jw33

iTrader: (8)

So my Autometer tach is not working and I have the tach signal coming in from my bulkhead connector. I am using one of the new GM swap harness kits and it says,

"A tachometer signal is included in the bulkhead connector. This is a 2 pulse/rev output which may correspond to a 4-cylinder setup in some tachometers. Note the signal is a low voltage square wave and some older style of tachometers may need a pull-up resistor in order to read the signal."

I'm about 99.9% sure I have the tach wired up correctly, but I get nothing no matter if it's in 4, 6, 8 cylinder mode. This is a brand new tach also. It says on Autometer's website that the tach uses a 12v square wave and I have no idea what GM's "low voltage square wave" is.

If I need to use a pull-up resistor I am assuming I will attach one side of the resistor to my switched/ignition 12v source and the other side of the resistor will got to my tach signal wire before it goes into the tach? How do I determine the resistor size? I have a scope I can see the signal with if I need to.

MEFISTUFF

We use a 680 ohm, 1/2 watt resistor for the pull up. you are correct on how to connect it up. steve

68shortstep

iTrader: (1)

i used a 1000ohm, 1/2 watt resister..... the 680ohm one was a little bouncy below 1000RPM the 1000ohm one made it better...

jw33

iTrader: (8)

ha, I just got done messing around with it using a 680 ohm resistor and I was going to ask if there was a way to smooth the needle out at below 1500 rpms. Thanks....

Project GatTagO

iTrader: (7)

I just installed a 1K ohm resistor and the tach is still a little bouncy below 1500 rpm. Any other suggestions?



Andrew

babydeuce

iTrader: (24)

Watching this thread, My autometer bounces bad under 1K, above that it is fine.

Jack

Rodder

iTrader: (2)

my autometer tach works fine with no resistor ('99 Fbdoy PCM).

You might need a filter.

Project GatTagO

iTrader: (7)

OK. Pretend I know nothing (when talking about electronics, that's pretty much the case). Elaborate. Filter? What am I filtering? Where is it filtering? Why am I filtering it?

Andrew

Rodder

iTrader: (2)

http://www.camaros.net/techref/electrical/tachfilter/

Project GatTagO

iTrader: (7)

Results here:

https://ls1tech.com/forums/showthrea...879985&page=12

Andrew