Tacho output - Megasquirt

[SorenDK]

Hi

I'm seeking advice from you guys on how to get my tach working in my 1974. The case is this:

I have a '74 coupe with a '77 engine - instruments in dash are original 1974, engine has been replaceI'm d sometime in the past by PO.
I have restored/upgraded engine with megasquirt 2/V3 so its running fuel and ignition via 36-1 trigger/VE sensor and wasted spark via a logic coil from a VW golf VR6.

All is fine - except the tach - the signal out from the MS box does not work with my 1974 tach.
I'm sure some of you have experienced the same - and maybe solved this? I know ashlocktech are selling an adapter but is there an easy fix like the one in pic? Have any of you tried building and applying this ?




Thanks from Søren

By the way - here is a pic of my car...

[pampadori]

Does the MS allow you to program the lowside tacho output? That is to say, modify how many pulses per revolution? That's how the AEM works but I'm not familiar with the MS.

[targa44]

Soren,

Long story short...... IAC1A to adapter to tach. Have you asked the question to the MSextra forum group? Sorry, I haven't tried it YET - but I'm using a relay board MS3 V3. I just purchased the Ashlock (Tach-Adapt) you mention.

good luck,

[jpnovak]

The standard PWM tach signal will work with a 74 tach. I have done 2 EFI installs doing this configuration. These normally trigger from the standard points opening.

So... Do you have your MS2 configured in SW and HW? Have you connected a jumper wire from your programmed output pin to the Tachout wire location? You can't just plug it in without connecting internal to the ECU circuit.

[CarreraEvo]

Sorry to hijack the thread, but it seems Soren got it sorted.

I have a very similar problem:
Porsche 911 Carrera US 1974, MS2 V3.0, ITBs, dual COP, cam sensor.

I jumpered JS0(IAC1) to IGN and enabled Tacho Output in TS -> IAC1.
I've checked that there's connection from JS0 all the way to the black/purple wire on the tacho.

The tacho was working before I started installing the MS2.

But now it's not working

Any suggestions??

Here's a few pictures of my project:
https://www.instagram.com/carreraevo/

ITBs are JSR

[edc153]

Ok, I have a similar problem. The schematic shown above does not tell us what
"From MS2" is connected from. I cannot use the IAC ports due to using stepper idle.
All we really need to know is which board port provides a pulsed 0-12v signal, isolated enough to use for the TACH. If we have that, then creating the above shown circuit is simple.
So yea,,,
What is "From MSII" referring to on that page?
This assumes the porsche tach is 0-12v pulsed, which some may not be.

Originally Posted by CarreraEvo

Sorry to hijack the thread, but it seems Soren got it sorted.

I have a very similar problem:
Porsche 911 Carrera US 1974, MS2 V3.0, ITBs, dual COP, cam sensor.

I jumpered JS0(IAC1) to IGN and enabled Tacho Output in TS -> IAC1.
I've checked that there's connection from JS0 all the way to the black/purple wire on the tacho.

The tacho was working before I started installing the MS2.

But now it's not working

Any suggestions??

Here's a few pictures of my project:
https://www.instagram.com/carreraevo/

ITBs are JSR

[dap930]

edc123,

What you have to do is figure out which "tacho" port you are going to use from the MS2 CPU, JS10, JS11, etc. that you will select in TS. Then you have build the interface circuit shown above in the proto area of the V3.0 circuit board, which is the 12VDC pullup circuit. Connect a jumper wire from JS10, JS11, etc. pad to the input of the 12VDC pullup circuit. Then determine which output pin on MS2 40 pin connector you going to use; IGN pad for pin 36, SPR1, 2, 3, 4 for pins 6, 5, 4, or 3. Connect a jumper wire from the output of the 12VDC pullup circuit to which ever pad (connector pin) you are going to use.

[edc153]

FYI, My board is wired 6 channel IGBT for twin plug, so there are 12 IGBT to fire
12 COP coils.
Optical trigger from nissan opti sensor w DIY autotune opti wheel. This board has more stuff going on than any other MS2 setup can have.

It is on a running engine, but no tach signal.

The answer to,"where is MS2?" on the board question is: JS10 in my case!
Why could'nt they just tell us to wire the center pin of the 2n2222a to that point.
What you are also defining is that (S12) is +12v but not 12v pulsed.

I could deduce that from the nature of an NPN ic, but not definitely, because I may have no idea which location is pulsed 12.

Thank you for your reply.

Originally Posted by dap930

edc123,

What you have to do is figure out which "tacho" port you are going to use from the MS2 CPU, JS10, JS11, etc. that you will select in TS. Then you have build the interface circuit shown above in the proto area of the V3.0 circuit board, which is the 12VDC pullup circuit. Connect a jumper wire from JS10, JS11, etc. pad to the input of the 12VDC pullup circuit. Then determine which output pin on MS2 40 pin connector you going to use; IGN pad for pin 36, SPR1, 2, 3, 4 for pins 6, 5, 4, or 3. Connect a jumper wire from the output of the 12VDC pullup circuit to which ever pad (connector pin) you are going to use.

[edc153]

Because this is a 6 igbt coil output installation, all of the normal potentially available points to extract a tach signal from are not available. In tunerstudio, all are dedicated for an individual 1/3 rotation spark trigger. Unless you have a tach with a 3cyl setting, it cannot work. The stock tach needs 6 individual pulses for 720*.

The above shown pullup circuit cannot work, unless you build 6 of them, one for each coil trigger, to output on one pin.

DiyAutotune initially directed me to the above pullup circuit; apparently missing the fact my board was wired for 6 channel spark.

I bounced it off them again, and was given the image showing the use of individual diodes for each channel leading to one Zener then to output pin"X".

When the parts arrive, I will build and post the results...

Originally Posted by dap930

edc123,

What you have to do is figure out which "tacho" port you are going to use from the MS2 CPU, JS10, JS11, etc. that you will select in TS. Then you have build the interface circuit shown above in the proto area of the V3.0 circuit board, which is the 12VDC pullup circuit. Connect a jumper wire from JS10, JS11, etc. pad to the input of the 12VDC pullup circuit. Then determine which output pin on MS2 40 pin connector you going to use; IGN pad for pin 36, SPR1, 2, 3, 4 for pins 6, 5, 4, or 3. Connect a jumper wire from the output of the 12VDC pullup circuit to which ever pad (connector pin) you are going to use.