Tachometer needle jumps sometimes - cause?

[82DMC12]

I have not. If I had one I would test with it.

If you have the actron dwell meter it also does tach and volts. Unfortunately I don't know if a handheld tach is reliable way to rule something out since my tach jump did not occur on the actron but it did with the dash gauge. I think the actron has too much damping so it sent me down the wrong rabbit hole.

[Timeless]

UPDATE: Replaced the battery and alternator recently, about 3 months after the DPI engine mount ground cables. Tach jumping has reduced by ~90%.

[82DMC12]

UPDATE: Replaced the battery and alternator recently, about 3 months after the DPI engine mount ground cables. Tach jumping has reduced by ~90%.

Hard to say what the source is. I still had jumping even after a new battery and alternator! But I haven't had it ever since replacing the tach lead on the distributor and putting my old impulse coil back in.

[Jonathan]

I had been watching this thread previously because my tach needle fluttered a lot. It wasn't fluttering with the actual speed of the engine. It was just the instrument.

Over the winter, after seeing mention of the brown cables on the back of the alternator and that nut not being tight, I focused my attention there in the Spring before I got the car out. The nut I had on there wasn't staying tight. Too much wiggling possible with those cables pinched on top of each other. So I replaced that simple nut with an equally simple one, but this time I used a nyloc nut. And after 400+ miles so far this season, the needle has not fluttered a single time. So that was the problem for me. Those brown cables on the backside of the alternator were not maintaining good, solid contact.