I have a 1992 Chevrolet K2500 4 Wheel Drive. I recently had a new motor installed. The speedometer started to fluctuate about 3 days after getting it back. At 45 mph it will peg out at 80 mph and return to speed. However at 65 mph it will peg at 80 mph and either stay or return a few seconds to 70 mph and then up to 80 mph. I am not getting a engine light. While removing the motor, the cable going from the TBI to the Cruise control was broken and it is currently disconnected from the TBI. I noticed that if I hit the resume speed or set on the cruise control handle, the needle fluctutation coincides with that. Should I pull the fuse on the cruise control? Any suggestions.
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The speedometer can fluctuate rapidly under normal driving conditions when the car's speed changes abruptly, but sometimes the needle can start swinging around the dial without any fluctuation in speed. If the hairspring comes loose or breaks, it can't hold the speed cup in place, and the result is a fluctuation in the dial. In electrical speedometers, if the circuit that counts the magnetic pulses fails, it can cause the speedometer read-out to vary from the actual speed and to shoot upward or downward without notice. If a speed sensor in the automatic transmission starts to malfunction, it can affect the speedometer and cause fluctuations. In these instances, either the speedometer or the sensor needs replacement.
The speedometer and odometer gets a signal from the speed sensor in the side of the transmission where the speedo cable once was. The problem could be the speed sensor, or something in the wiring, or in the instrument cluster. Or it could be that the transmission is failing internally.
I had the same problem, if your car is rather new model, what I mean is if it is mostly electronics than this is a problem... Lights that go on and off is indication of a short somewhere, if this is caused by a ground wire being loose than the problem can escalate to more serous problem... like burning of components, what happend in my case is there was a loose ground wire, this burned out my ignition, the ignition made all the electronics shut down, including head lights at 9pm in the evening...
Turns out this is a common problem for the Rendezvous. I took it to a mechanic and after he tested to see if all the speed sensors were working with his handheld computer reader, (because there is no speedometer cable anymore) He reset the needle by turning the key about 25 times as far as possible without starting the vehicle. The speedometer needle came back a bit each key turn till it reached zero. It's been working fine since.
either a bad spedometer cable on these older cars the spedo cable can be lubed with a special adapter and a special grease in your grease gun or the cable removed from the case and lubed OR the spedo head is tired and needs to be rebuilt
The speed senser is mounted on the transmission. This device is an slocrto magnatic motor and they cost less than $100 there held in with one bolt and have an electrical connector. Many times if it's bad enough the check engine light will come on. This problem but the heating up but work OK cild is a good chance the senser has failed.. The trans mission should be checked for overheating as the senser failure will be heal related