After having hot start start & stalling problems, the issue was traced to the "Position Sender Unit"

This resembles a small spark plug wire, but is listed as a sensor. I was told it transmits or regulates ignition firing data between the ignition control unit and the engine.

But is it an actual sensor or just a wire?

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2008 E350 4matic / Black/Anthracite

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Gone but not Forgotten:
2001 E430 4matic, 206,xxx miles, Black/Charcoal
1995 E320, 252,xxx miles, Black/Grey
1989 260E, 223,00 miles, Black/Black

So you wish to have spark. When do you wish to have spark? The story I heard was that it must occur at just the right POSITION when the fuel air mixture has been squeezed to the max by the piston coming to the top of the cylinder.

Located in the bellhousing of the 103 motor is the crankshaft position sensor and its job is to tell the ignition controller where the crankshaft is and how fast it is moving.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

And when you wish to have spark, and the sender is deteriorated and frayed, the ignition comtroller gets no feedback, and stops firing?

Thanks Steve. I was having no-start and stalling problems in the extreme heat last week, and the sender unit was in pretty bad shape. The engine would initially catch for perhaps half a second, and then shut down. I am glad it was a relatively simple fix.

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2008 E350 4matic / Black/Anthracite

------------------------------------
Gone but not Forgotten:
2001 E430 4matic, 206,xxx miles, Black/Charcoal
1995 E320, 252,xxx miles, Black/Grey
1989 260E, 223,00 miles, Black/Black

Steve,

FYI, spark does not occur when the fuel/air mixture has been squeezed to its maximum. Because of the speed of flame propagation ignition occurs some degrees before top dead center (BTDC), or so my thermodynamics teacher told me 40 years ago.

Kip,

What your thermodymanics teacher should have told you is that the optimum firing point varies according to engine speed, load, octane rating of fuel, inlet air mass flow, engine temperature and just about anything else you care to think of. So the position sensor tells the computer each time the engine passes TDC on cylinder No 1, other sensors relay the other information and the computer calculates the firing point accordingly.

I can promise you Steve knows this, he was just simplifying it for ease of explanation.

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Mick J
'08 Chrysler 300CRD (MB OM 642 engine)
'95 E220 estate
'89 230TE (R.I.P.)

Mick,
My response to Steve concerned when ignition occured and not what the position sensor indicated.

Ahh... but we were talking about position sensors and my statement was identifying "just the right position". Lots of factors contribute to where that is to achieve maximum "squeeze".

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

It's more precisely referred to it as a "TDC sensor", and it provides the EZL with a position reference for computing spark advance.

On my 2.6 it is located at the front of the engine, next to the timing pointer, and detects the TDC dowel pin on the crankshaft damper. It has a shielded cable leading to the EZL module on the fender apron.

Duke

The sensor on the front of the motor is not involved with engine management. It is there for diagnostics. It provides TDC info for an engine analyzer.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

I understand the TDC sensor simply sends TDC position information to a computer, tach, or a diagnostic plug - depending on the car.

I have installed a tach from an '82 Mercedes 300d Turbo in my '77 Mercedes 280E and have wired it exactly as per a 300d turbo Mercedes wiring diagram. I have used my existing TDC sensor, connected to an additional diagnostic plug containing a new tach amp. The result is just as if the tach amp were bad - a wandering & sometimes dead tach. I bought the new VDO tach amp on e-bay and it looks new. ?

Additionally, one of the terminals on the 300d tach amp diagnostic plug had an extra wire, not shown on the wiring diagram, so I discarded it. Did I screw up? So I am wondering if I need a new TDC sensor, or to reconnect the mystery wire.

I thank you for any input,

Stephen