Speedo bouncing, then dead, then working, then dead

L

LensWork

New LVC Member
Joined
Aug 6, 2011
Messages
7
Reaction score
0
Location
Orlando
I have a '94 Mark VIII that sat for a couple of years while the air ride was down. The last few months when I would start it during the down time, the speedo would bounce all over the place while just sitting still. I had the air ride replaced with coils last weekend, and the speedo would not work when I took it out for a test drive. Then on my second outing, it started working after about a mile. Then today it stopped working, and then suddenly came back to life. It will still bounce (0-20-10-60-0-40-0, etc.) when sitting still. Any ideas/suggestions? (PLEASE) :confused: Thank you!
 
Make sure the back of the spedo has not become loose making the needle hit the back.

You might have to take the spedo out and re attach the backing plate " the part that has the mph on it."
 
I would suspect the speedo sensor on the trans is bad. If I recall, pretty easy to replace and not expensive. It has small gears, they can go bad.
 
LensWork said:
the speedo would bounce all over the place while just sitting still.
Click to expand...

unity said:
I would suspect the speedo sensor on the trans is bad. If I recall, pretty easy to replace and not expensive. It has small gears, they can go bad.
Click to expand...

this would suggest the speedo moves while the car isn't moving? if so, i really doubt its that little gear, and lean more toward wiring.
 
New one on me too. I would guess wiring or possible solenoid going out or has went out. A wire might be grounding on something it shouldn't be. Could also be computer related but not sure on that one.
 
i also am thinking wiring.
on the computer, i don't know what, if any, electronic modules control the tach.
 
maybe.
although, with as many bad alternators as i see come through here, i would expect that to be a more common symptom.
 
87TTOPGT420 said:
Defective cluster???
Click to expand...

my 2 cents. you could test the voltage coming from the harness going to the spedo to rule that out. and at the trans sensor as well. I would think that the trans sensor would be the easiest to access.

if the voltage jumps at the sensor then you know it is the sensor, you will have to tap into the harness somehow as it has to remain plugged in in order to recive voltage. if it does not jump at the spedo harness then you know it is the spedo. any signs of mice? my car sat for like 5 years before i bought it and it was ravaged by mice... sucked BAD!!!
 
Thank you for all of your suggestions. Based upon your ideas, and those from other similar threads that I have read, I can eliminate a couple of possibilities. There is no sticking of the needle due to interference with the backing of the gauge as the needle moves freely (bounces) even with the car not moving. The tachometer and the other gauges work fine (except for the odometer, which of course does not work when the speedo is not working). The car has a new (replaced a few weeks before being parked because of the air ride) alternator, so that is an unlikely cause.

I am hoping that it is as simple as replacing the VSS. If it is a wiring issue, I know that can be a bear to track down. The really strange part is that the issue did not present itself until recently (the last few months). As I said, the car had been sitting since the summer of 2009, and just in the last few months when I would start the car to keep the battery charged (about once per week) did the speedo start bouncing, all while the car was just sitting still in park.

Am I correct in assuming that the speedometer is electronic, and not cable driven?
 
You must log in or register to reply here.

Members online

Total: 384 (members: 2, guests: 382)
Back
Top