Mark J Bradakis wrote:
> [BOUNCE triumphs@Autox.Team.Net: Non-member submission from [Mike Ginter
> Date: Wed, 26 Mar 1997 08:32:52 -0700
> From: Mike Ginter SA <firstname.lastname@example.org>
> Subject: Re: Elect. tach. vs. mech.
> While we're on the subject, my electronic tach reads 10K over at idle, (1800
> to 2000 rpm) and approximately 10K under at seemingly peak torque (4000 rpm
> I've never run the thing over what the tach says is 4500 rpm, because at that
> point, the engine doesn't seem to have anything left.
> Occasionally upon engine startup, the tach reads normal at idle (800 rpm)
>until the throttle is punched up to approx. 1500 rpm. At this point it
> 10K overage and stays there for the duration of the drive.
> I had only seen it behave normally at idle once before I put in a new
> distributor cap and rotor. Now it is normal almost every time I first start
> the car, until I give it some gas, and then it returns to the aforementioned
> Can someone explain to me the theory of electronic tach operation and all of
> the components involved so I may begin to troubleshoot this problem without
> having to buy all new parts in a process of elimination?
> Any help would be appreciated.
> 79 Spit
Mike: Send it out to be recailibrated. Most electronic tachs have a
potentiometer inside for that very purpose. You could do it your self,
but you'd have to rig up a second tach that is know to be accuate. Then,
you'd have to rig your tach in such a manner that you could get at the
innards to adjust the pot., while comparing it to the know accuate one
at a variety of rpm ranges.