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  #1  
Old 12-03-2008, 04:59 PM
BioDieseLandon's Avatar
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617.952 Tachometer

Does anyone know where exactly the wire for the tachometer runs? i am having a strange problem (it might be related to coolant spraying out in my engine compartment from a leaking thermostat housing). since this happened my ABS light comes on and my tach works, but if i hit any bumps in the road the light goes off and the tach quits working. it sounds like it would be a loose connection because it constantly goes on and off but i just dont know where to look. not to mention i dont know why the tach and abs would have any sort of relation. thanks.
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  #2  
Old 12-03-2008, 05:22 PM
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The tach in an '85 is connected to the EGR computer. I don't know where it is in an SD. The tach signal comes from a sensor at the rear of the engine. The common thread may be the overvoltage protection (OVP) relay or its fuse. The OVP relay in an SD is in a box near the fusebox, according to the 1985 "Introduction into service" FSM. In addition to possible corroded contacts of the relay and its built-in fuse, the little circuit board in the OVP can develop cold solder joints over the decades. I would check the OVP first.

Doesn't the SD have a 617.951 engine?

Jeremy
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Our all-biodiesel family
1995 E300D (W124) . .239,000 miles My car
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  #3  
Old 12-03-2008, 09:10 PM
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Quote:
Originally Posted by Jeremy5848 View Post
The tach in an '85 is connected to the EGR computer.
I have the electrical schematic for the SD if anyone wants it. It's too big to post, so PM with an email address to get it.
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  #4  
Old 12-05-2008, 07:57 PM
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The problem seems to be a loose conection or something minor because it works on and off in short amounts of time and when i hit bumps.
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  • 1993 Mercedes-Benz 400E *146,000 Miles*
  • 1985 Mercedes-Benz 300SD Turbo Diesel Biodiesel *SOLD @ 346,000 Miles*
  • 1984 Mercedes-Benz 300D Turbo Diesel Biodiesel *SOLD @ 284,000 Miles*
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  #5  
Old 12-05-2008, 08:15 PM
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ok so from what i have gathered my OVP relay must be bad because the fuse on top of it is intact. can you actually take the cube apart and fix the solder joints?
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  • 1993 Mercedes-Benz 400E *146,000 Miles*
  • 1985 Mercedes-Benz 300SD Turbo Diesel Biodiesel *SOLD @ 346,000 Miles*
  • 1984 Mercedes-Benz 300D Turbo Diesel Biodiesel *SOLD @ 284,000 Miles*
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  #6  
Old 12-05-2008, 09:52 PM
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Some folks have reported success, yes, but I have no experience with the procedure.
__________________

"Buster" in the '95

Our all-biodiesel family
1995 E300D (W124) . .239,000 miles My car
1996 E300D (W210) . .313,000 miles Wife's car
Santa Rosa population 170,685 (2012)
Total. . . . . . . . . . . . 722,685
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970
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