LS6 Cobra swap Speedo and Tach hookup tips
07-28-2011, 04:00 PM
#1
LS6 Cobra swap Speedo and Tach hookup tips I thought that I would post these to perhaps help someone else out there.
LS6 Swap Electronic Speedometer and Tachometer Hookup My Autometer Electronic speedometer would not work after I hooked it up according to the AutometerTech line (and instructions) by tying into the high side of the VSS wire. Here is what the original tech person replied,
As far as the VSS goes, you should be able to utilize it as long as you use one of our electric speedometers (not a mechanical). You *must* tap into the VSS high wire at the speed sensor itself before the computer. This is very important because the speedometer out from the computer is not going to be outputting a signal that our gauges can register. It should be able to pick up off the factory VSS. Just make sure that you get your signal from the sensor before it hits the computer. Once it hits the computer, it will skew the signal.When I hooked it up this way it would operate the speedometer but the shifting function of the transmission was messed up as it would not shift out of second gear. When I disconnected it everything would work fine in the trans. I emailed another tech representative at Autometer and got a different response. Here is his response.
This can be common with some GM PCMs. You can try a couple of different things. First, you may try adding a 1k resistor in-line on the signal wire that is going to the speedometer. This would be placed in the wire going to the speedometer-only. Not in the wire going to the computer or transmission module. Additionally to this "fix", you may have to use a 2nd wire from a known good chassis ground, and tap into the "lo-side" signal of the VSS that is otherwise still going to the computer. If no success, then go to the next step.
Stop using the VSS hi-side wire, and instead go ahead and try the speed-out wire supplied by most computers & trans controllers. This may or may not provide a good signal to the speedometer. If no signal to the speedometer this way, then go to the next step.
Use an ohm meter and with the speedometer electrically disconnected (completely), measure from the SIG terminal of the speedometer to the GND terminal of the speedometer. If the measurement comes out to be 2.9K ohms (2900 ohms) or lower, then send the unit into us for service to have an internal modification done to the circuit board, then upon receiving the unit back, re-connect by simply running a wire from the SIG terminal, and "tapping", or "splicing" onto the VSS hi-side wire (much like you probably had it to begin with). To date this is still a no charge operation.
I was frustrated because I had originally wanted to just hook up the VSS out wire from the Painless harness but was told by the original tech guy that this would not work. When I hooked it up to the signal side of my speedometer it worked great and the speedo calibrated perfectly.
Problem Solved.
Tachometer would not work. The tachometer would not work as it did not have strong enough signal from the tach out line from the Painless Harness, ie ECM. I fixed this by looking online and finding that the signal needed to be boosted up to a higher voltage level to make the tach signal strong enough to operate the tachometer. I hooked up potentiometer to a fused 12 V source and “Teed” it into the tach signal wire that fed the tach. I then adjusted the pot until the tach response was smooth and steady. It worked out to about 8K ohms or so. The tach and speedo were verified using HP Tuners software and are working correctly.
I hope that this saves some people some headaches that are using Autometer type gauges in an LS swap. I put the LS6 into a Cobra Kit car using the Painless harness and GM ECM and it was a good combo with the gauges and the car.
LS6 Swap Electronic Speedometer and Tachometer Hookup My Autometer Electronic speedometer would not work after I hooked it up according to the AutometerTech line (and instructions) by tying into the high side of the VSS wire. Here is what the original tech person replied,
As far as the VSS goes, you should be able to utilize it as long as you use one of our electric speedometers (not a mechanical). You *must* tap into the VSS high wire at the speed sensor itself before the computer. This is very important because the speedometer out from the computer is not going to be outputting a signal that our gauges can register. It should be able to pick up off the factory VSS. Just make sure that you get your signal from the sensor before it hits the computer. Once it hits the computer, it will skew the signal.When I hooked it up this way it would operate the speedometer but the shifting function of the transmission was messed up as it would not shift out of second gear. When I disconnected it everything would work fine in the trans. I emailed another tech representative at Autometer and got a different response. Here is his response.
This can be common with some GM PCMs. You can try a couple of different things. First, you may try adding a 1k resistor in-line on the signal wire that is going to the speedometer. This would be placed in the wire going to the speedometer-only. Not in the wire going to the computer or transmission module. Additionally to this "fix", you may have to use a 2nd wire from a known good chassis ground, and tap into the "lo-side" signal of the VSS that is otherwise still going to the computer. If no success, then go to the next step.
Stop using the VSS hi-side wire, and instead go ahead and try the speed-out wire supplied by most computers & trans controllers. This may or may not provide a good signal to the speedometer. If no signal to the speedometer this way, then go to the next step.
Use an ohm meter and with the speedometer electrically disconnected (completely), measure from the SIG terminal of the speedometer to the GND terminal of the speedometer. If the measurement comes out to be 2.9K ohms (2900 ohms) or lower, then send the unit into us for service to have an internal modification done to the circuit board, then upon receiving the unit back, re-connect by simply running a wire from the SIG terminal, and "tapping", or "splicing" onto the VSS hi-side wire (much like you probably had it to begin with). To date this is still a no charge operation.
I was frustrated because I had originally wanted to just hook up the VSS out wire from the Painless harness but was told by the original tech guy that this would not work. When I hooked it up to the signal side of my speedometer it worked great and the speedo calibrated perfectly.
Problem Solved.
Tachometer would not work. The tachometer would not work as it did not have strong enough signal from the tach out line from the Painless Harness, ie ECM. I fixed this by looking online and finding that the signal needed to be boosted up to a higher voltage level to make the tach signal strong enough to operate the tachometer. I hooked up potentiometer to a fused 12 V source and “Teed” it into the tach signal wire that fed the tach. I then adjusted the pot until the tach response was smooth and steady. It worked out to about 8K ohms or so. The tach and speedo were verified using HP Tuners software and are working correctly.
I hope that this saves some people some headaches that are using Autometer type gauges in an LS swap. I put the LS6 into a Cobra Kit car using the Painless harness and GM ECM and it was a good combo with the gauges and the car.
Last edited by meatheadgn; 07-28-2011 at 04:17 PM. Reason: added highlights to the quotes from Autometer
07-28-2011, 09:30 PM
#3
I had the exact same problem with my Autometer speedo. They 'insisted' that it be tapped directly into the VSS wires, and it totally screwed up the way the trans shifted. I tried about 6 different resistors before it worked, but still wasn't 100% right. Hooking up to the VSS output from the PCM fixed the problem right away. Also when I was calibrating it, driving my marked 2 miles, I realized that the pulses it was counting on the odometer was going to work out to 4000ppm, so when it reached 8000 pulses and I was almost to the end of my 2 miles, I stopped. It works perfectly now. I just cant understand why they say it won't work that way?
