classic instruments - calibrating speedometer??

[demonpixel]

Ok, I have all my gauges working except for my speedometer gauge. The car is a 93 Camaro with an LS1/TH400 swap. My gauges are Classic Instruments gauges.

I have the TH400 reluctor wheel/pigtail conversion; here are the part numbers I'm using:

12085498 - pigtail connector
8655315 - reluctor
24232618 - sensor

I'm having a very difficult time calibrating the speedo.

The instructions say to first identify the type of gauge I'm using by looking at the back of the gauge. Apparently, I'm using a 4 5/8" 16-PULSE speedometer. Here's what the back of it looks like:



Classic Instruments told me I needed to use an SN74 box, and wire it like this:





And that is EXACTLY how I have it wired up. On my LS1 engine harness, I have the green/white wire labeled VSS OUTPUT as my ECM Computer Speed Signal wire in the diagram. So that goes to the INPUT spot on the SN74 box. My grounds are good, the SN74 and the speedo are both getting power. So then after it's all wired up, here is the calibration process (short read): http://www.classicinstruments.com/Us...alibration.pdf

Unfortunately, when I get to 60mph using a speedometer app on my phone, hold the SN74 pushbutton down to get into Real Time calibration mode, and then click the pushbutton again, THE NEEDLE DOESN'T MOVE. I mean it doesn't move AT ALL.

Has anyone ever had experience with a Classic Instruments speedometer and an SN74 box??

I know this post is a little long but I'm not sure where to go from here. I'd call Classic's tech line, but that's the same line that told me to get the SN74 and it's not working. They're also closed on weekend which is when I have time to work on my car.

I'm so close!! One last gauge to go; thanks to anyone willing to help me out at all!

[demonpixel]

Ok, what I did just now was I took the VSS OUTPUT wire out of the Input spot on the SN74, and took the wire out of the Output spot on the SN74, and connected those two wires together. So the VSS OUTPUT wire is now directly wired to the #3 terminal on the back of my speedometer, the signal terminal.

Took it out for a drive at 60mph, and the needle DID NOT move. Brought it home, checked voltage with a multimeter at the power and ground terminals on my speedometer, and I'm getting 12.25 volts, so I know the gauge is getting power.

Anyone have any ideas?

[Mudweizer]

Is the wire good from the speed sensor to the ECM computer?

[demonpixel]

Is the wire good from the speed sensor to the ECM computer?

That's what I was thinking too. Maybe the signal is not getting there, or the signal is not getting from the PCM to the gauge.

How do I test to see if the PCM's vehicle speed output wire is putting out a signal without an expensive oscilliscope?

[Mudweizer]

This one is 207$, cheapest I know of: http://www.picotech.com/handheld-oscilloscope.html it uses a laptop.

Have you checked continuity of the wire at least?

[demonpixel]

A friend of mine had a Cyberdyne digital gauge sitting in his garage. I wired the + and -, and connected the gauge's signal wire to the vehicle output wire from the pcm. Then I went for a drive.

The gauge the entire time read 0mph. So I don't think I'm getting a signal from the PCM at all. I will try to retrace the wires from the VSS on the transmission; I think that's a good place to start.

[newvintageusa]

Try picking up the signal directly off of the VSS
Mark

[demonpixel]

Try picking up the signal directly off of the VSS
Mark

That's a good idea, I'm going to try that as soon as I get home from work.

Now there are two light gray wires coming off of my vss at the trans. How do I know which one to splice into? I know one is a high signal and one is a low signal.

[69keith]

is that the one you have to set it and drive exactly a mile and the hold the button??? if your cruise works you are gett vss speed signal

[newvintageusa]

One is usually a ground, one a signal.
use a multimeter, and check for an on-off (open-closed) signal as you roll the car

The VSS sender is nothing but an on-off switch that "pulses" on and off mant time per mile

Most ECUs just pass the signal through, so no reason to go through the computer unless you are in a state that plugs into your OBD/CAN port during an emission test.

Hope this helps
Mark

That's a good idea, I'm going to try that as soon as I get home from work.

Now there are two light gray wires coming off of my vss at the trans. How do I know which one to splice into? I know one is a high signal and one is a low signal.

[demonpixel]

Ok gotcha. Now if I don't get an on-off signal, I assume that wire would be the ground wire, in which case it will just give me a constant reading on the multimeter. Is that correct?

[demonpixel]

is that the one you have to set it and drive exactly a mile and the hold the button??? if your cruise works you are gett vss speed signal

Yes it is. I don't have cruise control. BUT the green LED light is blinking when I'm driving, and that's supposed to tell you that you are in fact getting a signal from the PCM.

I have been emailing back and forth with Classic Instrument's tech line all morning, so I have some stuff to try out.

I will test as soon as I get home and let you guys know how it goes!

[demonpixel]

Ok, I spoke with Classic Instrument's tech line - it was a misprint in the instruction manual.

Where it says:

Step 5: Follow the procedure below to fine tune the speedometer calibration (if necessary).

1) Enter the calibration mode selection as detailed in step 3.

2) Push and hold the pushbutton with red LED “1” lit until LED “1” starts blinking. (approximately 5 seconds)

3) Drive a known speed (use GPS or pace another car).

(and here is the misprint):
4) The first time the pushbutton is pressed, the speed shown on the speedometer will increase. The second time the pushbutton is pressed, the speed shown on the speedometer will decrease.

5) The pushbutton will alternate increasing or decreasing the speed shown on the speedometer each time it is pressed. Press and hold the pushbutton to fine tune the speed shown on the speedometer.

Step 4 above SHOULD say this:

4) Then press and hold the pushbutton to make the speedometer needle move. The first time the pushbutton is pressed and held, the speed shown on the speedometer will increase. The second time the pushbutton is pressed and held, the speed shown on the speedometer will decrease.

I was just clicking the pushbutton to try and make the needle go up or down. All I had to do was press AND HOLD the button until the needle moved.

The gauge works perfectly now.

Classic Instrument's tech line had told me that if the green LED is blinking, that means I am getting a GOOD signal from the PCM's vehicle speed output wire. They also said that for my particular gauge, it was NOT designed to splice directly to a VSS wire.

Now all my gauges work; MAN I am happy. Thanks for all your help guys.