PeachParts Mercedes-Benz Forum - View Single Post - Where is the RPM sensor on a W123 diesel?

pawoSD · #10 02-08-2006, 03:15 PM

Quote:

Originally Posted by dieseldiehard

No, the pickup is a coil of wire with almost no current flowing in it, it generates a weak electrical pulse when the small metal (magnetic?) tip of the projection on the crank pulley passes by.
The cable to the pick up coil is something that can break though and I've seen that happen during an engine removal or swap
Usually the failure is in the tach amp module on the fender or in the case of the '85 diesels the EGR box in the car behind the glove box.

Thats what I thought, I tried to fix my existing amp (the gauge would occassionally "go crazy") then later on it all but died. The amp messing did nothing, so I bought a brand new one, it also made no change, so I cleaned and made sure the contacts were good in the socket, nothing. So I bought a new tach-gauge pod, still nothing.....so I tested the wires that plug into the tach pod in the dash, it had 13.4 volts at idle. So the problem lies somewhere beyond that....I just have no clue what else to check. The pickup appears to be ok.....how does this system actually work....is the gauge reading a "sine wave" from the electrical supply coming into it? Mine has never so much as even quivered in the years since I messed with it.