[Argess]

OK...here's some news. Today I changed spark plugs. All good but 1, and it was a mess (whole 'nother story, but engine is fine). Put new plugs in it and tach works perfectly. Perhaps it is co-incidence as it doesn't make sense. Input signal to tach from coil (-) terminal should be the same no matter what is going on at the High Voltasge side, but possibly it isn't.

So, perhaps new plugs and wires might fix your tach?


ps: if mine starts wandering again, I'll report back here that I was on a false lead with this