Flappy, Bouncy, Wacky Tachometer?!, Tachometer bounces back and forth while driving at constant speed Options

[vjb206]

Hi folks! First time/long time for me here in the Garage. I just purchased a '74 1.8 in Ohio and it died on me in PA on the way home to NJ. Right before it died I noticed this bouncy/flappy tach thing happening.

(IMG:http://www.914world.com/bbs2/uploads_offsite/media.giphy.com-23760-1677337178.1.gif)

As you can see my speed is constant, my throttle inputs steady – just cruising. However the tach is going nuts.

When the car died (in a rest area off I-80 in PA) it would turn over but not start. We ran some rudimentary diagnostics and remediation measures:

- Heard clicking/popping noise coming from driver's side of engine bay at speed, this was accompanied by the flappy tach phenomenon
- Generator light came on at some point while driving
- When flappy tach/popping noises would happen, I'd notice the car losing power for a split second
- Electrical systems stopped working during my drive (door open buzzer stopped working mid-way through the trip)
- Replaced the battery with a brand new one, no dice
- Power at the coil
- No spark at the plugs

Car is at a shop in PA - they will get to diagnosing it over the next few days. I'd prefer to fix myself, but I can't get it home from where it is without basic drivability.

Has anyone ever had this happen? Is the flappy tach a symptom of a larger electrical issue?


I found the post on adding the 2200uf capacitor to stop bouncing when changing RPMs rapidly, but I don't think this is that issue. Especially since the bouncy tach and the car dying are correlated (I think).


Would love to tap into the collective wisdom of the platform to help point me in the right direction.

[emerygt350]

What superhawk said. Something is shorting causing the miss and the jumping tack. Be careful, you don't want to go up in flames.