Help with building your Speeduino, installing it, getting it to run etc.
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You certainly could try it, but the quickest solution (in my experience) is to first determine the type of signal the tachometer needs (or used to receive), and configure Speeduino to supply that type of signal.
By Svetoslav
Originally the ECU had an signal wire that went both to the tachometer and the negative lead of the ignition coil.
So I guess I need a negative signal of some sort?
wWC5i6QqPI.png (139.71 KiB) Viewed 720 times
By dazq
Svetoslav wrote: Fri May 10, 2024 5:20 am Originally the ECU had an signal wire that went both to the tachometer and the negative lead of the ignition coil.
So I guess I need a negative signal of some sort?

It's not a negative signal .
These sort of tacho trigger either from the switching of the gnd or most commonly from the back emf pulse from when the coil is switched off.
You can recreate the back emf signal using a relay or similar coil ( you can remove the mechanical guts you only need the coil though leave the metal core in the coil else it won't make the back emf pulse) .
Some experiments may be needed to determine if one coil will be enough to trigger the tacho.
By Svetoslav
I did try a circuit with a relay coil and transistor, but didn't work.
HiVTacho.gif (6.37 KiB) Viewed 701 times

Or you mean to wire the coil inline with the tach signal wire?
By dazq
Yes that's the sort of circuit .
As I said some experiment will be needed .
Depending on the relay will give different amounts of back emf pulse. I once had to use an old fuel injector to get sufficient pulse to make the OEM tacho read correctly, multiple relay coils also can work.
Just make sure the relay you use doesn't have any diode installed inside like many vehicle relays do as that will kill the pulse.
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+1, cutting the diode or resistor out of the relay will increase the pulse amplitude. I always cut them out. If no joy, use a larger or lower-impedance inductor (injector, bigger solenoid, etc). Verify your transistor VCEO is rated at least 150V with no internal body diode (same problem as inductor diode shorting the pulse).
By Svetoslav
I'll figure out the tach eventually, but now there is another issue. I connected the ignition coil wrong and swapped the 12v and gnd. that caused a short and after that when I fixed it, I didn't have ignition. I thought the coil is dead so I got a new one, but no, I still dont have ignition.
Everything else is working, in test mode the injectors are working, but not the ignition channels. I even tried the 4th channel, which was not used before and it's not working.
Can you give me advice what should I do? I checked the wiring to the coil and it's fine. Is the arduino bad or the speedo board itself? The LEDs for the ignition are blinking, but only two and the same on all channels which seems weird.
By Svetoslav
Tried it again today. No spark. The coil is wired correctly. In test mode the LEDs for the ignition channels are blinking normally, but with them also Led1 blinks which is for the injectors. Is this normal?
I have another arduino which I can swap to test. Is it worth trying?
Please advise.
By Svetoslav
Ignore my previous posts, I'm an idiot. Turns out the 12v wire was damaged and couldn't supply enough current for the coil. Changed the wire with a thicker one and fixed the issue.

Now the car starts but wont idle without throttle.
I checked the timing with timing light and got it spot on.
So I'm using a 2 wire Bosch ICV. Set the pwm at 100hz, it is humming but not open and it doesnt move when the engine got up to temp. Tried setting it to reversed, which made it fully open, the engine is idling high at 1500 rpm, but still the valve stays open and doesnt move when it gets warm.
Heard people with the same icv's pitting diode between the icv pins. Do you think I need one too?
So can anyone help with that?
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I test valves to find best values. With engine off, I set 50% DC and change Hz. Once I find best response to Hz, I find the lower and upper DC range. Note some PWM valves (especially rotating barrel valves) will have high-idle airflow when off (limp-home mode), close with added DC, then re-open.

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