Why no tach amp in 85 300d?
 

while retrofitting a tach to my 82 240d, I noticed that my 85 300d does not have a tach amp under the hood. What drives the tach? Is the amplifier in the tach in the 85?

The EGR computer drives the tachometer which picks up its signal from the flywheel sensor.

good info, forced- any ideas on failure causes in this year?? I shoved ciggarette butts somewhere- but it didnt work......

I don't think it can be the EGR computer because the '84 doesn't have a tach amp and it doesn't have an EGR computer.

I believe it does, especially since a tach can be added to the later 240D using the EGR computer.

Where is the EGR computer on the '84??

Should be in the passenger kick panel.

Does it have a different name or function? It doesn't have anything to do with the EGR on the '84.

Thanks, that helps my curiosity, especially since i had a hard time even finding the tach wiring in the mb wiring prints when I was putting the tach in my 240. I ended up just using all the components from a 82 300D and tracing the wires the hard way.

A very well hidden fuse located behind the glove box is a very common cause for in-op tach.

Here is a pic of the EGR computer with the passenger kick panel removed. {courtesy of TheDon}

http://i29.photobucket.com/albums/c2...GRcomputer.jpg

It does effect tach function.....

Check out this Thread.

My 84 FEDERAL model TD does not have a tach amp nor does it have an EGR computer like a California model would have. I don't know about 1985 models, but you may find you don't have an EGR controller either.

Below is a detail on how the engine speed sensor connects to the tachometer - note that there is no tach amp, and that the federal and California models are different!

http://www.peachparts.com/shopforum/...0&d=1160955694

now I am confused, does only the california version have the egr computer?

its all magic

I don't know. My only experience with a Benz of any sort is my 300TD. Look for the EGR controller - if it's not there, you simply don't have one and the tach amp has been folded into the tachometer itself.