Speedometer issue..

[Iceman8.6]

Have this posted on TCCCoA then got a "We've all moved to forum dot bird cats dot com" PM. Had forgotten about that so will copy and paste from TCC:

: 1997 TBird- 4.6l with all stock drive line..317,000 miles..

The speedometer has started going to zero when driving then returning back to the correct speed after a second or two..the car does not downshift or hesitate and the rest of the gauges on the cluster act normal and do not move.

Is it possibly the speedometer is wearing out / going bad? Used the search function and the VSS was brought up as a possibility.

 

[Grog6]

most likely.

 

[Iceman8.6]

most likely.

VSS or speedometer or both? Does the 4R70W only only have the VSS or does it also have a OSS. Thanks!

 

[Grog6]

vss only. The 97 speedos rarely fail.

 

[theterminator93]

I disagree; if the VSS signal from the trans was dropping, the PCM would see and adapt by changing gears and also likely throwing a DTC.

IMO it's most likely a connection going bad between the cluster and PCM. If you have an OBD-II scanner or Bluetooth adapter and app for a smartphone you can verify this by watching the vehicle speed directly from the PCM; if it doesn't drop when the speedometer goes to 0, it's a connection issue or bad speedo. If it does drop then I stand corrected, and it's a VSS or connection issue between the VSS and PCM.

I have seen at least one bad speedo out there (one of the 150 MPH SHO speedos I swapped in did exactly this until I swapped it out for another).

 

[3_97_Sports]

One of my 97s does the same thing, it started after I put a purple speedo gear in.
I also put new pi heads on it at the same time, and got a tune.
I am not sure which one of the above caused the speedo issue
I haven't really driven it since then, as I was sold a shitty tune, and it doesn't run right. He gave me a tune, it pinged like shit, I told him about it and he adjusted it for ethanol in the gas, and it pings twice as bad now. Undriveable really, I can make the valves clatter at will with the gas pedal.
I am going to start my own thread...
But yes, my speedo also drops out randomly without it affecting the shifting.

 

[KevinVarnes]

I have a bad speedo in an '89 SC I am working on. It kind of goes up and down randomly. I verified it with another speedo that worked fine. When the VSS connector on the '97 failed it would shift erratically and stall at stops. Good time for you to upgrade to the SHO 150MPH speedo.