Contents
What does it mean when your tachometer jumps?
Usually a loose or failing switch will also cause the car to run poorly, but if the problem is very minor it can begin as an erratic tach signal. Look for corrosion, a broken wire, or a loose connection anywhere between the coil terminal and the tachometer.
Why is my car dying when I come to a stop?
If your car stalls when you come to a stop, it could simply be a dirty air filter. The air filter may have become so clogged that not enough air can pass through it to the engine. An air starvation problem in your engine could also be caused by a mass airflow sensor.
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.
Can a loose kill switch cause erratic tach signals?
If your kill switch is in the negative side of the battery circuit (interrupting the ground), check the switch and its connections carefully. Usually a loose or failing switch will also cause the car to run poorly, but if the problem is very minor it can begin as an erratic tach signal. Fixing the problem now could save you a race later on.
Why does my spa tachometer fire randomly at idle?
Since the spikes are random, they confuse the tach into bouncing up and down, usually reading higher than the actual RPM (but almost never by a constant factor). 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.
Can a bad pickup coil cause a bad tach?
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.