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Discussion Starter #1
Just acquired the cycle from auction with no history. Runs and rides fine, but the speedometer is going crazy. Sitting still at idle it shows 1 or 2 mph - with choke, it dances between 0 and 150 and constantly refreshing all over the place.
Below is a video showing this behavior. Don't know where to begin to diagnose the issue, and don't have a service manual for the bike yet, if anyone has PDF.
Thanks!
 

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What your bike has is a hall effect sensor which is mounted in the rear caliper mount bracket. There is probably an issue with one of the wires, Either it's almost broke (getting signal part of the time) or one of the wires are shorting to ground. I would trace the wires from the connector at the sensor whip all the way to the fuse panel after I tested for continuity between the connector and the fuse panel terminal. As you're testing the continuity jiggle the wire loom along the way and that may narrow it down. The wires should be white/red, green for ground and black/violet. All of your sensors go to the same place in the fuse panel which (according to my drawing) should be a terminal strip. I doubt the sensor is bad unless you see some physical damage to it. I will try to attach pics with the location of the sensor and a pic of it in the electrical schematic.
978349
978350
 

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In the same forum you posted this in we have a large collection of service manuals
on post #17 you will find what you are asking for I just tested the link it still works.
 

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Just Visiting Your Planet
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I just tested the link it still works.
I hope so! ;)
 

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Discussion Starter #5
Kenny, thank you kindly for the help. I'm making progress but still stuck.

I have used your information, along with the service manual, to test for continuity and voltage at the 3 wires which go into the speed sensor. By disconnecting the speed sensor, and checking on the harness side for continuity & DC voltage, I have found that I do not have ground at the green wire as you suggest, if it is indeed supposed to be ground - the diagram I have (and your picture) labels green as "BODY 24 (VHSPD)". I previously had but no longer seem to have ground on black/violet "ENGINE 20 (SNSGND1)". I'm going to poke around the harness to see if I can ensure black/violent regularly see ground.

For voltage, I have 5 VDC on white/red, and between 1.6-1.9 VDC on green with ignition key on - both drop voltage with key off.

What I am unsure of is where all 3 of these wires go after they leave the speed sensor and enter the main harness by the intake. I very very carefully read and reread through the electrical section showing the wiring looms in the service manual, but they just show the wires joining into the large harness near the intake ports, where the wiring routing pictures stop showing the direction/location of routing.

Do these speed sensor wires all head to a fuse, as you suggest? Do they go to the ECU first, or to the speedometer first? Do they change color?

I don't expect someone to do the diagnosis for me of course. A bit of direction on precisely where the wires go for this circuit, and what voltage they should have and when are questions left unclear by the service manual.

Best.



What your bike has is a hall effect sensor which is mounted in the rear caliper mount bracket. There is probably an issue with one of the wires, Either it's almost broke (getting signal part of the time) or one of the wires are shorting to ground. I would trace the wires from the connector at the sensor whip all the way to the fuse panel after I tested for continuity between the connector and the fuse panel terminal. As you're testing the continuity jiggle the wire loom along the way and that may narrow it down. The wires should be white/red, green for ground and black/violet. All of your sensors go to the same place in the fuse panel which (according to my drawing) should be a terminal strip. I doubt the sensor is bad unless you see some physical damage to it. I will try to attach pics with the location of the sensor and a pic of it in the electrical schematic. View attachment 978349 View attachment 978350
 

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I have had this same issue for years. I’ve replaced the main wiring harness, and the pick up at the wheel. It shows itself more when the bike is running warm. But will also sometimes jump when I put up the kick stand. I have learned to know the speed I’m doing via the gear and RPM.
 

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there was an 848 locally that had a wacky speedo issue. i put an ecu in it, that didn't help, and then the guy bought another dash so needed a immo disabled ecu in it, which again didn't help. he bought a s/h loom and had someone else fit it and that didn't help. a local dealer eventually worked out it was a bad coil. new coil, fixed.
 

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Discussion Starter #9
Just so I am abbbsolutely sure of what you're saying, an Ignition Coil was found to be the solution in one instance? So perhaps I throw a pair of ignition coils at the bike and see what we get?

I've been trying to test using a different dash, but I can't seem to find what software to use for the ECU flash purpose of disabling the immobilizer, and thus attempt use with secondhand dash.

there was an 848 locally that had a wacky speedo issue. i put an ecu in it, that didn't help, and then the guy bought another dash so needed a immo disabled ecu in it, which again didn't help. he bought a s/h loom and had someone else fit it and that didn't help. a local dealer eventually worked out it was a bad coil. new coil, fixed.
 
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