After installing a newer engine into an older european car (engine swap), I am trying to find a solution for driving the stock tachometer.
The old engine has a distributor/coil ignition where the tachometer is driven from the coil.
The new engine has the newer type ignition with no coil and a tach signal wire coming from the computer.
The signal from the engine computer will not drive this tach.
I do not have an oscilloscope but I may have enough information from simple DMM measurements. With the old coil ignition, the DMM set for AC Voltage shows around 28 volts and it wanders up and down a couple of volts. With the newer engine the meter shows about 18 volts on just the bare signal wire from the computer, and that wanders a bit as well.
With just those two measurements I am thinking the tachometer just needs a higher signal voltage to make it run. It's automotive so I have about 14.5 volts to play with from the alternator. I'm thinking maybe if I doubled the signal voltage supplied to the tach, that might make it go? I've been poking around for a while looking for solutions and I hit upon charge pump ICs that can take 15V and put out 30V using capacitors. Would that work, or does anybody have more insight on why the tach won't move?