What is this sensor?
 

I have a 1980 W126 280SE Euro model that had the pulley bolts on the harmonic balancer fail. When fixing this i found what appears to be a sensor that looks like it had been smashed, perhaps when the pulleys let go. Car seems to run fine but I am thinking this has been this way since before I bought it. This likely happened a while ago because there were no clean marks like it had just been damaged. I hangs next to the power steering pump. Any ideas? The only thing I can think of is that the Tach is not working. Not sure if it is related but was thinking it may be a crank sensor of some sort. Thanks for the help.

If you are referring to the sensor that is located at around 1 o'clock or so when facing the harmonic balancer, that is the TDC transmitter for the diagnostic terminal on the driver's side fenderwell. It is not used for anything EXCEPT for diagnostic information when the car is hooked up to some shop equipment.

Satish

Silver Boat

No way Stummala!!!
This is the pick up for the tach. There should be a small round magnet on the balancer which sticks out about 1/8". There should be a sensor with a wire mounted at 1 o'clock which picks up the pulse from the magnet as it whizzes around.
On some cars, this is used as a trigger for the ignition. It tells the computer where the crank is so it can figure out when to spark, and inject. That it why it is called a "crank sensor"
TA DA!:D

Sorry buddy,

NOT in a W126 gas engine car! The tach signal is generated by the EZL/crank position sensor and NOT by the TDC transmitter on the front crankshaft.

It IS an RPM sensor but used SOLELY for the diagnostic port on the fender well.

Regards,

Satish

Satish is 100% correct. The pickup for the ignition system is near the flywheel. If its a V8 then it generates 4 pulses per revolution, a six cylinder then 3 pulses per revolution etc. The pickup on the flywheel senses the ringgear which is machined with special pickup points. The one on the harmonic balancer could not be used to fire the ignition since there is only one pulse per revolution. Think about it.

It IS an RPM sensor but used SOLELY for the diagnostic port on the fender well.

Also, it's NOT called a crank sensor as you stated. It is called the top-dead center transmitter. The crankshaft position sensor is located near the rear firewall on the side of the ringgear/flywheel where the transmission and engine mate (approximately 1 o'clock position when facing the front of the bell housing).

Satish

Ok so it is only for diagnostics then, good to know. I thought the car might have been in some sort of "limp home" mode or something. I have no warnings to indicate this. So since it seems to be running ok I will assume it is. I guess I will start tracing the tach problem after I get the clutch replaced.

Well of course, ...I was just kidding-just to get some dialog started!, ...yeah that's it! just stirring it up a little, yeah...

Hey, I took a shot.

Actually there is one of these things on my 80 240D, which apparently has an 82 engine in it.
Is this for a tach? or the afore mentioned diagnostic thingy?

In the W123 and W126 diesel cars, it is for the tach on the dash.

Satish

Well, since we got a dialog going, I might as well stir it up. You are all wrong (sort of). The tach works off a prepared signal made in the ignition controller. There are no rpm or cylinder ID sensors on the crank for engine performance (whoever said it was a test sensor was right).

The ignition is phased by the pulse generator built into the base of the distributor on all M110 distributors after they got rid of points in 1977.

Soooo, Are me and Satish correct?

On the 123 deisels, it is the tach? Which is what I think it is...

Sorry Ed, you're still wrong :)

It is what I said, it is for diagnostic purposes on the X11 diagnostic connector ONLY (on the driver's fenderwell). The tach signal for the instrument cluster is generated in the ignition box and not from the TDC transmitter as you've stated.

Satish

BUT....for the W123 diesels, you are correct, it IS the tach signal for the cluster. However, the original poster stated he had a gas engine M110 2.8L motor.

Satish

Gotta love this forum......

Boy howdy!