Dougy Posted March 1, 2021 Report Share Posted March 1, 2021 After some advice with the atom g4x and high voltage tacho. The tacho is the factory one in a Suzuki Vitara, running a 20v4age engine, atom g4x ecu, cop setup. I've got the tacho running off of the ignition #4 output. Initially I removed the resistor in the tacho (46k) and swapped this for a 1k resistor. I then taped the ecu aux output into the factory tacho signal wire (used to come from the ignitor). The tacho wouldn't read. After a lot of trial and error I've got the tacho to work, but hoping to get some opinions if this is correct. Currently, the ecu output is taped into the tacho signal wire under the dash, also on that same tacho wire is now a relay coil, the tacho wire is connected to pin 85, and a 12v ignition feed is connected to the 85pin (coming from the old ignitor 12v supply). This makes the tacho work. Another way that works is by removing that relay and just plugging the factory ignitor back in (ignitor is doing nothing anymore). I would have thought that the ECU signal alone, taped into the tacho signal wire, with the resistor changed inside the tacho would be enough? Or does it also need that 12v feed supplied on the same wire? Wouldn't this back feed to the ecu? Hopefully that makes sense. Thanks Quote Link to comment Share on other sites More sharing options...
Adamw Posted March 1, 2021 Report Share Posted March 1, 2021 The ignition outputs are only pulled up to about 6V so your tacho may want more than that. You could try a 1kohm pull-up resistor connected to 12V. Or if you have an aux output you can swap with the ignition output, as they are already pulled up to 12V. Quote Link to comment Share on other sites More sharing options...
Dougy Posted March 1, 2021 Author Report Share Posted March 1, 2021 Thanks for the reply Adam. I have replaced the 46k resistor in the back of the tacho to a 1k, which made no difference. I can get it to work how it is at the moment, (tach output from ignition output 4 to tacho signal wire, also spliced into that tacho wire is a relay coil attached to pin 85, and a 12v ignition switched feed to the pin 86. It also works if I removed the relay and added a resistor from 1k upto 67k. Does that sound correct? Quote Link to comment Share on other sites More sharing options...
Adamw Posted March 1, 2021 Report Share Posted March 1, 2021 30 minutes ago, Dougy said: It also works if I removed the relay and added a resistor from 1k That is what I said, that is a pull-up. Your relay coil and the ignitor were effectively just working as a pull-up. If you move your tach wire to one of the proper aux outs you wont need the pull-up Quote Link to comment Share on other sites More sharing options...
Dougy Posted March 1, 2021 Author Report Share Posted March 1, 2021 Is it fine to keep running it from the ign output? All other aux outputs are in use Thanks for the help Quote Link to comment Share on other sites More sharing options...
Adamw Posted March 1, 2021 Report Share Posted March 1, 2021 9 hours ago, Dougy said: Is it fine to keep running it from the ign output? If it is working, yes. 9 hours ago, Dougy said: All other aux outputs are in use But surely you can move something like your fan or fuel pump wire to the ignition output to give the tach a proper aux? You can move pins without even any tools required. Quote Link to comment Share on other sites More sharing options...
Dougy Posted March 2, 2021 Author Report Share Posted March 2, 2021 Sorted. Moved to aux 3 and moved FP to ignition 4. Tacho works with no pull up needed. Just need to calibrate as doesn't read correctly Thanks for the help Quote Link to comment Share on other sites More sharing options...
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