Steve1969LS1

iTrader: (1)

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.

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


Thoughts or ideas?

Steve1969LS1

iTrader: (1)

I'm the only one ever to have had this problem? lol

Lucky me..

topless 69

iTrader: (1)

I had the same problem with my Autometer tach , sent it back to Autometer
to have it set to work on lower voltage. Still doesn't work, tried all settings etc.
Speartech told me it could be a setting in the ECM. Haven't had time to take it to
a tuner yet.

angelR

iTrader: (7)

Double check that the tach signal is making it to the end of that tach output wire.... it could have been pulled out or otherwise broken somewhere along it's length. My tach wire did this, after buying a second tach thinking my factory one was fubar'ed I ran a new wire to the correct pin and bam.

Rodder

iTrader: (2)

Steve: you may need a lower resistance resistor to bring the voltage up to where the SW tachs can read it. It'll depend on the internal resistance of the tach. Check out posts #22 and #24 in this thread:

https://ls1tech.com/forums/showthrea...t=96783&page=2

Steve1969LS1

iTrader: (1)

1. How do you check for Tach signal? Don't you need an osiliscope? Also, how do you find out which pin on the ECU is for tach signal?

Steve1969LS1

iTrader: (1)

The question is what size I guess... Speartech said "4700ohm" but that thread mentions 13000ohm and even 380ohm.

I guess I will buy a few varients.

deuce_454

id think that the square wave signal from the ecm was the problem... the tach is configured to accept a sinus wave... fiddling arround with resistors seems like a way to "fool" the tach to accept the signal as an alias...

there must be an interface box that solves it the right way

OldSchoolFormula

Not a ton of help, but I'm running the same tach in 5" right off the ECU. I had problems with the speedo bouncing, an in-line resistor solved that in case you get that issue.

angelR

iTrader: (7)

Take a peak at your year's pcm pinouts.... they are posted on this site.

Steve1969LS1

iTrader: (1)

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

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

Rodder

iTrader: (2)

I wonder if a filter would help? (or if you can even use one with the pull-up...) http://www.camaros.net/techref/electrical/tachfilter/

a10beav

I had a problem as well, but it was because I had F-body coil packs and a GTO ECM. The tach never worked until an in-line signal calibrator was installed. I took it to a shop to get it figured out, so I don't know the part number or manufacturer they used.

Steve1969LS1

iTrader: (1)

Also, I calibrated my speedo today.. it works great when the car is moving but at idle (when the car is stopped) it swings around wildly...

Any ideas?

ls1_chevelle

iTrader: (9)

Everyone knows how many times I have posted about no tach signal... I put a 480ohm resistor inline with a 12volt wire. Ran that to my signal wire on the tach and it works perfect!!!!

Steve1969LS1

iTrader: (1)

See.. I ran mine through a 4700 ohm resistor.. would a 480 work better or is the 4700 enough?

Maybe the standard tach isn't getting good enough signal yet..

I will post up what SW has to say on the matter.

ls1_chevelle

iTrader: (9)

not totally sure Steve. All I know is I have struggled for so long, Even went off the coil packs but thats a 1 cyl output.

I have read of about 4-6 guys on here with the 480ohm and it has fixed their problems. From Autometers, to stewart warners, to pep boys, etc.. A wide range so It would be a safe bet to run 480.

-Matt

Steve1969LS1

iTrader: (1)

Just trying to decided if I should try the 480 ohm on the regular tach and leave the 4700 on the digital tach with the shift light (man that thing is fun!)

The digital tach can be set as low as .5 PPr so it would work on even a 1 cylinder.. LSx engines are set up as 4cylinder (2 PPr).

Oh, the stance on your Chevelle is perfect.. where are you located?

OldSchoolFormula

Your solution for the speedo is a resistor. I had the same issue and finally figured it out after a YEAR. SW was no help, dakota digital no help, no answers here. I don't remember what OHM rating mine was, I bought a big box and the first one I tried worked.

ls1_chevelle

iTrader: (9)

So your running both in your car at the same time? Any particular reason?

Thanks for the comment, it took some time but I got it to somewhere I like. I'm located in Red Deer, Alberta. Canada eh.