Dear all:
I've been reading the recent messages on speedo error and have a question
of my own: what about tach error? My '67 4/4 has an electronic tach, mfg.
by Smiths (natch), that is WAAAYYYYY off. As much as we all know how free
revving and eager the ford mill is, I am virtually certain that in fourth
gear at an indicated 55 mph, my engine is NOT revving at 5500 rpm... more
like 3500. Knowledgeable car-guy passengers have often remarked on this.
The PO pointed out to me that he had taken pains to count 'the number of
loops' in the tach and was quite confident of its accuracy. Well, sir,
uh... So, any thoughts? I am frozen on this, basically because its an
electrical thingiemabob and I don't know one heck of a lot about auto
electrical thingiemabobs. I'm assuming the tach is trying to read rpm off
the coil, but how is it making this error?? It appears to be a pretty
consistent error on a % basis. That is, it isn't always about 2000 rpm off
(the indicated idle is about 1600 rpm and I'm sure its really at about
8-900, so its as if its making a 2X error at all times). That strikes me
as an electrical thing, not a mechanical (rebound spring) thing. Is the
tack interpreting the signals as from a V8 and multiplying by two???
Comments/suggestions?
cheers,
Will Zehring
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