Speed Sensor Help

bigwied · Jul 12, 2014

Im installing a autometer hall effect speed sensor for an electric speedo in my 89gt with a tko 600.Car originally had a vss(for cruise control).Can I wire the autometer sender into factory wires at the transmission that run to the computer?Will the computer recognize the signal?Will I have stall issues? I plan on tapping into wires in kick panel for speedo signal.

jrichker · Jul 13, 2014

There have been posts asking the same question and a search may help find the answer.

You will need to use both VSS wires to supply signal to the speedo. Be careful because one of the speedo connections might be a ground which will prevent the cruise control from working and set code 27 or 29. It won't hurt the computer, but it will set a code. If you get either code, you may also have idle/stall problems when slowing down to stop.

smkshw · Jul 13, 2014

jrichker said:
There have been posts asking the same question and a search may help find the answer.

You will need to use both VSS wires to supply signal to the speedo. Be careful because one of the speedo connections might be a ground which will prevent the cruise control from working and set code 27 or 29. It won't hurt the computer, but it will set a code. If you get either code, you may also have idle/stall problems when slowing down to stop.

im having this issue also,plugged the factory plug to the sensor that came with the tko,then tapped the speedo into the same sensor,speedo works,but cruise control dosnt work and the car does want to stall here and there?,if anyone knows the fix to this that would be great.

jrichker · Jul 14, 2014

smkshw said:
im having this issue also,plugged the factory plug to the sensor that came with the tko,then tapped the speedo into the same sensor,speedo works,but cruise control dosnt work and the car does want to stall here and there?,if anyone knows the fix to this that would be great.

Can you post the diagram that came with the speedo? I suspect that one of the wires for the speedo pickup may be a ground. There is no ground in the VSS circuit, it floats. If it is grounded, the computer and the VSS don't work.

The answer may be as simple as grounding one of the speedo input leads and connecting the other to either one of the VSS wires.

Short version of how the VSS works:
The VSS sensor is in effect a miniature AC generator, and the output frequency is a function of how fast you are going. When you press the set speed button, the VSS computer records the frequency coming from the VSS sensor at that time and puts it in memory. The VSS computer takes the signal coming from the VSS sensor and compares the frequency to the one stored in its memory. If it is different, it changes the voltage that is sent to the vacuum regulator for the vacuum servo that works the throttle.

smkshw · Jul 14, 2014

jrichker said:
Can you post the diagram that came with the speedo? I suspect that one of the wires for the speedo pickup may be a ground. There is no ground in the VSS circuit, it floats. If it is grounded, the computer and the VSS don't work.

The answer may be as simple as grounding one of the speedo input leads and connecting the other to either one of the VSS wires.

Short version of how the VSS works:
The VSS sensor is in effect a miniature AC generator, and the output frequency is a function of how fast you are going. When you press the set speed button, the VSS computer records the frequency coming from the VSS sensor at that time and puts it in memory. The VSS computer takes the signal coming from the VSS sensor and compares the frequency to the one stored in its memory. If it is different, it changes the voltage that is sent to the vacuum regulator for the vacuum servo that works the throttle.

ill see if i can find it,but the tko came with the sensor already installed,minus the mechanical speedo,but it had the same plug as the oem one,plugged that in and basically taped one speedo wire to one side of the plug,cant remember what color of hand,but the one they specified,speedo works perfectly but ya cruise dosnt now....i remember before when i let off the clutch and took it out of gear it used to slowly drop the reves down back to idle,but dosnt do it anymore,maybe wrong sensor?,i dont know,still working on it...

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