Digital rpm/tachometer problem

[Jmac700]

Ok yes most wont like but i love all the aftermarket stuff

I have already an analogue rpm gauge with a shift light, works good, red wire - ignition, black - earth, green - signal to neg of coil, simple stuff

Got a digital one and altho it says the same setup, the results are 5k-6k on tickover and limited to 10k with the slightest revs, maybe its x10 for some reason? It has 2,4,6,8 cyl switch on the back set to 6

Is there other ways to connect the signal wire other then on the coil direct or even to test the gauge

[Grrrmachine]

Can you confirm which model and year of E30 you have?

[Speedtouch]

Also the make/model of tachometer.

[Jmac700]

Yea that would probably help

1990 m20b20 and the gauge is Ket Gauge

[Speedtouch]

Did it come with fitting instructions? Some tachos are very sensitive to the type of input they receive, so you've got to ensure it's seeing the right signal level.

[Jmac700]

Very simple stuff on the wiring diagram, red - ignition, black - earth, green - coil neg, i temp wired under the bonnet same rubbish, has to be a fault with with the rev counter.. Annoying

[Speedtouch]

Not necessarily; it may just need a current limiting resistor or choke on the coil feed, to reduce any spikes (back emf) that the coil may be giving off.

If you were to hook an oscilloscope to the coil, you would see the effect as 'ringing', which throws digital electronics into chaos!

[Jmac700]

Oh no, it should just work, i have a small grasp on resistors, really just for resisting leds from 12v, any ideas on numbers/calculations or can i just cheat and you tell me the answer also think i may be interested in your ecu chips but never adventured into that before

[Speedtouch]

I would suggest trying a 1 kilohm first , then a 10 kilohm. (Kilohm = 1,000 ohm)

The chips are a straightforward plug & play DIY fitment, with no soldering required - see the Zone Wiki guide:

http://www.e30zone.net/e30zonewiki/inde ... ting_Guide