Magic Tach fix
 

Ok this is going to get at me.

Today while at another MB owners house we were fooling around and we noticed that the only tach to work on the 3 of us cars who was there was the one that had nothing in the cap. It was completely empty. You could take it off and the tach worked just fine:confused::eek:

I've done the fix to mine twice and it bounces all over the place and Kents didn't even work after the fix. So it was too hot and I was sweating like a pig and didn't feel like draping over a hot engine but what the heck. Whatever Magic trick the previous owner of his car did I want to do it as well.

Maybe John will pipe in here soon.

Could it have been an '85 model? Nothing is in the tach amp location on the 85's but an empty receptacle.....

'84's too, think they take their reading from the transmission.

Yes it is an 85.

That is strange. The plug on top of course was empty and it was very very short so you could tell it was engineered that way. But the repceptical (female portion) was still wired and contained the slots in the correct positions for the pins.

So is it down in the tranny? If I remember correct the 115 bodies were the same way....or was that just the speedo I can't remember now...Gosh darn my memory is fading fast :idea: :rolleyes4

I'm not sure if its true, but it made sense to me.

I was told that the wires (pins 2&6?), in the 85 and on cars without a tach (my 84 euro 300TD), were there for diagnostic purposes at the factory. i.e. you could plug into them and get info from the rpm sensor.

You had the magic fix half right. You remove the cap, then remove the contents from it. But after you get stuff out of the cap, you throw a fat o-ring or folded piece of paper in there, put the insides back in, then screw the reassembled top back down onto its base.

Worked for me.

There doesn't appear to be a magic fix for the 85's. Mine has never worked, and I've pretty much replaced everything.
The rpm sensor is mounted to the top of the tranny bell housing. The EGR "computer" black box thing is in the front passenger side kick panel. Overload protection relay behind and to the right of glove box.
My plug into the EGR black box was very corroded, and I fear a pin tip may have broken off when I removed my first black box. I have given up for now......:(
Maybe '84 Cali models also had this setup, but I don't think the Fed's did.