MSefi.com read only forum (Jan.15,2018)

Hello

I read from http://www.DIYAutoTune.com/tech_article ... led_vw.htm MegaSquirt-II PCBv3.0 Mods Required. And there is that you'll need a 1K pull-up resistor from the 5 volts in the proto area to TachSelect but there is no such thing mentioned in megamanual assembly guide for the V3 main board. So which way is the right way?

ignasio,

Some Hall sensors have the pull-up built in, others do not. It seems the DIYAutoTune has determined that your sensor (for a water cooled VW, according to the link) does not have a pull-up, so they suggest you add it.

Lance.

IIRC, it depends on the hall effect sensor. Some are three wire types which take +12v and ground with an output - that wouldn't need the pull up resistor. Two wire types likely would.

My hall sensor have three wires so the megamanual circuit is ok no need for extra resistor. Thanks for responding.

Ignasio,

All Hall resistors have 3 wires - power, ground, and signal - plus possibly a shield wire for the harness. It is VR sensors that have 2 wires.

So having 3 wires is no indication of whether you need a pull-up or not (though if you are following DIY's guide and it applies to your vehicle, then I suspect you do need a pull-up - they don't just make that stuff up!).

If the Hall sensor already has a pull-up, then you will consistently find a significant voltage (usually 5, 8, or 12V) on the signal at some point in the rotation of the wheel while the sensor is powered up. If the sensor does not have an internal pull-up, the signal will "float" near ground, and likely remain fairly low (generally under 1 Volt, and it won't depend in the crank wheel position).

Lance.

Actually, I have Audi but DIYAutoTune don't cover it. Audi and VW engines and electric systems are basically the same, the older models at least were. Thanks for explaining now I know how to proceed.