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84 230CE & 84 300DT
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Discussion Starter #1
I have an '85 300D turbo an it is a California model. My tachometer doesn't work and I was wondering if anyone had any tips about trying to find the component that was the cause of the problem. I just wanted to re-list my topic. I got many good responses previously but unfortunately none of them applied to my California model Benz. There are many differences because of the emission system. Anyone out there that has one of these that may have had the problem please let me know what was done to fix it. I don't want to take it to a mechanic if it's something that I can fix on my own. The CD manual was of no help at all. Maybe I won't pay attention to it as much if I get it working again.
 

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83 300TD/97 E320/98 SL500
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I get the same problem

as well- an intermittent tach that works if I hit a bump in the road correctly, and stop if I hit a bump correctly again (CA car too, 300TD). Someone had mentioned here once that there was a tach sender in the engine compartment on the driver side fender, but I was never able to ID it. I have only the Haynes manual, and from what I can decipher from the wiring diagram, it looks like the tach is electronic and not mechanical (anyone know if this is true?)

Sorry, just me ranting, not much help...
 

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84 230CE & 84 300DT
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Discussion Starter #3
The Haynes manual will be of no help for you for this problem. Unfortunately our tachs are...

The Haynes manual will be of no help for you for this problem. Unfortunately our tachs are electronic. It sounds like you have a loose connection somewhere. The sender everyone mentions does not apply to our cars. There is another sensor at the rear of the engine on the driver's side that you could check. This one is easier to get at then the connection on the tach. You have to pull the whole cluster out to get at the tach.
 

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90 300 SE ,85 300 GD
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1985 300 TD Wagon

My '85 wagon has the sending unit on the driver's side front fender just ahead of the front wheel. This is a screw-on cap with a black strap attached to the base. I thought the sedan was the same.
 

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1983 300Dturbodiesel
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297 Posts
the CA model doesnt have that, in the same place at least (the sender)

maby its just lo...


the CA model doesnt have that, in the same place at least (the sender)

maby its just located somewhere else?
 

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83 300TD/97 E320/98 SL500
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Strange, I see it on mine...

Purchased new in CA, so I'm assuming it's a CA model? The round screw on cap sender is on the driver side fender. I took it out yesterday to take a look (broke off the #%^&@# brittle plastic tether)- the circuitry inside is encased in a ton of adhesive...

Oh well, the tach worked less sporadic this morning.
 

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85 300d turbo
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California tach trouble

California models built in 85 have an emissions package that does not use the original tach amplifier system. To cure the troubled tach, pull out the glove box (by removing the pins)- look down and right with a flashlight and you will discover mounted to the passenger side firewall a US style fuse - I think red- change the fuse and most likely it will cure the tach trouble.
It worked on my 85 300dt with the california emissions. Took only 15 minutes. Good luck!
[:)]
 

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84 230CE & 84 300DT
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Discussion Starter #8
Thanks for the "secret"! I would have never known about this fuse since no manual that I c...

Thanks for the "secret"! I would have never known about this fuse since no manual that I checked even mentions this fuse. I will try this as soon as I log off.
 

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84 230CE & 84 300DT
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Discussion Starter #9
California tach trouble

That was the problem! The fuse was exactly where you said it would be, behind the glove box. I pulled out the old 10 amp fuse and it was blown. I replaced it and the tach finally works! It was an easy fix and it took no more than 15 minutes.
THANK YOU! THANK YOU! THANK YOU! THANK YOU!
[:)] [:)] [:)] [:)]
 

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Discussion Starter #10
Well this solved one problem but it brought out another. This morning I tried going to wor...

Well this solved one problem but it brought out another. This morning I tried going to work with the car and the transmission would not upshift from 1st gear. So when I got home I removed the fuse and now the car is back to "normal". I guess there was a reason for the fuse being blown in the first place. I didn't think the transmission could be electronically controlled. There appears to be a deeper problem here.
[V]
 

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85 300d turbo
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Tach trouble

Sorry to hear about your transmission trouble. As mentioned, I changed the fuse in my 85 and it cured the tach trouble with no other symptoms. The 85 has an improved transmission that has some electonic parts, but it surprises me that it hangs up in first. The fuse is part of a controller for the EGR valve tied into the tach circuit, I don't know if it is linked to the transmission.
By the way, if your 85 has a trap oxydizer in the exhaust, it is covered under an extended warranty by Benz. Someone tipped me on this one and the dealer coughed up with a new trap(although they weren't too happy to do it!!) Changing it increased mileage and reduced exhaust restriction.
Good luck with the tach/tranny trouble.
 

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Discussion Starter #12
I didn't know that it was linked to the transmission either but it appears somehow to be p...

I didn't know that it was linked to the transmission either but it appears somehow to be part of the circuit. This is something I will need to investigate further when I have more time. It doesn't matter that much to have a working tach in a diesel.
I did know about the trap oxidizer warranty and I have made an earlier post in regards to it to let other members know. Maybe your post will help get the word out as well.
You may want to start a new thread to get more people interested.
Thanks for the help.
 
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