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Tach needle started jumping suddenly

ConvertRider

ConvertRider

Member
I have a stock 1998 Dyna Convertible and one day the tach needle just started jumping up 8,000 while sitting at a stop light. Now the needle jumps around most of the time, at idle or while riding. I have the 6,000 rpm Screamin Eagle ECM, but it ran fine for years, and now just all of a sudden. Is there a way to test without the $500 speedo tester? Bench test on the tach?
 
Check the connections and if you don't find anything that looks bad, maybe try it on another bike or at least connect it to another motor with wiring to check the function. It's about the only way of testing it without getting into some $$$
 
Odometer is working, total and trip and the turn signals are fine. The bike is a '98, so I don't think there are any diagnostics built into it.
 
Sounds like a loose or bad connection somewhere. I'd start at the battery (it's the easiest to check) then follow the wiring back from the speedo.
 
Well, I have some other symptoms now. When riding, sometimes the engine misses when the tach jumps, sometimes not. Also, today when I started the bike in the dark, it turned over a couple of times, then everything went dead. I rocked the bike a few times and the lights came back on. When the bike started, the tach needle jumped all over the place. When it did, it looked like the headlight was flickering at the same time. Then, everything was fine, even after a few blips with the throttle. The tach was fine, but I did not let it idle long or ride it.

I cleaned the speedo sensor, it did not look that bad, not alot of shavings

Turned out to be a loose connection on the starter motor. Remember to check all 4 connections, not just the two at the battery itself.
 
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Glider, very true, but also because "the other end" is usually the one buried that needs 5 other things taken off to get at it: "--out of sight...out of mind"!!!
 
It only took me a few hours to figure out that after checking 3 of the 4 ends, taking the battery tray completely off 3 times and slowly assembling everything, that the problem occurred only when there was pressure on a certain area of the positive cable. I could create the problem by having a fully assembled battery tray and pushing on the cable a certain way. I traced the cable and found the 4th end, DUH !!!!

I am intrigued by how something so simple can cause a goofy problem like the needle bouncing, but then, I am not a mechanic, nor do I fully understand the workings of the bike, but I am getting better.
 
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