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1993 Mercedes-Benz 300SE & 1998 Mercedes-Benz C230
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Discussion Starter · #1 ·
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.

Thanks!
 

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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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284 Posts
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.

Thanks!
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!

Dietrich
 

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1993 Mercedes-Benz 300SE & 1998 Mercedes-Benz C230
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258 Posts
Discussion Starter · #3 · (Edited)
Dietrich, thank you for your post. I am looking at changing because I've addressed almost everything else in the LH system that feeds my computer w/ info. I am trying to stabilize a condition which sometimes I have good acceleration & other times not. I noticed also a slight rpm drop while in gear and stopped that occurs w/in 15 seconds, then every 30 seconds therafter.

The car is a 1993 300SE/W140 chassis/M104.990 engine. For the past 2-3 years I've changed many small items like the MAF, O2 sensor, spark plugs, wires, rotor & distributor, fixed vacuum leaks (i.e. purge valve recently), checked other systems for leaks, replaced oil breather hoses, replaced the electronic throttle actuator, fuel regulator, wiring harness & had injectors tested & cleaned. Recently also changed the fuel filter & 2 pumps, and confirmed 48psi fuel pressure.

I was reading that a failing camshaft position sensor could give bad readings to the computer as it helps to control fuel injection timing. The crankshaft sensors I understand are more towards a start/no start situation, which is not a problem I'm having.

I recently spent an evening trying not to damage the 2 5mm hex bolts that sure as heck did not want to loosen. Luckily I was able to do so after much effort & patience. I did not know how to test the camshaft sensor, and decided to eliminate the problem by replacing it, hoping to improve the up & down performance.

Upon looking at the sensor, it looked OK, and not broken at the measuring end. When I get my replacement part I will do as you recommend. Understand that I don't have to align anything in particular when I reinstall, just be sure to replace shim (for air gap purpose) and o-ring for oil leakage & tighten 2 mounting bolts.

I appreciate your thoughts. Thank you.
 

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1992 400 SE
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73 Posts
Dear Mr Dietrich
David here from Perth,Western Australia.
i have a 400 se , i was just wondering if you had any thoughts on a fault i have, last night the engine stopped as i rolled into my driveway , and will not run, if it is left for 15 mins or so, it will restart briefly for 1 or 2 seconds , and the exhaust smell is strange, then stops again and wont re start,. It has been rattling from the chain tensioner, which i try to prime the oil pressure when i first start by start stop several times untill the pressure needle rises in the mornings . then i start it up and the pressure is ok, the rattle stops, the only thing at 2500 rpm on the highway the needle drops to zero, and red light comes on, i was told this fault comes from the digital temp readout by the mechanic who replaced the hydraulic chain tensioner around 50,000 km ago.
i would really apreciate your thoughts , if u have any .
Regards david.
 
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