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Old 02-20-2011, 09:39 AM   #1 (permalink)
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Tachometer not working

For some reason the tach was working intermittently right after an oil change than stopped all together. It is possible a wire or sensor was disturbed and where should i be looking... any ideas. Im not sure where to begin on this one. would it be electronic or vacuum realated?
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Old 02-20-2011, 04:13 PM   #2 (permalink)
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woops.... forgot to mention the make etc...
1987 300d turbo
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Old 02-20-2011, 04:37 PM   #3 (permalink)
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The engine was running fine when the tach was working, but when it intermittantly stopped the engine would run slightly rough, now its stuck in this mode with no tach. Its the SAME thing that happens when you turn the key back slowly while turining the eninge off. Im convinced that something disturbed when the oil was changed and or the engine bay wash pressure washed.
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Old 02-21-2011, 01:00 AM   #4 (permalink)
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I have checked numerous things and all vaccum lines are intact and working. This problem is common and it traced to the OVP relay when these symptoms exist along with ABS light and no AC. My ABS light is off and the ABS is working fine. My AC normally works however due to the extreme cold here i cant tell if it is working because the temp is below minimun AC clutch engage temp. Im thinking its the tach or rpm sensor. Anyone know where this is?
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Old 02-21-2011, 02:25 AM   #5 (permalink)
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hi
603 engine, right? tach is picked up from a crank speed sensor, just below the starter (I was lying on my back and may remember the orientation wrong..)
easy to get at from below, there was one line which looked like it might be in the way but turned out not to be a problem - 5mm Allen iirc
My 300TD also had the wire trapped and crushed between the bits of firewall and stuff due to ham fisted work by PO
Ah, this might help
http://www.benzworld.org/forums/w124...00td-tach.html

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Old 02-21-2011, 01:59 PM   #6 (permalink)
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This morning I started the car up and it took several attemps for it to fire up. Once it did the idle was still low and no tach. I drove the car to my friends shop and went right to work on the Ring Wheel Sensor, removing it i noticed that it was covered in metal particles and grease. I cleaned it with electronics part cleaner and reinstalled it, next I check all the grounds and cleaned the contacts. Started the car up and PRESTO. Idle is restored to normal and I have a working tach. Thanks for the help!
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Old 02-21-2011, 02:43 PM   #7 (permalink)
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Thumbs up

Result!
Nice one, the sensor only cost me about £20 odd, but free is a good price for any repair!
Only possible fly in the ointment is how all that grunge got there in the first place? although I guess 25 years wear and tear could be a good excuse...
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Old 10-14-2013, 04:36 AM   #8 (permalink)
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Quote:
Originally Posted by kzs983 View Post
This morning I started the car up and it took several attemps for it to fire up. Once it did the idle was still low and no tach. I drove the car to my friends shop and went right to work on the Ring Wheel Sensor, removing it i noticed that it was covered in metal particles and grease. I cleaned it with electronics part cleaner and reinstalled it, next I check all the grounds and cleaned the contacts. Started the car up and PRESTO. Idle is restored to normal and I have a working tach. Thanks for the help!
Where is this Ring Wheel Sensor located. I have a dead tachometer as well on my 260E. Thanks.
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Old 10-14-2013, 10:44 AM   #9 (permalink)
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I have a spare one that I never installed. Will ship for $40.
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Old 10-14-2013, 10:49 AM   #10 (permalink)
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A dead tach on a diesel can also be caused by a bad OVP relay.

Replace the OVP first with a new genuine MB or KAE(hler) relay.
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