Conventional Tach on LS2

[Rokcrln]

Originally Posted by TR65

Hey guys,

I bought a cheap Sun Super Tach II to run on my LS2 swap using the tach wire from the ECM (E40). It would not move the needle.

I did some research on the web and several people said that you need to put a "pull-up resistor" in the circuit. The conventional tachs are looking for a 12 volt signal with the speed pulse riding on it. The ECM evidently just sends the speed pulse out on the tach wire at low voltage. So I put a 1000 ohm resistor from the tach power wire to the tach signal wire going to the ECM. So that pulls the tach signal up to 12 volts.

Works like a champ.

TR

TR,
I just did an 05 5.3L swap and I am using the stock style 70 tach and it does not read at all from the ECM's tach wire. So if I install the same 1000 ohm resistor like you did it should all work our fine? Can I just put the resistor right at the back of the gauge under the spade connections? Is their a power and a signal side of the resistor?

Thanks for any further help on this.

Kevin
LFD Inc.