I have a 1990 Grand Marquis and it has an interesting "glitch", as soon as I turn on the key, the speedometer needle jumps to 20 mph. While driving it seems to work OK (it appears to indicate a little slow, e.g. 60 mph indicated = 70 mph GPS) and every time I come to a stop, it still indicates 20 mph. This isn't crucial, just irritating at times. Any thoughts on this? Thanks in advance.

Gregg

 

P.S. I checked the search functions in both this category and the General Tech category. I didn't find anything like this in either of these areas.

Gregg

 

as for the 60=70 issue, check the tire size against the tire information plate on the door wall (right rear on my car). Tires different from stock will give wrong speed readings.

Not sure if they changed the speedo in the 90 from the 88 I have, if so, ignore this.

Sounds like the spring on the speedo may be in need of some greese and may be a bit sprung. With mine, all it needed was to take the needle and re-zero it.

If you have an electronic speedo this part may apply.
You may have a blown resistor in the speedo itself that may require replacement.

 

Thanks,
Tire size was correct when I took the readings but they were in bad shape. I have slightly taller on there now but haven't checked to see if it is still off, maybe this week. Forgot to mention that the speedo needle is at zero when the ignition is off but moves as soon as it is turned on. It is an analog style, but it may be electrically controlled. I don't think it is 100% mechanical. I will get into the dash when it warms up a bit here, hopefully that is before May.

Gregg