edis tach setup not working at idle

[Mx73]

i setup my tach as it shows in this http://www.megamanual.com/ms2/EDIS.htm "very bottom of the page" it works but at lower speeds the needle either bounces and is lower or doesn't show anything, but it's accurate when u rev it up.

stock it ran off a single coil distributor. could it just be the diodes aren't sending enough current.

[trakkies]

I think it depends on the electronics inside your tach. I had the same problem with the '80s Smiths unit fitted to my car. It uses a 555 timer which is very sensitive to the shape and amplitude of the pulse it sees. There could also be a variation between samples of the same unit.

I tried this circuit:-



and that worked at low revs, but cut out at high. So I decided to try a different drive circuit for the actual tach, which works ok.

[sammy]

Yes its a bit of a problem for many of us, I never got my old Alfa Romeo tacho working at all.

I tried using Negative from the coils and the diodes, but NBG.
An electronic engineer I know had a look at it. He said the old tacho's curcit design has a particular capacitor in it, when coupled with the diodes I put in it winds up acting like a bypass filter (? Or at least I think that’s what he said).

I also tried pin 2 from the EDIS (i.e. tech out), directly to the tach, but aparently my Tacho expects 24v while the EDIS outs only 9v.

So today I wnet out and scavenged the tacho from the Ford Mondeo that I got the EDIS from.
I ripped the mechanism out, made a small bracket and installed it into my Alfa’s cluster.

I re-used the original Alfa Tacho Face plate so it’s not noticeable.

Its not perfect, but at least I finally have a working tacho … now just need to get over all those other problems I have

Sam