What causes a tachometer needle to jump around?
Despite their simplicity, an electronic tach or shift lights can sometimes behave strangely. A needle that jumps around and shift lights that fire at random may look like a huge problem, but in fact they are usually caused by a simple issue that is easy to fix. First, let’s narrow down the symptoms.
Why does the tach needle keep moving up and down?
The tach needle bounces up and down instead of holding steady. If you hold the engine at a constant speed, the needle continues to move around. Shift lights fire at odd times, usually long before redline.
Why do shift lights fire randomly on my tachometer?
Shift lights will fire randomly, sometimes even at idle. SPA tachometers seem to be particularly sensitive to these spikes, but Auto Meter and Stack tachs seem to be much less affected. The fix is to add a simple 47k Ohm resistor (1/4 watt, 5% to 10%, rated to 500v) in the RPM signal wire from the coil to the tach.
What to do if speedometer needle jumps up and down?
Reach around behind the speedometer or remove the instrument cluster to gain access and disconnect the speedometer cable from the speedometer. Pull out the inner cable, clean and inspect it, coat it with light grease, or M/C cable lube and put it back together. That should cure it… The speedo cable for those old cars is like a spring.
Despite their simplicity, an electronic tach or shift lights can sometimes behave strangely. A needle that jumps around and shift lights that fire at random may look like a huge problem, but in fact they are usually caused by a simple issue that is easy to fix. First, let’s narrow down the symptoms.
Why is my tach jumping all the time?
If the problem is only with the tach and you are not having trouble with miss firing, bogging, etc. the problem is probably in your tach or the wiring to it. A bad pickup coil will cause erattic tach behavior but will also cause erratic missing, bogging, engine dieing while idling, and other various ignition related problems.
Why is my tach jumping on my MSD?
A bad pickup coil will cause erattic tach behavior but will also cause erratic missing, bogging, engine dieing while idling, and other various ignition related problems. An MSD uses the same pickup coil that your stock ignition system uses so the procedure is the same. Ludicrous speed, GO! I had a similar problem with the tach in my 73.
The tach needle bounces up and down instead of holding steady. If you hold the engine at a constant speed, the needle continues to move around. Shift lights fire at odd times, usually long before redline.
Why is my tach jumping at 5000 rpm?
I put my MSD box and my Auto Meter tach and speedo in and mine kinda does the same thing… when first started the needle jumps about 2000 rpms and then goes away when it warms up a bit. Also, at about 3000 rpm it will jump around 500-1000 rpms.
Is there a way to fix a bouncy tach needle?
Some ignition systems are electronically noisier than others. While proper grounding of the tach and routing of the signal wire go a long way towards preventing this, sometimes it’s not enough. Follow along with the AutoMeter crew as we remedy this problem. NOTHING besides the steps we took in the video was done. The results are 100% real.