Daves03

Ok heres the deal,
1991 Chevrolet Camaro 305 TBI Automatic T-Top Red,
Speedometer and odometer dosent work, hasnt worked since the day i got it, the tachometer seems a pretty good ways off, im only idling at 2000 rpm more like 500-600 rpm, im getting a couple of codes stored, This code 24 for the Vehicle Speed Sensor Circuit Open, Ive heard of the Vehicle speed sensor itself, Ive heard of a little yellow box called a Speed buffer box, when driving the car the speedometer dosent move at all, If you listen very closely sometimes you can hear a tick at the back of the speedometer, Ive already replaced the Vehicle Speed Sensor thinking yeah thats it, I dont have access to a computer to connect up to the car or a Diagnostic Tool, SOMEONE PLEASE HELP ME, Please, Ive removed the dash panel on the passenger side and i have found the ECM, There is a brown wire and a pink/black wire running from the ecm to a silver box on the back side of the dash if your looking straight up the back side of the dash laying in the floorboard, im guessing this is the speed buffer but its not yellow, im guessing as well that this may be the brown wire and pink/black wires that i need to test on but i dont know, the wiring also goes through a double connector that was wrapped in some padding from the ecm looks like.

John in RI

iTrader: (167)

According ot the 91 shop manual the ECM is not the problem in your car. All 91's have an ECM that accepts the speedo signal from the sending unit then sends the signal to the speedometer and the Cruise system - EXCEPT for the TBI. The TBI set-up goes from the sending unit in the tranny - to the VSS Buffer - to the speedo ( and cruise. ) The ECM just reports that there is a problem in the system and doesn't actually relay the signal like in other models.

The VSS buffer should be mounted behind the dash on the passenger side. It will have 2 plugs leading to it,..... one with a YELLOW wire and PURPLE wire and the other plug will have Pink/black, Brown. tan, and red wires leading into it. The box should be yellow - but I have seen the case in a clear or slightly green coloer as well.



When you replaced that sensor did you replace the gear on it as well, or did you use the one that was already in there ?? It's possible the original "driven" gear had bad teeth and is not being turned by the drive gear correctly. Did you verify that the drive gear was still correctly installed on the tranny tail shaft correctly ?? I have seen the internal gear fall off the tail shaft before due to a bad retaining clip.... It's possible that this is your issue. You might also have a bad VSS Buffer - but it's really quite rare for thse things to simply fail.

If you find that you need a replacement buffer I sell them for $15 + shipping. I will also test it first to be sure it works.

Here's a copy of the 91 Camaro TBI speedo system wiring for you to review. There's also a flowchart to help you test the system. Good Luck !!

NowTheBadNews

iTrader: (3)

take a drill and spin the VSS sensor with ignition on that will help finding out where the problem exists.Pretty simple if it works with a drill then the vss drive gear disintegrated. if it doesnt work then it's the vss or the buffer or speedo itself. Just easier narrowing it down with a drill.

Daves03

thanks for everyones help so far i really appreciate it.

Daves03

yes i moved the old gear from the old speed sensor to the new speed sensor, the speed sensor had a hole drilled in the shaft then the gear was installed and i cant rememeber wether or not it had a bolt or a pin or something in the hole, i did not check to see if the gear was on the tailshaft of the transmission that is a good idea, but first im going to use the chart you sent me and take a look at the wiring because i believe everything is good down at the transmission, thank you.

camaro_ABN

i think im having the same problem..i slammed on my brakes pretty hard in rush hour traffic and i heard a loud clunk sound and my speedo didnt work....let me know how the vss change goes cuz im looking it in the face right now.

redlsed88

Im having the same issue the tach is a common problem not related to the vss buffer, if you want to keep the oem cluster than there is a resistor you can solder in, do a search on that there is plenty of good info on it. The speedo however sounds related to buffer. I swapped my cluster out with the nordskog digital dash and im going to try to replace the vss buffer with the dakota digital sgi-5 universal interface. it looks like it does the same function as the vss buffer. I guess well see how it goes

Daves03

tested my buffer it seems to be ok, the signal is not reaching the buffer box from the yellow and purple wires at the vss, removed the speed sensor and rechecked the internal drive gear on the transmission, drive gear and driven gears are ok, the vss is spinning but not sending signal through the purple due to bad wire, the yellow wire is reading .1 ohms.