Factory Instrument Panels

[Ludis Langens]

"Scott Feaver" <sfeaver at cgocable.net> wrote:
> The reason I am asking is I need to adapt a tachometer module from a 90
> Turbo Sunbird to a 91 Sunbird.  The difference is the 90 is a four cylinder
> car, and the 91 is a 3.1V6.  The tach is reading about 50% higher in the V6
> (which makes sense because for every 2 pulses it expects to see, it receives
> three).

As other's have mentioned, GM likes to use the NatSemi chip.  GM's
circuit is almost the same as the schematic in NatSemi's data sheet.  An
RC combination calibrates the tach.  I doubt you can find a temperature
stable capacitor of the correct value.  So you should change the
resistor.  On the tach circuit board you'll find a thin (thick?) film
resistor pack (in a DIP package).  The resistor element on the top layer
is the calibration element.  You'll notice it is laser trimmed/cut. 
You'll need to bypass this resistor with your own.

What's the redline on the 2.0turbo tach?  The 3.1 might need a different
limit - probably 6000 rpm.  Of course this is just an instrumentation
issue.  The tach redline needn't agree with the ECM redline.

"David A. Cooley" <n5xmt at bellsouth.net> wrote:
> Usually there is a resistor to be changed in a tach for the number of
> cyls... not sure if the dash's had a switch or jumper or socketed resistor,
> but I can't see them using 2 different tachs for the same year, different
> engine...

Wanna bet?  A parts book shows eight different tachs used in one model
of car over a five year range.  (L4 vs V6, US vs Canada, non-backlit vs
backlit, w/ oil gauge vs w/ volt gauge vs w/ no gauge)

-- 
Ludis Langens                               ludis (at) cruzers (dot) com
Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/