Auto Meter tach on an LS3 inop

[Mastertech5]

My FFR Auto Meter tachometer isn't working. I connected the signal terminal to the tach output wire as specified in the directions. The factory LS3 computer harness that came with the crate engine has a bulkhead connector with certain outputs for use for gauges and a few other things. It says that it outputs a 2 pulse per revolution square wave signal (4 cylinder). I set the dip switches in the tach for that. I bought a LS install kit from Auto Meter that comes with an installation manual that has some diagnostic tips. It says to check for DC voltage on the signal wire with the engine running. It should read 0.5 to 3 volts but there is no absolute spec. The voltage should go up significantly when revved up. I got 16 on the meter. No point anything, just 16. I have an auto ranging Fluke meter. The voltage does not change when revved. The AM LS install kit came with a resistor to step up the signal strength. For anyone with an LS using the factory computer and the Auto Meter gauges, how did you wire your tach. I know of 2 off hand, edwardb and JimLev that have the LS set up but don't know about their gauges. Any advise is welcome. I'm calling Auto Meter Tech support on Monday. Hopefully they can help. Why would my meter read 16V I wonder.
Funny thing. I started the engine in my garage 3 times for less than a minute each with the door closed. About 6 hours later my CO alarm at the bottom of my stairs near the inside garage door went off. I had never opened the outside door to air things out so I opened my front door, basement door and garage door for about 15 minutes. With a decent breeze outside it aired out. Those CO alarms really work. Plugged it back in and it stayed off. I'll open the door next time. I got a lot of wife grief with that dumb move.

[edwardb]

For my truck build with an LS3 crate motor and the Chevrolet Performance electronics pack, my tach didn't work at first either. This is the post from my build thread where I described how it was fixed:

"Tach not working: Both the Chevrolet Performance and Autometer instructions describe that the tach output wire from the ECU may be too weak for analog gauges. The easiest first solution is to install a “pull-up resistor” between the tach wire and +12 volts at the gauge. The recommended value is a 10k ohm 1/2 watt. Didn’t have any on hand, but next day from Amazon had some. Pulled the dash and clipped the resistor in temporarily. Success! A little more work and the resistor was soldered between the two leads on the gauge harness. Confirmed the proper 4-cylinder setting in the gauge (interestingly that’s the setting used for the LS) and confirmed the indicated RPM on the gauge matched with the data stream from the ODB2 port. Fixed."

https://thefactoryfiveforum.com/show...l=1#post473831

Hope there's something there that works for you.

[JimLev]

I used a 10K resistor like Edward mentioned, my tach works.

[Its Bruce]

I also had success with resistor (11K ohm bc it's what I had on hand) and tach (Speedhut).

[Mastertech5]

I'll try the resistor supplied from Auto Meter. Thanks all! Watch this page.

Update. I made two short jumpers with the resistor in between the power feed and the tach signal wire to test before permanent install. I will start it on Monday to see if that fixes it.

[Mastertech5]

YES, it works. Thanks everyone!