Calibrating a factory tac - The 1947 - Present Chevrolet & GMC Truck Message Board Network

skokie · 02-23-2004, 02:13 AM

Is it possible to calibrate a factory tac? Mine is sitting at -200 when the truck is off.
Thanks

BobbyK · 02-23-2004, 02:47 AM

Where does it sit when the ign is on but eng. not started?
It should be at zero then.

If it still needs "tweeking" there is a small hole in the back of the tach(it may be covered with some type of sticker).

Peel that off.You'll see where you can adjust it there.

skokie · 02-23-2004, 03:47 AM

It sits at -200 when ign is on but not started.

BobbyK · 02-23-2004, 08:24 AM

Try adjusting it as descibed while eng is running.

If you have access to an external tach,test tach or the like,hook that up and use that as well.

You can compare the external tach readings with the indash one and see if they are close to each other.

BobbyK · 02-23-2004, 08:27 AM

Here's a pic I found on this board.The hole at the top of the gauge is where you would adjust it.

02-23-2004, 02:13 AM	#1
skokie Registered User Join Date: Oct 2003 Location: San Jose Ca. Posts: 3,300	Calibrating a factory tac Is it possible to calibrate a factory tac? Mine is sitting at -200 when the truck is off. Thanks

02-23-2004, 02:47 AM	#2
BobbyK Registered User Join Date: May 2000 Location: Petrolia,Ontario,Canada but working in Port Huron,Mi. Posts: 1,769	Where does it sit when the ign is on but eng. not started? It should be at zero then. If it still needs "tweeking" there is a small hole in the back of the tach(it may be covered with some type of sticker). Peel that off.You'll see where you can adjust it there. __________________ 71 blazer,350SBC,approx.375HP,700R4,factory GM TPI.Dual electric fans,33x12.5x15 ATR on stock suspension. Petrolia,Ontario,Canada but working in Port Huron,MI. See ALL my Blazer pic's HERE Last edited by BobbyK; 02-23-2004 at 08:21 AM.

02-23-2004, 08:24 AM	#4
BobbyK Registered User Join Date: May 2000 Location: Petrolia,Ontario,Canada but working in Port Huron,Mi. Posts: 1,769	Try adjusting it as descibed while eng is running. If you have access to an external tach,test tach or the like,hook that up and use that as well. You can compare the external tach readings with the indash one and see if they are close to each other. __________________ 71 blazer,350SBC,approx.375HP,700R4,factory GM TPI.Dual electric fans,33x12.5x15 ATR on stock suspension. Petrolia,Ontario,Canada but working in Port Huron,MI. See ALL my Blazer pic's HERE

02-23-2004, 08:27 AM	#5
BobbyK Registered User Join Date: May 2000 Location: Petrolia,Ontario,Canada but working in Port Huron,Mi. Posts: 1,769	Here's a pic I found on this board.The hole at the top of the gauge is where you would adjust it. __________________ 71 blazer,350SBC,approx.375HP,700R4,factory GM TPI.Dual electric fans,33x12.5x15 ATR on stock suspension. Petrolia,Ontario,Canada but working in Port Huron,MI. See ALL my Blazer pic's HERE

02-23-2004, 03:47 AM	#3
skokie Registered User Join Date: Oct 2003 Location: San Jose Ca. Posts: 3,300	It sits at -200 when ign is on but not started.



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