Factory Instrument Panels

[Marc Piccioni]

Usually tach's use a RC circuit to integrate the ignition pulses into an 
average DC voltage which drive the actual meter, I suggest tracing out the 
tach's internal circuitry and finding the RC network. Repalcing the fixed 
resistor with a pot and calibrate the tach using a reference tach will get 
you going.

----------
From: 	Scott Feaver[SMTP:sfeaver at cgocable.net]
Sent: 	January 12, 1999 6:38 PM
To: 	diy_efi at efi332.eng.ohio-state.edu
Subject: 	Factory Instrument Panels

Has anyone ever used a GM gage package in anything that they have adapted 
to
EFI?

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).

If there is no simple solution, does anyone have a circuit that will delete
every third pulse from the spark module?  I don't know what voltage the
signal is, but it is a 3.1V6 with the distributorless 3-coil module.  Since
there fairly common, i'm hoping someone knows ;)

Thanks,
Scott




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