I can't get my my tachs to function.. help! - Lateral-g Forums

**Steve1968LS2** · #1 11-12-2007, 09:52 AM

Spent yesterday trying to wire up my tachs. I have two of them (both Stewart Warner)

The first is the standard elec tach. The other one is their GUS unit (digital shift light with numerical readout). I have a white wire coming off the Speartech harness for the tach signal but I can't get a reading off either unit.

At first I thought it was a bad ground but the GUS unit lights up and seems to be in working order. The normal unit lights up also, but neither shows an RPM reading at all.

I have the GUS set at 2 ppr and the tach set for 4-cylinder.

I was told that the signal from the ECU might be too weak for some aftermarket gauges to read. A suggestion was made to me that I could boost it by tapping a 12v wire to the signal post, but run it though a 4700ohm resistor.

Thoughts?

**XcYZ** · #2 11-12-2007, 10:29 AM

Do you have any other tachs that you could try? I've heard, just like you, that some tachs don't like some of the ECM signals. Did you happen to talk to John at Speartech about it? Curious as to what he has to say about it.

**Steve1968LS2** · #3 11-12-2007, 10:39 AM

Quote:

Originally Posted by XcYZ

Do you have any other tachs that you could try? I've heard, just like you, that some tachs don't like some of the ECM signals. Did you happen to talk to John at Speartech about it? Curious as to what he has to say about it.

I have another Stewart Warner tach in the garage. Could try that.

John suggested the 12v (through a 4700ohm resistor) deal to boost the signal. Will try that tonight.

Stewart Warner was of little help. They just said "it should work" but they suggested tapping into one of the coil packs and setting the ppr to .5 or maybe 1. They didn't know which one of the three coil pack wires to tap into. idea?

I wish I had an extra Autometer gauge laying around to try. Without an osilliscope I can't even see if the wire has a signal.

Payton King · #4 11-12-2007, 11:12 AM

I had a hot wire and a ground wire to the gauge and then the wire from my engine harness to the tach. Set the tach to 4 cylinder just like you said.

Are you sure you are getting key on power to your tach? Sounds to me you have having a power or ground problem since you are not getting any kind of reading.

You don;t need a tach anyways, just shift when it quits pulling...LOL

**Steve1968LS2** · #5 11-12-2007, 11:32 AM

Quote:

Originally Posted by Payton King

I had a hot wire and a ground wire to the gauge and then the wire from my engine harness to the tach. Set the tach to 4 cylinder just like you said.

Are you sure you are getting key on power to your tach? Sounds to me you have having a power or ground problem since you are not getting any kind of reading.

You don;t need a tach anyways, just shift when it quits pulling...LOL

The power and ground MUST be good to my gauges, especially the GUS unit, since it lights up and functions great. It just reads 0 as the RPM. If the ground/power were bad I would think the unit wouldn't light up and display the settings and such.

Here's what I have:

G.U.S.
http://www.sw-performance.com/index....tails&p=114949

Standard Tach
http://www.sw-performance.com/index....tails&p=114115

I guess I could just bounce off the rev-limiter a lot, but the lights are so pretty. lol

Tom.A · #6 11-12-2007, 09:38 PM

Steve,

I sent you a PM. I have one you can try.

Thanks,

murtah · #7 11-13-2007, 12:42 PM

Steve, I am building a car with the same set up. LSX, speartech SW tach and GUS. I would appreciate it if you could post or PM me what you come up with.

Thanks. Jim

Payton King · #8 11-14-2007, 06:28 AM

I am waiting on the video of you beating on that car.

**Steve1968LS2** · #9 11-24-2007, 02:15 PM

The "pull up" circut worked.. although the regular tach seems off and won't go below 1900 RPM... the digital tach works great though.

The normal tach starts to match the digital tach at around 2,600 RPM.. weird.

Anyways, I ran a 12V circut through a 4700 OHM resitor to the tach wire to boost the signal from the ECU. It's nice to have at least one functioning tach

Tom.A · #10 11-24-2007, 02:45 PM

Did the Autometer unit not work?

I'm going to try it tomorrow in place of the SW unit and see if it read differently.

The resistor mod was easy to do so I tried it first.. swapping tachs involves cutting wires (unlike other gauges)

Thanks for bringing that by the office for me... it's going to really help me determine if it's the gauge or something else.