Can't get my tachs to work.. argh!

[Steve1968LS2]

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?

[OHCbird]

Did you see if a tach signal conditioner (ala Autometer) would square things up for ya?

On second thought- do you have anything that can confirm you actually have a signal on the white wire? Most DVOMs with an inductive or data pickup will read it.

[Chris442]

Steve, have you tried playing with the signal output options in the PCM? You can change the type of signal output and the number of pulses (I think).

I've been having the same issues with a repop tach in my '68. It's hooked up in the same manner. I haven't had much chance to play around with it yet, though. Same issue with my speedo with VDO guts.

Right now, I just have to keep telling myself that know how fast the car and engine are going is totally overrated. The same thing goes for carpet, inside door handles, not being able to see the ground through the floor and door panels. :drive:

[matty b]

is it the stock ls2 computer? if so OHCbird is correct in telling you to get the tach adapter, I ran into this a long time ago and the nice guys at classic instruments
told me that the tach signal was pretty weak coming out of the pcm and that the tach adapter was what I needed... they were definitley correct so Id try that out

[Steve1968LS2]

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 :woot:

I wonder what the difference is between my $2 pull up circut and the more expensive tach adapter?????

[OHCbird]

...an imbedded impedence-matching transformer, and a 'damping' circuit. On my 4 Runner swap (supercharged 3.4 from a 2K into my 93), I had to use one to run the TFC 'piggyback' computer & the tach. I'm with you Steve- I remember when the 02 sims and IAT 'trickers came out- nothing but a factory connector and a resistor.

The 12V boost is probably causing the one tach to read funny- it won't have the true pulse 'off' signal that the tach needs to effective count your pulses. All the 4700 ohm'r does is make the signal appear to be bigger, but at decreased resolution. Do I make any sense?