I have a stock Alfa 75 Potenziata and am trying to calibrate my tachometer. I think it is reading low and would like some info from other 75 Potenziata owners. If anyone could tell me what their tachometer is reading in 5th gear when their speedometer is at 100kmh? Possibly what it is also reading at 80kmh ? Mine reads about 1900-2000 rpm at 100kmh, which I suspect might be on the low side?
Thanks for any info
I can't help you with what you're after as such, but how about putting a digital multimeter on the tacho signal line that comes from the coil?
RPM should equal signal in Hz (pulses per second) divided by 3 (because there will be 3 pulses per revolution) and multiplied by 60 (because seconds).
Or pulse frequency multiplied by 20. ;D
Thanks Duk,
I do have a Fluke multi meter that registers RPM when connected to the No.1 spark plug lead but that didn't give me any consistent readings. So was hoping a member on this forum might be able to give me some data on what their vehicle's readings might be.
Does this run an early Motronic? I thought you could read RPM off most such ECUs with the diagnostic connector.
Or - does it run a 7-pin ignition amplifier? Easy to tap the coil control feed off that, as Duk says.
If you don't get a decent answer, then perhaps look at simply getting signal from the ignition coil's negative terminal rather than a plug lead adapter contraption.
After trying to use a multimeter and having no luck, I downloaded a tachometer app on my phone to do this job on my 75 TS. It uses the microphone and picks up the engine sound.
It was bang on where it should be, for a while. The tacho has fallen out of adjustment again so I need to do it again.