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1981 Mercedes 300sd
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29 Posts
Discussion Starter #1
When I purchased my 81 300sd 6 months ago the dealer installed a new tach amplifier. Every so often get the needle would bounce a bit but alway stabilize. It now will not move unless the engine is under high throttle. When I let off the throttle it stops working again. I recently put in a new alternator and voltage regulator. What else could be causing my tach issues? It seems power related? Thanks in advance for any help you can provide.
 

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300SD
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11,191 Posts
You can have a bad/contaminated magnetic sensor at the crankshaft dampener pulley. This is the sensor that sends the signal to the tach amplifier.

You may want to clean the head of the sensor first - could be contaminated with grease.

Also, check the connection from the sensor lead to the tach amplifier.
 

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Registered
1981 Mercedes 300sd
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29 Posts
Discussion Starter #3
You can have a bad/contaminated magnetic sensor at the crankshaft dampener pulley. This is the sensor that sends the signal to the tach amplifier.

You may want to clean the head of the sensor first - could be contaminated with grease.

Also, check the connection from the sensor lead to the tach amplifier.
What does the "magnetic sensor" look like? Is it easy to get to?
 

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2013 MINI Copper S Clubman, '84 300CD-weekend car
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10,152 Posts
What does the "magnetic sensor" look like? Is it easy to get to?
Follow the gray wire from under the tach amp. It leads to the magnetic pick up. Hard to get to, but you may be able to spray brake cleaner on it. It reads a stud mounted on the crank pulley.
 
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