Ok so the Corvette I bought a month ago has the speedometer and odometer not working. Tach, oil pressure oil temp water temp all fine.

Had someone look it over the vss motor in the transmission had a wire off I soldered it back on, vss back in the transmission no speedometer or odometer. Gas guage isnt accurate below halfway not sure if that has anything to do with it.

From what I read the vss sends about 4000 pulses per mile out.

What Im thinking about doing is pulling the dash and add a couple of wires from wherever the vss signal enters there, so I can check it with a voltmeter while driving.

Maybe even build an electronic frequency counter that would display the MPH and create a signal to control the odometer.

If I had an odometer with a motor outside the circuit it would be nice, theyre a bit pricey on ebay at $34 shipped. Anyone have one theyre willing to loan out for the information or sell cheaper? Or know where I can data on driving the odometer motor?

Its important for me because my insurance company gives me a decent discount if I drive not so many miles, but with the odometer not working I dont see how that can work or if its even legal to drive it that way.

The other issue is, if I do design and build an electronic replacement for the speedometer, what about engine control? I assume right now its running in limp mode? Will it hurt it?

By the way there is a two pin connector hanging down from inside the dash by the IP, with a pink and a white wire. It hangs near the brake pedal. Anyone know what it is if its part of the IP?

 

1984

 

Your car has 2000 pulse output from the VSS to the dash cluster which then continues to the ECM ( computer ).
If you have no VSS input the ECM should be displaying a code 24; no VSS input.
(Also exhibits as engine problems like stalling when slowing down)

Pull the codes and see if anything present
http://www.corvettephotographs.com/c4vettes/codes.htm

If it doesn't have a VSS code then your VSS is working fine and the problem is with the speedo unit itself

 

If the VSS is not transmitting a signal, your torque converter (if an automatic transmission) will not ever lock up, as the ECM needs the speed signal to command the toque converter lockup above a certain speed.

That will mean a softer throttle feel and more heat being craeted in the transmission.

Jim G

 

It seemed to run ok even when it had only one wire from the vss motor. Well, the idle is a little erratic until it warms up at least. Sometimes when it starts it idles at 1200 sometimes it wants to drop below 400. Seemed to shift firmly though.

The check engine light does come on once in a while, OReilly said they cant pull codes from pre 90 something cars I didnt check who else could yet.

What about that small 2 wire connector? I would upload a picture but cant find the manage attachment button when I post.

 

I thought an 84 was a 2 pulse square wave?

 

I`ll give this a try tomorrow and post back what I get.

 

Nope. The only two symptoms I detected when my VSS was not transmitting were no torque converter lockup and my FX3 suspension also showed an error, as it needs the VSS signal to alter its settings with speed changes. I did not get any of the other symptoms.

Jim G

 

OK I found this aldl connector it has metal connectors in slots 1 and 2, 4 5 and 6 on the top (left to right)

At the bottom I think just 1 and 2

So I guess connect pin 5 and 6 the last two on the right at the top

And turn the key to the first stop, or the second one where the ip lights?

 

More things to add to the list of VSS problems:

The torque converter will not lock. The ECM uses the VSS signal to decide when to lock the TCC.

The ECM will not turn on the upshift light if you are in Drive (auto). I assume there will be a similar problem with the manual transmissions.

 

Mine is an automatic. In another thread I was informed theres a gear missing from my vss sender and that one for an 84 wont be easy to locate. Im driving it the way it is, but thinking about looking for an 85 or 86 vss with the gear on it, and use some type of converter between it and the dash.

Another thing Im thinking about is a lock up switch. I think some people use some kind of switch to control that for certain mods?

 

Since this thread started I have learned that 84 thru 90 are all the same (except gears) and output a 4 pulse sine wave. There's two units one is white and another is black I think. If you're lucky WVZR-1 will chime in with more.

 

The VSS's are indentical in operation.
The difference relates to what speedo driven gear they take.
One is for 39 -40 tooth gears , the other 41 -45 tooth

 

You only need the gear , not a complete VSS

If they remove the computer and use a carb
With the computer lockup is done automatically with no driver input ( assuming the VSS is working )

 

This is "Toni's" other thread regarding the VSS. I've mentioned to her in this thread what's required OR how I'd proceed if it were mine and I've done a few hundred maybe speedo/odo calibrations.

http://forums.corvetteforum.com/c4-t...57-84-vss.html

Many in this thread have commented there also and if there's something that anyone feels has been left out use either thread I'd guess to help.

I tried to respond to this thread a couple hours ago and the CF wasn't available from my ISP at the time. The last two posts were done after I attempted.

It's my understanding that the connector is burnt off or broken off and Toni mentioned that she thought her VSS presently is white (with no numeric information) and that it also doesn't have a gear on it. All '84 Corvettes used the same VSS as factory equipped with only the tooth count changing for ratio. There's no telling what hers is without confirmation. A "service" VSS for an '84 would be "black" - as difficult as the VSS is to obtain and the gears also I suggested a "start from scratch" - the car is "new to her"!

I believe everything in the other post was understood by Toni and are the least expensive and proper effort to correct her problem.

Toni - rather than just buy something and assume it would make it work and THEN add another "BOX" to correct the error. If you're driving it as it is - return to the last fellow that had the VSS out and using the method I described in the other thread calculate the rear axle ratio, while in the air maybe remove the VSS again and see what color the drive gear is. With that information and the tire size your search could continue for the correct parts to correct it. If you use just any VSS, gear combination and want to use another "box" to correct it I'd guess you've added $100+ and another operation to the fix.


I likely have NOS parts to fix it BUT they're not inexpensive. If you'd like to try a less expensive route I understand and I hadn't attempted to sell you anything - just to help fix it right with the least aggravation. I've done the same for many.

 

He's raising his post count ?

 

You posted while I was retracting that comment BUT I did make it!

 

I'm good on the post count. Finally made it to 4000, so I have 5 red stars now. ;-)

I was searching for something else and found the old thread. Sometimes I post to add info for people coming along later, even though the original problem was fixed long ago (I hope).

I didn't remember seeing the lack of VSS signal causing the TCC not to lock, so I added that.

My cluster is in pieces all over my desk right now because it's showing zero MPH all the time (except when it's cold -- that's weird). I traced out the circuit but I need to get out the 'scope and signal generator to see where things are going wrong. There's a special IC for the speedometer function with a GM part number on it. Who knows where that came from. It's probably a custom chip with no possibility of replacement after all these years. The batee.com web site has a cluster schematic on it but the lower right corner is missing. Guess where the speedometer circuitry is.

I know the VSS circuit is good because I measured 435 ohms on the cluster connector, so it has to be inside the cluster. I already drowned the connectors with contact cleaner, so I don't think that the problem is in the connections.

 

added vss info,


ok guys to put to rest the later vss in the early cars. My car a 89 z51 354 gear had a moron replaced the black tag with a blue tag and not change the vss over between the two. So I ended up with the wrong late vss and wrong connector to the vss (early connector). Suprisingly the connector slides in but does not lock.Its a miracle but it stays put. The vss output is read by the 84-89 digital dash. No problem at all. All that needs to be done in this situation is change the connector. Now did I find a early vss on the loose after beating my self to death finding one and a black tag trans later with vss yes. I will install the vss in the blue tag soon as I will not cut my wiring.Black tag is for later down the line. For the guys that dont care put the late vss in for low gear conversions finding a early black vss is to much of a pain.Just change your connector. Or get in line my vss late will be for sale lol.

 

This should be a stand alone thread, so others may benefit.