to start looking at your grounds
ALL OF THEM , if you can avoid it , never use the car body as a ground .
Run a separate ground wire from the battery or engine block .
The very best setup for grounds is to have them ALL go to the same
point .
The Engine Block is the best place .
Also make sure that you have a BATTERY CABLE from your
Engine Block to the Body .

[tony2ltr]

Can't you use pin 2 on the edis for tach input?

[sevenDriver]

I have connect the tach to pin 11 of my EDIS4 module.

EDIS4 Pin 2 is the EDM = E-DIS Diagnostic Monitor signal.

[EstateAgent]

If you have ever used an ocilloscope to look at what goes on ,
even on the primary side of the coil , the trash and spikes would
astound you , it's not really "dangerous" to you , but to
semiconductors it can be instant death just waiting to happen ,
most Tachs have built-in resistor and capacitor filtering networks
as well as Zener clamp diodes to prevent frying the chip .

Why would you want to attach a wire carrying this type of trash
to your precious MegaSquirt ECU ? where if some how, some way,
this trash got into the wrong place on your board it could
instantly fry it ?

To Me , that's a risk I would like to avoid .
Therefore I call it "dangerous"

And that's not all , connecting a wire to the coil acts as an antenna
broadcasting noise into the air , maybe it will get into your stereo
and maybe not , (try tuning in a weak AM radio Station) ,
I'd rather not have one more thing that needs to be shielded or filtered .

By the way , just for kicks , try this :
put your left finger on a grounded screw or bolt on your car and
take your right finger and touch your "Tach" wire ,
IT'S ONLY 12 volts it can't hurt you !!!

But your not connecting those lines to the MS anyway. The only lines the MS use are PIP and SAW.
And like you saw, Tacho's have circuitry to suppress the spikes.

I can see your point about it being a good way to suppress noise, though using Fords suppressors in the places they put them never has interfered with the radios on my cars at least.

[tony2ltr]

Sevendriver, are you just going straight to the tach from pin 11? or are you using the diode and zener setup? I have some of the EDIS instructions printed out and it says to try pin 2 from the EDIS 4 right to the tach. I haven't fired the engine yet, but is this going to work?

[Anders Karlsson]

Great explanation...

Thank´s a lot! Now i understand.

[Jim]

To: Tony2ltr and/or Sevendriver

All EDIS Modules have an output called IDM , it's always pin-2 ,
this is a specialized output for comunicating with the Ford ECU .

It may or may not work depending on your Tachs input requirements .

I would never recomend connecting a Tach directly to your EDIS .

Here's why , the chip inside the EDIS that creates the output on pin-2
was designed to have a specific type of load attached to it and your
Tach has capacitors , resistors and diodes making up it's "Input Filter"
this filter may overload the output of the EDIS and smoke either
just the specific output you are connecting to or the entire Module ,
or it could even work OK , but cause the module to act strange or cut out
or who knows what .
It's better to play it safe and put as small of a load on these outputs as possible ,
which my circuit does , my cicuit also provides exactly what
ANY Tach wants to see on it's input , Plus 12volts or Ground .
I know that my cucuit works perfectly using the PIP Output .

4 cylinder EDIS modules have an output called CTO (Clean Tach Out) ,
I don't know anything about this output as far as directly driving a Tach ,
ALL of the EDIS signal outputs are designed to connect directly to the
Ford ECU , the ECU then provides outputs to other parts like the stock Tach .
I would imagine , because of it's name , that my circuit should work fine with this output ,
but I'm just guessing , I know it works with the PIP Output .

Here's some more info on EDIS :
http://www.dainst.com/info/edis/edis.html

Here's a quote copied from that page :

The IDM signal present on all EDIS modules is used as the factory tach output to the ECU.
This signal is used to determine the welfare of the ignition system.
If a coil primary opens or does not fire, the IDM signal is not emitted,
and thus the coil is faulty.
The IDM signal is triggered by the flyback voltage of the coil being fired.
The EDIS module processes this into a 512us pulse on the IDM line during operation.
When the engine is stopped, but the Key is turned on (KOEOff),
the EDIS module emits a 64us pulse every 262.144ms to indicate proper operation.
Because of this, any tachometer operation from this line must filter out the 64us pulses.

I hope this helps

[sevenDriver]

@tony2ltr
I have connected the tach directly to pin 11 from the EDIS4 module and this works without any problem.

@Jim

4 cylinder EDIS modules have an output called CTO (Clean Tach Out) ,
I don't know anything about this output as far as directly driving a Tach ,
ALL of the EDIS signal outputs are designed to connect directly to the
Ford ECU , the ECU then provides outputs to other parts like the stock Tach.

In old Escorts (EEC-IV with external EDIS4) the tach is also directly connected to pin 11 of the EDIS4 module. In newer EEC-IV (with integrated EDIS) the tach is connected to pin 4 of the ECU.

[tony2ltr]

Well, It looks like I have some rewiring to do then.

Thanks gents

[Anders Karlsson]

It works! The Autometer tach now shows (almost) the same value as the tach in Megatune. However, i trust the Autometer to be more accurate, since the MT tach has a resolution of 100 rpm.
When the MT tach shows 1000 rpm the Autometer shows something like 1020 rpm or so, and ill rather be safe than sorry.
I made my first test drive this monday by the way, the engine runs on req-fuel settings and maximum boost of 0,3 bar. Runs rather rich, so now there is some tuning to do!

[tony2ltr]

Which Works? The pin 11 output?

Tony

[460stang]

Pin 11 works on my EDIS 8 and drives a stock ford tach or a Autogauge monster tach.

On my EDIS 4 Pin 11 or pin 2 (CTO) will not drive my Autometer tach.

[Anders Karlsson]

Which Works? The pin 11 output?

Tony

I made the "trick" with the transistor shown above. It uses the PIP-signal, wich i take out on pin 29 on the DB37 connector, then to the relay board.
Works fine.

[tony2ltr]

Great, Maybe I'll try that then, I am not far enough with my project to know if it works yet. LOTS OF WIRES!!!!!

[tony2ltr]

Great, Maybe I'll try that then, I am not far enough with my project to know if it works yet. LOTS OF WIRES!!!!!