I lost my tacho when switching to coils.

[LowR3V'in]

Hello.
You may have seen this on a dead forum I posted on but I hope for
better luck here. :up:

My MS is a plug and play I bought off a forum member so I don't know exactly how it's hooked up but it worked.

When switching to coils. The "smart" ones. I lost signal to my tacho.
Is there a setting or do I need to rewire it? Anyone have a clue?
I used those wires as the signals. Normally l.e.ds go there.






These are the coils.

https://www.diyautotune.com/product/ign-1a-race-coil/

[LowR3V'in]

This is the msq and log.

https://drive.google.com/open?id=0BzS8yr8ffWPudkRYYkhhcGdZdzQ

[varg]

When I opened your MSQ tach output was switched to 'off'

[LowR3V'in]

i switched it off when it didn't work so switching it on did nothing.

[varg]

Might have said that to begin with.

It's set to JS10, what hardware changes did you make? Did you alter anything post JS10? I imagine JS10 was just jumped right to a spare output pin.

[LowR3V'in]

I changed nothing. Just took the leds out and soldered in the wires for the coils.

I'm going to tear it out and do my own research nobody seems to know what to do. kinda worrying.:???:

[varg]

Double check the hardware, make sure you didn't accidentally disconnect something or bridge a connection. I don't see any software settings that would cause this.

[kyleconstantine]

Hey is the car running alright otherwise? When i wired in coils to my old ms i didnt have to remove the LEDs. Im pretty sure i was going from the resisters next to them. (This was my old ms, im on microaquirt now) maybe taking out the leds interupted a sigal from going back to the tach output?

[varg]

The circuit for the LEDs being what it is, removing them should have no impact on the function of the unit in this case. They're turned on by the NPN transistors Q6-8, which are switched by energizing the base, which is directly connected to a pin on the CPU. OP's mod is using Q6-8 to trigger the internal high current transistors in the coils, so it's not like the Q6-8 are unloaded or anything.

As for the tach output, as long as the tach output JS10 is correct (connected directly to pin 17 of the ECU), JS10 should be jumpered directly to whichever output pin which corresponds with pin 6 on the Motronic. Unless the builder of the megasquirt put some tach driver circuit between JS10 and the pin. The CPU pins can drive the tach directly as it only requires 'logic level' 5V square wave input - I'm driving the tach directly off of JS0 with my megasquirt. It's conceivable that JS10 is wrong, and that it got changed from whatever it was intended to be by the builder when changing the tune to suit the new coil setup.

[LowR3V'in]

Yeah idk I bought it as a plug and play like 10 years ago

So there should be a wire from j10 to #6 on the harness with no circuit in the middle
i'll check that out, thanks.

No it just stopped working when I replaced those l.e.ds with a wire to the coils.
Just clicked "wasted spark" bam. done..

[LowR3V'in]

#6 is jumped to #1 in the motronic harness.
and that goes #2 on the megasquirt harness.

on the motronic side #1 is "ignition pulse to final stage"
Does that mean it was for little thing around the stock ign wire?
I can just take that off yes?

[LowR3V'in]

#2 on megasquirt goes directly to ign. No wire. Just the metal shit in the board itself running to "ign".

"j10 (ign)" is unused so i'm going to run a wire from that to other "ign".

Hope my shit don't blow up. ;D


so how the hell was I getting signal to my tach to begin with?

[LowR3V'in]

I jumped j10 to ign that goes to pin for the tach.

It works sorta. at 2,000rpms the tach read about 500rpm.
At least it's moving but what's the problem you think now?

[varg]

JS10 (ign) should go directly to whatever interfaces with pin 6 on the harness, whether that be a DB37 pin which follows an adapter to 6 or a direct connection to 6. Anything else connected to motronic pin 6 should then be disconnected.

Motronic pins;
Pin 2 is a ground from the ECU to the chassis
Pin 1 the ground from the coil primary - the ECU opens and closes this ground to fire the coil

Megasquirt pins:
Pin 2 is to be connected to the crank position sensor shield
IGN on the DB37 side of the board goes directly to pin 36 of the DB37.

If pin 36 on the DB37 leads to pin 6 on the motronic, then you'd want to do this (the yellow wire, ignore all else):


If the tach connection on pin 6 (motronic) was connected directly to pin 2 (motronic) then the tach must have been functioning the old school way - picking up pulses on the coil ground. I've never tried it but I guess it might have worked, but the tach is expecting 5V pulses.

If all of this agrees with what you've done, then the tach should work fine.

[LowR3V'in]

I see I see. So my shit was "the old school way". It worked perfectly btw.

I did the yellow wire thing. js10 to ign.

So I just need to rewire #36 on the megasquirt to go to tach on the motronic harness.
Thanks.