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Old 03-24-2008, 01:37 AM
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Question 1984 300D Tach Intermittent

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I am having problems with my 300D Tach. It is intermittent. Acts like a ground but I don't know. Tach reads fine at times then 0 at times no rhyme or reason to when it decides to read.

Recent work done at independent repair shop. Trip odometer repaired plastic gear was broken also replaced bulbs and rheostat in gauge cluster. Same trip in had new A/C compressor put in as old one was shot also put in new A/C control unit as temperature control was broken and would not turn.

Tach problem started after this work was done..... Any pointers to look at would be much appreciated. Checked tonight and my car is not eligible for the cigarette butt trick. Amplifier is a plug in to read diagnostics.

Florida 1984 300D & 2002 C320 Sport Wagon
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Old 03-24-2008, 01:48 AM
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0-60 in 10 minutes flat
Join Date: Sep 2006
Location: Middletown MD
Posts: 527
Your tachometer's engine speed sensor is mounted on the rear of the engine (Left Hand side) on the bell housing. It should be near the back of the oil filter housing.

The mechanic probably jarred something loose while working inside the dash. There is also a two pin connector that may have come loose. Find the engine speed sensor and follow the wire back to the firewall - make sure that connector is tight.

Here are is a thread...
Figured out why my Tach won't work
1984 300TD

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Old 03-24-2008, 12:49 PM
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Join Date: Mar 2008
Posts: 3
Thank you

Thank you very much for your insight and quick reply.

I will get out this afternoon and check the wire from the sensor back up to firewall. I agree on the loose wire under dash but want to rule out mechanical/connection issues before I run it back to the shop for them to square away.
Florida 1984 300D & 2002 C320 Sport Wagon
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