Speedhut speedo issue

[rcarson25]

I have 1978 Firebird with a GM LS3 Connect and Cruise setup. All of my gauges seem to be working well with the exception of the electric (non gps) Speedhut Speedometer. I have a VSS sensor feeding the ECU and I have the Vehicle speed out wire from the bulkhead connector setup as the speedo signal wire and the ground is the vss ground. When I start the car the speedo jumps to 20mph and the odometer is moving. I have hooked up HP tuners and I can see the ECU does not show any MPH from the ECU. I have things setup the way Speedhut says with the step down resistor between a 12v switched source and the signal wire. Am I doing something wrong here? I don't believe calibrating will fix the issue because it is obviously getting signal at rest. Thanks in advance.

[CapSS92]

I checked both manuals and there is no resistor wired in the circuit. Only the tach uses that setup. You should have a straight connection from the bulkhead to the speed input wire. Which ground are you referring to? Some of the Speedhut speedos have two wires, one signal and one ground. In those cases the wires can connect direct to the sender but if you're using the ECM you would only use the signal wire. I attached some links from Speedhut and the GM instructions. HTH.

Alex

Vehicle Speed (BROWN) – This is a non scaled output for use with
auto-scaling speedometers and will not function unless a vehicle
speed sensor (VSS) is connected to the ECM through the VSS wire
in the harness.

https://www.speedhut.com/instructions/speedometer_338_4_412.pdf

https://www.speedhut.com/instructions/speedhut_speedometer_instructions1.pdf

[rcarson25]

I have two yellow wires, 1 yellow red(signal) 1Yellow Black (ground)

So currently I am setup as the optional setup provided in the first link you have listed. In this scenario the gauge is getting the signal from the ecu/brown wire from bulkhead. When using the ecu the instructions to use a 12v switched power and a 4.7k to 10k .25 ohm resistor to tie into the signal wire. The yellow black should be grounded (currently that is grounded.

Because the brown wire in the bulkhead is not scaled does that mean I can run the bulkhead brown wire directly to the yellow red(signal) wire and don’t need the resistor and 12v accessory in place?

[CapSS92]

It must be something new as far as hooking up the speedo. I've never seen it done like that. I would say run it without the resistor and 12v connection and see what it does. I doubt you would fry anything.

Alex

[130fe]

Are you able to hook up an obd2 scanner and see what your VSS signal is coming from your PCMwhile driving? Have you changed any of your VSS parimeters in the tune (gear, tire size)? What trans are you running?

[rcarson25]

Are you able to hook up an obd2 scanner and see what your VSS signal is coming from your PCMwhile driving? Have you changed any of your VSS parimeters in the tune (gear, tire size)? What trans are you running?

I have not driven the car with the scanner on it yet and I have not changed any parameters yet either. However, I have had the scanner hooked up with the engine on and the speedo on the scanner is at 0 while the engine is at idle and the Speedhut speedo is sitting at 20mph. So, I know the ecu is not sending a signal to indicated the car is in motion.

- - - Updated - - -


Are you able to hook up an obd2 scanner and see what your VSS signal is coming from your PCMwhile driving? Have you changed any of your VSS parimeters in the tune (gear, tire size)? What trans are you running?

I have not driven the car with the scanner on it yet and I have not changed any parameters yet either. However, I have had the scanner hooked up with the engine on and the speedo on the scanner is at 0 while the engine is at idle and the Speedhut speedo is sitting at 20mph. So, I know the ecu is not sending a signal to indicated the car is in motion.

[csouth]

Personally I would wait until you calibrate the Speedo before saying there is an issue, but I don't always do things right...lol Seriously, my Speedhut gauges never had an issue. Put them into calibration mode, drove up the street, verifed the correct speed by my GPS app on the phone, called it good. Hopefully you'll get it figured out.

[rcarson25]

Personally I would wait until you calibrate the Speedo before saying there is an issue, but I don't always do things right...lol Seriously, my Speedhut gauges never had an issue. Put them into calibration mode, drove up the street, verifed the correct speed by my GPS app on the phone, called it good. Hopefully you'll get it figured out.


Are you running a similar setup to me? Meaning, does your speedo signal coming from the ECU? If so, did you set it up the way I did with the resistor or did you use a different method?

i talked to speedhut yesterday and the tech there seemed to think it was odd to be showing 20mph as well. They said it was okay to feed tack and speedo off of the same 12v source but I am wondering if that may be causing the issue.

I know a lot of guess work and trial and error can be done. Really hoping to find an answer from someone with a similar setup so I don’t spend a day trying to track this down.

[csouth]

Are you running a similar setup to me? Meaning, does your speedo signal coming from the ECU? If so, did you set it up the way I did with the resistor or did you use a different method?

i talked to speedhut yesterday and the tech there seemed to think it was odd to be showing 20mph as well. They said it was okay to feed tack and speedo off of the same 12v source but I am wondering if that may be causing the issue.

I know a lot of guess work and trial and error can be done. Really hoping to find an answer from someone with a similar setup so I don’t spend a day trying to track this down.


My speedo signal is actually coming from a module that bowler sells for the T56 to run VSS and Reverse Lockout but it does what your resistor does with the voltage conversion.

[dhutton]

Remove the pull-up resistor and give it a try as suggested above. I have never seen a pull-up resistor used there.

Don

[icemanrd19]

Pull up resister is only for the tach signal. Gmpp bulkhead has a speed out that you use for the speedo

[rcarson25]

Thanks for helping me walk through this. I made some changes yesterday, took out the resistor for the speedo and it seems to be working right now.