basically, my car's speedo only works for about 10 min if its cold, and about 2 if its hot or sometimes not at all. the cruise works if the speedo works but it jumps around, up and down about 10mph. also im only getting about 10-12 mpg. im hoping this is just a faulty vss, but has anyone dealt with this before? or have any knew ideas on possible problems. any help would be appreciated.


1991 Z-28 Conv. 305 TPI
K&Ns, no muffler, jet prom, intake airfoil, 160 deg therm, mallory dist.

 

Stealth,

Welcome Aboard!

Are you getting a '24' DTC? Even if the MIL isn't on, scan for error codes to make sure. You may have a problem with the VSS or the actual plastic driven gear, or something different.

 

Vader is right on. Normally a bad speedo drive gear is the problem. Generally if the cable is dry the speedo will bounce around but unless it freezes in the sheath it will always turn. Don't know about the 91, my 89 has the vss sensor in the speedometer head itself. My cable was dry and shot so I ordered the cable and new sheath, ran the car for a week waiting for parts and it would throw a 24 code. Gas mileage went down a little because of ECM running in default mode. You might want to consider bumping to a warmer stat, 160 is too cold for these engines. Welcome to TGO, Danno 89rock, tpi 5.7, K+n, 180 stat, GM Perf. 3in. exhaust

 

right now, my car is only reading 2 codes, lean o2 sensor, and vss. it cant be the speedo cable because i dont have one, its electronic. but i dont know how to check the speedo gear thats attached to the vss.

 

91,

The VSS may be located on the transmission on your car. There is a simple clamp bolt that holds it in position. Remove the bolt, clamp bar, and pull the VSS out of the transmission. You don't even have to unplug it. Inspect the plastic gear on the VSS shaft for obvious wear. If it looks like a geriatric patient with his dentures out, it's time for a new plastic gear. Try to find any numbers you can on the gear, and note the color of the plastic (blue?). Take this data to the dealer and have them order another gear for about eight dollars. They may also need your VIN and rear axle data. Make a note of all the 'G' and 'M' codes on your RPO label before you go so you'll have the data they need.


As for the O² sensor, find a local parts store that sells Bosch or AC/Delco sensors and get a replacement it your's is more than 30,000 miles old. Check the electrical connections and wiring near the sensor when you change it. If your sensor is newer, check the connections and wiring.