Tach reads 50%

Happened to me on my current car a couple years back. It needed to be sent out to be fixed. North Hollywood Speedometer, if I recall correctly.

 

By chance did your mileage go up by 100% ?

 

Mine reads 200% or more after the car is warmed up. I haven't gotten around to trouble shooting it yet but from several threads about errant tachs, it can be a distributor/ignition system issue and have nothing to do with the tach. Just putting that on your list of things to look into. Would really suck to spend big bucks on a tach refurb and have it come home doing the same as before.

Best!

Hannibal

 

First thing to do is clean the connections for the tach on the left rear rail by the two coils. I think there is a thread with pics. Next is swapping the digiplex connections to see if it changes the readings. +1 for N. Hollywood Speedo.

 

Does anyone know if this looks right? I just got a 1986 fully restored 328GTS. The car looks great. When I purchased the car the tach was sluggish. It was sent out to be repaired in Palo Alto. When I got it back it still seems slow. From the sound of the engine it sounds like the revs should be much higher but it only goes to about 2500 rpms. Any advice?https://vimeo.com/116579948
What do you guys think? Am I crazy?


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The tach on my '89 328 was acting similar to this after I'd first bought the car, but with more frequent driving than was done by the previous owner, the problem showed up less and less.

Interestingly, since spark plug wires and extenders were replaced as part of major servicing, the behavior hasn't shown up at all (fingers tightly crossed...). That could just be a coincidence, but I wonder if there's some way that the ignition system electrics would affect the tach. Doesn't seem like it, but maybe some sort of electromagnetic interference could come into play.

 

See the other thread on this topic, very close to this one.

Cheers,
Rich