EDIS TACH Driver Trick

[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!!!!!