MParks

I'm having problems with getting my speedo to work with my Cable X. I wired it all up exactly like the instructions/diagram told me to. I tested it and it works great. Ran at 16mph like it should (I have the 30 slot disc Cable X).

When I drive the car the speedo does not work at all. I have set my dip switches. The installation instructions say its a signal problem but its all wired properly? I tried switching the wires thinking that might be the cause but turns out it makes no difference.

Any help on this would be great

MParks

Possibly the VSS sensor itself? Thats the only thing I can think of

jmd

iTrader: (4)

To what do you have the red wire connected?

http://www.atrol.com/speedometer/cab...tion_chart.htm

Tuned Performance

iTrader: (92)

you didn't mention your dip setting is this a T56 4k vss ?

MParks

I have the red wire connected to the 12v IGN switch

From what I have read its 4000ppm. Its a 95 T56 out of a trans am. Do you go by the formula they give you? (teeth on transmission exciter gear) X (rear axle ratio) X (revolutions per mile of your tires) which is the way I did it originally 17x3.23x749 revs per mile

or is it just 4000ppm x .267 for the 30 slot cable x?

I might be doing it wrong in that sense

jmd

iTrader: (4)

Some documentation on VSS can be confusing. JTRs included.

4004ppm is a calculated number based on speedometer gear teeth compensating for rear axle ratio and a 4 pulse per driven gear revolution VSS going 1001rpm@60mph.

Quite different than the multiple pulses per revolution of the reluctor / hall switch setup in the T56. The vast majority of the F-body T56s have a 17 tooth reluctor wheel.

Abbot doc says: (teeth on transmission exciter gear) X (rear axle ratio) X (revolutions per mile of your tires) which for you may be:
17 x 3.23 x 749

Much different than the third gen VSSs!

MParks

Thanks JMD thats gives me a better understanding. Looks like I have calibrated it properly. The way I have it hooked up from the VSS is one wire going to the signal wire on the cable x and the other to a ground wire from the automatic. Does it matter which wire from the VSS goes to ground? Im honestly lost and cant figure this thing out at all

jmd

iTrader: (4)

There's your problem. The two-wire VSS needs one wire to 12v and one to the PCM or in this case, the Cable X. The VSS needs powered.

MParks

That makes sense! So there's no ground with the VSS, its just the signal wire to the Cable X and the other to a 12v source. I'm assuming the 12 volt source will be switched?

jmd

iTrader: (4)

Switched is correct. 5v or 12v will work. There are other nearly identical hall effect sensors which have a third wire for ground.

MParks

Ok so I tried hooking it up to a switched power source (12v IGN), and the other wire to the cable X. Still nothing. Even tried switching the wires around. I have power at the Cable X but when I drive the car the speedo still doesn't work

Heres how I have it wired up

Black wire from cable X grounded to the body
Red wire to 12v IGN
White Signal to VSS

From the VSS. I have an aftermarket pigtail so the colors are Purple and Green
Purple to white signal wire on Cable X
Green to 12v IGN

jmd

iTrader: (4)

Not doubting your wiring skills but since we theoretically are correct, now verify with your volt meter you actually have 12v switched at that red wire@CableX and at the green wire@VSS.

And continuity from purple/white to signal@CableX.

I'm not Captain Electrical so I'm not sure what volts or ohms purple should show when green has 12v. But if you have a tach/dwell meter, I believe that should function as a monitor of the purple side.

I don't know what ohm reading the VSS should have out-of trans., but if you do have it out, verify there's a reluctor wheel inside.

Any 93-02 F-body or GTO 6 speed owner can loan you their VSS to rule that out. Aftermarket avail. of the VSS is a lot better than it was years back.

Getting closer...

MParks

Here's what came out, I tested the red wire at the cable X and it was getting 12.94v. Then checked at the green wire and same result 12 volts. Then checked continuity for both wires red and white from the cable X all the way down to the VSS wires purple and green to which they are hooked up to and they both have continuity

I also recently bought a VSS sensor a couple days ago brand new and put it in to see if that would change anything and it didnt. I couldn't see inside where the VSS goes but I could feel a gear in there.

MParks

Just a thought, would the wires from the VSS have to go through the ECM or the buffer box at all?

MParks

Got it working!! It was the ground from the VSS instead of the 12v power source. I just re routed the ground wire to the same location as the ground to which the cable X was running off of and boom it works. Probably because I was using the ground from the automatic which is why it probably didnt work. My new dip settings aren't right though it says im doing 80 in first gear so thats the next step

jmd

iTrader: (4)

In a stock third gen w/ ECM and cable drive speedo, the back of the speedo has an optical VSS which is wired to the ECM and cruise. That also means you don't have the buffer box that electric speedo third-gens (minus 90-92 w/ 7730 ECM) have. And that you don't need to change anything further with regard to VSS.

Good job keeping at it and finding your ground issue. Sometimes the dip switch settings don't make sense.