The old bouncing tach, 82 SC
09-20-2006, 10:04 PM
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The old bouncing tach, 82 SC
We've all heard about the bouncing VDO tach, and I've had it myself occasionally. It usually only lasted minutes and went away for months at a time.
Today it lasted for about 5-10 minutes on the way to work, and I decided to stop the car, kill the engine for about a minute, then restart, to see if anything changed. The tach was still bouncing when I killed the engine.
When I tried to restart, I got a week grunt from the starter as if the battery was very weak, and that was it. I checked the battery for loose connections, then poked arounf the engine for anything out of norm. Nothing.
After a few calls to arrange for a lift the rest of the way to work, and several attempts to restart, it finally fired up as if nothing ever happened. Elapsed time less than ten minutes. It started bouncing a few minutes later, then stopped, and the remainder of ride was uneventful. It started just fine and was perfect all the way home from work at the end of the day.
Those are the clues. What happened?
Today it lasted for about 5-10 minutes on the way to work, and I decided to stop the car, kill the engine for about a minute, then restart, to see if anything changed. The tach was still bouncing when I killed the engine.
When I tried to restart, I got a week grunt from the starter as if the battery was very weak, and that was it. I checked the battery for loose connections, then poked arounf the engine for anything out of norm. Nothing.
After a few calls to arrange for a lift the rest of the way to work, and several attempts to restart, it finally fired up as if nothing ever happened. Elapsed time less than ten minutes. It started bouncing a few minutes later, then stopped, and the remainder of ride was uneventful. It started just fine and was perfect all the way home from work at the end of the day.
Those are the clues. What happened?
09-20-2006, 10:58 PM
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The first thing I would do is make sure the battery connections are clean and tight, including where the ground strap bolts to the body of the car.
It could be a failing alternator/regulator. Here is more:
If the alternator and the voltage regulator are working correctly, the voltage at the battery should read 13.5 to 14.5 with the headlamps on and engine at 3000 RPM. Here are some of the symptoms of a failing alternator:
• Battery voltage too low or too high
• Battery boils over
• Alternator warning light stays on
• High or erratic idle
• Slow operation of wipers and windows
• Bouncing or erratic tachometer needle
• Hesitation on acceleration
• Overall sluggish, poor performance
It could be a failing alternator/regulator. Here is more:
If the alternator and the voltage regulator are working correctly, the voltage at the battery should read 13.5 to 14.5 with the headlamps on and engine at 3000 RPM. Here are some of the symptoms of a failing alternator:
• Battery voltage too low or too high
• Battery boils over
• Alternator warning light stays on
• High or erratic idle
• Slow operation of wipers and windows
• Bouncing or erratic tachometer needle
• Hesitation on acceleration
• Overall sluggish, poor performance
09-22-2006, 02:16 PM
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the bouncing tach
I HAVE noticed some slight dimming/brightening of headlights at night (very slight), but except for the bouncing tach, none of the other alternator symptoms. I wonder if that may point to the regulator, then?
And long term, no problems cranking or starting.
Thanks
Paul
And long term, no problems cranking or starting.
Thanks
Paul
09-22-2006, 07:36 PM
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Hi Paul,
The alternator/regulator seem to be "married" in my experience. When I have replaced one but not the other, I'm usually back in there again fairly soon. It's a fair amount of work, so you may want to just replace both.
The alternator/regulator seem to be "married" in my experience. When I have replaced one but not the other, I'm usually back in there again fairly soon. It's a fair amount of work, so you may want to just replace both.
