Camshaft Position Sensor Installation

[dbmoylan]

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!

 

[jamesmc]

I'm about to carry out this job on my 111.957 engine. (CLK 230K). So a wee bump on this to highlight the OP to those that are knowable on this may be in order

All advice gratefully received.

 

[type49]

May be wrong here but from memory it's position is just between the thermostat housing & the cylinder head, held in place by one bolt. There is no need to remove anything else. Make sure O ring is present on new one. Remove old one, fit new - job done. No setting up at all. Should take 5 minutes max. Very unusual for these to fail though......

 

[Alex Crow]

yes, i would be inclined to just use the existing shim, having checked the offset with verniers. and it cannot be located wrongly as it is a snug fit in the aperture. i suspect that the air gap ought to be checked, but would be amazed to find the new sensor varied much from the old, dimensionally speaking.

 

[jamesmc]

Thanks for the input. I'll measure the old sensor length versus the new before installation to make sure they are the same. I suspect the shim is there to take up variations in tolerances from factory engine assembly rather than differing camshaft position sensor lengths. So assuming the sensors match the existing shim should be OK to run with... unless anyone is totally against that idea.

On Star it storing errors each time I start the engine..... Clear the error, restart, same error right after restart.
So, in this case, repair by replacement is based on the Star results I'm getting.

 

[type49]

On Star it storing errors each time I start the engine..... Clear the error, restart, same error right after restart.
So, in this case, repair by replacement is based on the Star results I'm getting.

This is quite normal with older cam & crank sensors. The ecu will only recieve a signal when engine is turning. Switch engine off, ignition back on & you get a stored fault (not current fault). Each time you clear fault, star asks to turn off ignition, ecu loses sensor feed again & the whole cycle is repeated. There are various patches on Star which stop this but you may not have them. If the fault is only ever "stored" then check you readings in "actual values" with the engine running. Like I said before, I'd be surprized if the sensor has failed, as this is very rare

 

[Alex Crow]

as above, i have never known a cam sensor fail on a 111 engine. best test would be to get a simple scope of the signal and compare to a known good one, but just checking resistance and then acv at cranking speed should be enough.

 

[jamesmc]

Sorry should have been clearer. In the past I have run the engine a few times with star hooked up to read actual values. The fault I have appears related to the Supercharger cutting out intermittently when the engine has warmed up (circa 85 deg C). Each time the supercharger cuts out the Cam Sensor adds another fault to Star. Once I cleared the faults, started the engine, allowed it to warm up with the supercharger working as it should during the warm up phase. With the engine is at running temp the supercharger starts to cut in and out intermittently when it should be be running full time.
During one session I counted each time the supercharger failed. After the count of 12 I stopped the engine and checked stored faults on star. The only faults stored are under camshaft sensor. The stored faults matched supercharger faults I counted. Star is racking up faults under Camshaft sensor but no faults anywhere else during testing. Hence my thoughts on replacing the very sensor that star is showing as faulty. With the absence of any other faults showing up I am tending to go with what Star is saying.

I appreciate the idea of scoping the old verses a new one but I am in the Algarve, Portugal. I have no scope, there are not MB Indies down here and the MB dealers are about as helpful as a hole in the head down here. The Star system I have says the sensor is throwing up faults. The cost is not prohibitive so I will swap out the supposed faulty unit and see what the end result is.

 

[Alex Crow]

okey dokey skip, all sounds perfectly reasonabe. do let us know how you get on.

 

[jamesmc]

Update on Camshaft 'Hall effect' sensor replacement - I completed this job last weekend.

On removal of the camshaft sensor I noted that there was no spacer. I checked the new one against the old and they were identical in internal length.

Once the new sensor was installed (with new 'O' rings seal - supplied with new sensor) I clear all recorded faults using the Star diagnostics system and started the car a few times... no faults recorded by Star during any of the start-ups nor when running.

Now for the news I really wanted to divulge
It turns out that the camshaft sensor definitely was at fault (also according to Star) and it transpires that as it was logging faults the supercharger clutch would disengage.

Having fitted the new sensor and run the car for a few trips I can report that the supercharger now works as it should and no more faults are being logged by the ECU (as far as the camshaft sensor goes).

So...

If the supercharger on your CLK (or other similar engined MB) is dropping out and you have carried out all other obvious checks ..... have the camshaft sensor checked on Star. If it's logging faults then that will be the likely cause.

 

[type49]

So...

If the supercharger on your CLK (or other similar engined MB) is dropping out and you have carried out all other obvious checks ..... have the camshaft sensor checked on Star. If it's logging faults then that will be the likely cause.

New one on me but thanks for the info

 

[Alex Crow]

thanks james, sadly i suspect this will be a 'one off'. glad you got it fixed though, must feel nice to have sorted it out logically rather than by the popular guess work many rely on

 

[jamesmc]

Hi Alex

It wasn't until too long ago that I was able to rely on Mechanical ability alone. Sadly those days have now passed. Some say it may be progress, others a retrograde step.

I have an MB, therefore Star is a tool not to be overlooked. Yes, I am pleased that it pointed to a problem and I was able to solve it using it's indicators.