old Tach Signal hack on this Mitsubishi
The stock RPM meter has one wire towards ECU. I tried to tap it to one of injector channels, and added it to all h masks. The gauge was working properly, with two issues:
- when no free injector output channels available
- No tach signal at deacceleration (decel fuel cut => gauge shows 0 rpm at decel)
Configurable tach output can use any GenBoard/Manual/DigitalOut
You can simply connect a free
- injector output (or even the flybackless 2nd WBO2 heater output)
- or p259 output
- or stepper output
- or ignition output
But the gauge might have some input signal requirements. Lacking a datasheet, often hard to know, but some careful experimentation is usually safe.
Resistive pullup to +12V
A 270 .. 2k4 resistor pullup (to +12V) can be tried (assuming they forgot it from the RPM gauge input). Not much risks here (any output can take 12V through 270 Ohm or higher limiting resistor without damage).
Since this involves more risks to the gauge (and to you : don't touch the signal, electric shock!), you might want to try the "resistive pullup" above.
But if an RPM gauge originally got the input signal directly from the primary side of the ignition transformer, or you know the gauge needs high voltage to trigger, the above "resistive pullup" will not be enough for RPM signal. Than this inductive pullup is needed.
Take a free ignition (not logiclevel, but IGBT) output (on Roland's ALS BMW 1.6 turbo we used EC36pin10, that is i259 channel 7 as seen on GenBoard/Manual/DigitalOut/Table), configure tach_channel and used an "inductive pullup" to 12V made from a [22 Ohm and 220uH] connected in series.