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Old 11-25-2020, 08:57 PM
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What is a Mercedes-Benz Crankshaft Sensor?

What is this and what function does it perform?


https://www.pelicanparts.com/More_Info/0011538428MBZ.htm?pn=001-153-84-28-MBZ&bt=Y&fs=0&SVSVSI=3305

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Old 11-25-2020, 09:30 PM
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Tachometer pick-up.
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Old 11-25-2020, 09:46 PM
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on later models, it is one of the many things that cause a NO-GO condition on the engine if it fails...
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The OM 642/722.9 powered family
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)
2008 ML320 CDI (Older son’s DD)
2008 E320 Bluetec (Younger son's DD)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech
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Old 11-25-2020, 11:38 PM
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It is an inductive pickup which counts the teeth on the flywheel. Used for idle speed control and tachometer on some models.
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Old 11-26-2020, 09:08 AM
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Expanding on what I started to get into earlier before I got distracted:

616/617 the pickup is used for tach display (if equipped) and EGR control (starting in the early 80s). Engine does not need the signal to run.

603 the pickup goes to the EDS which uses the signal for idle control and tach display. Also fed to the KLIMA relay which is the permissive for the A/C compressor (they compare a tach signal in the compressor with the engine RPM to de-energize the compressor clutch if the compressor seizes).

606 in the 124 probably similar to the 603

606 in the 210 the sensor goes to the engine computer. I have first hand experience that if the sensor fails it will shut the engine down. Not sure why, this is still a prechamber engine with a mechanical injection pump, so it does not rely on the computer knowing the crank position to know when to fire.

648/642/651 the sensor goes to the engine computer and is an integral part of the control regime for the engine so it is necessary that it is functional. These also have a cam position sensor that likewise will block the engine from firing if it fails.
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The OM 642/722.9 powered family
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)
2008 ML320 CDI (Older son’s DD)
2008 E320 Bluetec (Younger son's DD)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech
----------
gone but living on
1983 240D (body to greazzer, engine to t walgamuth)
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  #6  
Old 11-26-2020, 09:10 AM
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Buy the Hella sensor's better than bosch
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Old 11-27-2020, 04:55 PM
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It isn't needed on a 1984 or 85 300D since it simply terminates at a passive "diagnostic port" on the inner fender. That would only be used by a dealer mechanic who has a special sensor to connect there. In earlier years, there was an electronic "tachometer amplifier" plugged into that port. In 1984-85, there is another pickup on the transmission bellhousing which is used for the tachometer input. It routes thru the EGR box (behind passenger kick-panel). I don't know if the EGR box actually uses the signal, or that is just a wiring convenience. I know that you can remove the EGR box and just jumper the pins to send that signal on to the dash tachometer display. I did that when the EGR box stopped working because the OVP relay (above it) failed and I figured easier to rip all that out since the underhood EGR mess is gone anyway (impossible to maintain that stuff w/ no manuals or parts available).

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