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1914 Mercedes 28/95 hp, 83' 300SD, 93' S420, (three) 94' S420's, 95' S500 & 96' S600
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Would anyone have personal knowledge on the procedures to replace a M104.990 engine camshaft position sensor?

Specifically, if just replacing the sensor, does it require resetting the air gap w/ the camshaft (which requires taking off the valve cover I believe?

Also, does the new camshaft position sensor have to be aligned w/ a particular setting with the camshaft when installing, or will replacing and using the factory supplied shim on the engine already be sufficient (provided the replacement sensor is exactly the same as the one being replaced)?

The camshaft position sensor has 2 5mm hex bolts holding it on the left front top of the engine, and is simply a magnetic sensor.

Actually Robert has his own way of completing this effort... preferring to utilize O-scope and monitor the two sine waves created by the CPS (wire wound on core) passing in close proximity to the (2) two magnets on the intake cam gear (as the magnet field of each magnet crossing the wire wound coil head... inducing a small A/C potential due to the magnet flux, etc). Synchronization takes place during start-up to about 600 RPM.

Just curious, how you determined the existing Position Sensor was defective.
Was it damaged... head, etc... if so, definitely pull the Valve Cover and visual!

Another method:
Use a muti-meter... Ohms scale... continuity test of the coil winding.
This is a great generic test as well! Easy, fast and inexpensive, as test of coil!

Damage to the original CPS (head impact or edge cut, etc.... or you suspect an issue with magnet(s) or just nosey and want to open her up... LOL (sounds like us, huh)... pull the cover and visual actual placement/install with original shim and new o-ring.
Not necessary unless you suspect an issue!

If you replace the shim... please ensure to reinstall the SAME size of shim!

Otherwise, remove the CPS, paying attention to remove the original shim and o-ring. Reinstall the shim on the new CPS... carefully visual the location of the unit to be reinstalled and ensure it is free of any obstructions. Simply reinstall the new CPS with shim and O-ring. Carefully tighten the bolts... do not over-tighten.

If you removed the valve cover, hand rotate the engine and view the magnet(s) and new CPS head... also, ensure Magnet(s) are secure.

Good luck with your task!

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