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ATOM ECU on Honda EK9 Tachometer.


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Hi all.

I connected an ATOM as a piggy back to a Honda OEM EK9 ECU and the tachometer runs fine.

Problem starts when I disconnect the OEM ECU tacho wire and the tacho operates for about 1 sec and goes dead.

When this OEM wire is reconnected, the tacho is alive again.

I then connected a Xtreme ECU to the engine (with all wiring) and the tacho runs fine with the OEM ECU fully disconnected.

With the engine running (on ATOM), I measured the OEM tacho wire at 6.5VDC.

Pls advice.



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I would try a different aux output on the Atom and see if it still has the issue.

Also make sure the firmware is identical with the Xtreme to the Atom.

Edited by Simon
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I connected IGN 2, 3 and 4 as signal source and same outcome.

I connected another brand new ATOM and ended up with the same outcome : upon cranking and ignition of the engine, the tacho goes dead.

Firmware is of latest version.

Is there another way (or method) of making the tacho work without connecting the OEM ECU?

This car uses all standard accessories : A/C, engine fans, fuel pump, check engine light, etc.

Do you require the ATOM mapping?




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Hi Andrew,

I have emailed you a reply, but for the sake of anyone else who has a similar problem I will post the reply here also:

Hi Andrew,

I have spoken with one of our hardware engineers. The difference between the Xtreme and the Atom ECU's ignition channels is that the Xtreme has pullup resistors that are always on, where-as the Atom has a newer style of driver in which the ECU firmware controls the pull-up resistor.

Most tachos have a built in pull-up resistor, but it appears your one does not, and the OEM ECU provided the pullup resistor. The solution in this case is going to be wiring a pullup resistor into your installation. The pull-up resistor will go between the Atom's ignition drive output and an ignition switched power supply (like the one powering the Atom). We recommend a resistor value of 1000 Ohm (1K).


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