Tachometer recalibration information

[fivetodrive]

I saw this on facebook and thought it was important to post here

‎Jose A Berrios‎ to SyTy.net

I noticed my tach was reading 1000 rpm at idle but my scanner was reading 750 rpm..at 4000 rpms at the dash tach the engine was really at 3000..i read that gm tachs go out of calibration because of a calibration resistor chip drifting ..i opened mine and i found the same calibration chip...to make the story short look at the pictures...i just removed the solder from the pins 4 and 10 on the white chip to remove it from the circuit..this is the bad resistor that drifted out of calibration...and in the same board there is a place marked r 14..there you just install a trio of resistors in series..2 100k and one 47k...total resistance will be 247k ohms...my original measurement of the chip was 306k...i hope this write up can help some of you

 

[fivetodrive]

Re: Tachometer recalibration information

the 4 cylinder board looks totally different. I will try to pull one out of the shed in the next few days...

 

[Static]

Re: Tachometer recalibration information

I know this was also a problem for the G body cars. Specifically the Pontiacs. My mothers grand Prix had to go in to be recalibrated twice. My 2+2 was also way off but I never ended up fixing it. Maybe looking at the G body v8 tach will yield the correct resistor value to calibrate a syty for a v8 readout.

 

[hatrik8]

Re: Tachometer recalibration information

Good thinking to post it here.
Not sure how easy it would be to find a post like this on Facebook if you are looking for the information sometime in the future.

 

[hellcat1]

Re: Tachometer recalibration information

Maybe looking at the G body v8 tach will yield the correct resistor value to calibrate a syty for a v8 readout.

Did you ever find out?

 

[Static]

Negative.

 

[RealFastV6]

Did you ever find out?

Use 100k+50k resistors and a 100k potentiometer to find out exactly, but I suspect it's 200k.

Unless you're talking about an LS1 - in which case it seems most people just change the LS1 ecu output to output for a V6 tach instead.