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Here is a strange thing I have not encountered before. When I turn the key to position 2 (ON) it's normal. When I turn key to position 3 (START) the odometer begins turning as if you are driving 65mph down the road. When I let the key back to position 2 it stops turning. The car does not run, so I do not know what it will do when running. Didn't notice the speedometer turning even though the odometer was.
Anyone ever run across that before? How does the odometer operate on an 86 XJS? My current guess is that the odometer is driven by an electric motor and there is probably a wire making connection where it shouldn't be... thanks!
Did you ever figure it out? I have an early '88 that does the same. I am reworking everything on it and have not got to the point where I need to start her up yet. Strange, my speedo drive is different than yours as well. Good luck!
Hello. Its an interesting problem and I can only offer a suggestion...
I had my instrument cluster out the other day for cleaning and a general inspection. The car had been sitting for some time and water was an issue. PO was a dumb ***... Anyways, after the cleaning, when I plugged things back in and supplied power with key turn, things turned on and seemed fine. When I turned on the lights, things went a little batty. None of the gauges worked, with lights on - actually they all maxed out. Tach, on the other hand, went from normal to dead... Turn lights off,,, things go back to "normal".
I grabbed the cluster, which was still not tightened down, and when I touched it with lights on, things went back to "normal". Hmm. I released the cluster, the thing went batty. What I learned was across the top of the ICluster is a long flat metal strip/bar. It is a common ground at least three spots connected to the ribbon type circuit with small screws. I again removed the cluster, took a Dremel and cleaned connection spots to bare metal. Reconnected, reinstalled and voila',,, a simple ground issue...
Its an old technology... I would take it out (CAREFULLY) and inspect. Clean. Check. My guess would be that the problem lurks in there. Although old tech,,, inspection is pretty simple and just really look closely for something "out of place". What IS supposed to be there, is pretty obviously supposed to be there - if something is amiss, that is kinda obvious as well. But you really just have to slow down and look. If I were to take a guess at a PLACE where the ribbon split/opened and/or the two faces of the ribbon separated and came apart,,, the copper filament from one system is touching/contacting another (your odometer spinner)... The whole front transparent section of the cluster also comes off (see photos), allowing you to access the inside of the cluster from what IS its "front". Seeing the connections of all gauges, the speedo and odometer from the front - basically copper plates where contact is made with a screw connecting the back ribbon to the gauge plate which relies on the screw coming thru the back of the cluster and "rubbing into/upagainst the gauge plate (weird set up - you'll see).... Then, there are three small nutts on the back of the cluster (i think its three) holding the OD in, making three more connections with the ribbon circuit on the back, thru to three OD 'studs' that run the OD. Kra kra ---- Good luck.
Agreed on poor grounds causing all sorts of strange behavior. I remember the tachometer on my XJS would go crazy whenever I turned the headlights on. Cause: poor ground.
As to the spinning odometer:
'Tis a bit odd that the odo would turn but the speedo needle itself doesn't spin. I can't explain it. ....at least not on my first cuppa coffee and probably not on my fourth, either
However.....
Do check connections and grounds.
It isn't at all unusual (on any number of cars) for the *speedometer* to spin-up while cranking if the supply voltage is low....or if the connections and grounds are poor. I've seen it many times over the years and just went through this myself on my '85, actually.
Ha ha I have this fault as well and had just done a post on it. I don't know when you say car not running you mean won't start as mine won't and in addition to not starting the mileage odometer is going round and the speedo goes a bit nuts during cranking the tacho goes nuts as well a d had disconnected that from amp feed and still the same. . I removed the transducer connection that pulses the speedo and odometer. Dependant on age of car is location of transducer mine is on gearbox on 87 but later models its on the diff.
Its only during crank for mine this happens. Whilst I have not worked back from binnacle to see where pulse is coming from yet, it only happened after I removed injectors.
I have found a crack on side of dizzy cap and I am thinking as the crack is on retaining screw the spark is grounding possibly on the screw causing my non start and also pulsing the odometer and speedo.
The only other pulse would be from amp when cranking. Ordered new cap so I will have wait and see. I wouldn't have thought poor grounds on back as that would stop it moving at any time I would say you have feedback through the ground.
My next move if not cap it to put a node light on feeds to speedo and see if it pulses in time with injectors etc.
10-12-2017, 03:50 PM
Odometer spinning when starting engine...?
