Hello,

I recently replaced/modified the blower-motors/heating system on a Japanese import 300TD. After reinstalling the dash including instrument panel, the tach does not work. It did work before.

I have a wiring diagram that shows there is a constant power wire and a signal wire coming from the fuel pump relay. There seems to be no signal from the relay wire. Ive traced the wire back to the fuse/relay box. It seems that it does not go into the box, but a junction plug and then off into an engine bay wiring harness from there. Does any body know where the fuel pump relay is? I also have a 93 TE parts car. Does any one know if a gasser relay is the same?

An additional piece of information that may be useful to solving this puzzle is that I turned the engine over to see if it would start while I had the dash and heating stuff out of the car. It started and the contiued to run for several seconds when I turned the key off. Could this have messed up the fuel relay?

Thanks,
Jay

You might be able to find the answer to your problem by looking through the Russian EPC over on...

EverythingBenz - Mercedes-Benz Forum and Web Search Using Google

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

The tach section of the gauge cluster has a 3-pin plastic connector and a single wire spade connector. Are you sure you reconnected both? Does the clock work? Do cruise control and AC work?

You might be looking at an inappropriate wiring diagram. An 89 TD doesn't have a fuel pump relay since it has a mechanical fuel pump. The tach signal comes from the ring gear sensor behind the oil pump and gets to the tach through the Klima relay and EDS module.

Sixto
87 300D

Thanks for the replies,

I didn't realize anyone replied because I didn't receive an email notification (in future, I'll check back sooner)

Sixto,

Thanks for the clarification about the tach source. The wires are reconnected properly to the gauge cluster. There is power to the tach power wire, but there seems to be no signal on the tach signal wire. The diagram I have is from a Haynes manual and seems pretty generic...the pump relay (inferring an electric pump) did not make sense to me. I know the injector pump is mechanical, but this diargram is was what I had to go on.

I don't know if the A/C is working as I have not recharged the system yet. There is no cruise. Is there something common to the A/C and Tach? All of the fuses seem fine. Do you know what I need to do to problem-solve the signal from the switch through the Klima relay and EDS to the tach?

Thanks,
Jay

I am back trying to sort out my tach failure. I am in Canada and my car is a '89 300TD left-hand drive imported from Japan.

I cannot find the KLIMA relay. The pictures I have seen of it have KLIMA on the side of it.

On the passenger side of my car behind the battery is the ELR, EDS, kickdown, and another relay (part no. 201 540 32 45) with a 10 A fuse in the top of it. On the driver side are 3 other relays, none say KLIMA.

I have also found a wiring diagram that looks like it shows the signal starting with "X29/4" (which I cannot find a continuation for elsewhere) splitting to "N39 EDS control unit" and "N6 A/C contrl unit". At "N6 A/C contrl unit" the wire appears to split off to the tach as well.

Can anyone tell me how to trace this signal to see where it functions and where it stops?

So far I have:
-cleaned the contacts for the ELR, EDS, and other relay (part no. 201 540 32 45) including the 10 A fuse contacts,
-checked the condition of the starter ring gear speed sensor and cleaned some gunk off the tip. The overall outside condition of the sensor and its wire look good,
- and I attempted to check a signal from the sensor with a grounded 12v test light at its plug. When I touched the light to the brown wire nothing happened. When I touched the test light to the white wire the light did not light up, but the idle became very rough whenever the testlight made contact.

I would be grateful for any information to help me proceed.

Jay

Klima:
I have discovered the 3rd relay on the passenger side is the overvoltage protection relay. I have tested it as per the instruction posted in another post and it seems fine. Some posts/diagrams say the Klima is on the right side and some say it is on the left side of the car and everything I've read indicates that it must be there....but I cannot find it with the other relays in my car.

Does anyone have any other ideas?

ring gear sensor:
Does anyone know how to test the ring gear sensor? I assume it is just a magnetic pick up like would be on an electric guitar, but I don't know how to test it.

Tach in more general terms:
My tach stopped suddenly after I ran the engine momentarily with the dash and climate system dismantled. The engine did not shut off right away and I wonder if I caused some damage at that time that has stopped the tach.

Other current issues that seem to be related are: the engine idles rough, but only sometimes, the car has no cruise control, and there is no refrigerent in the A/C so I do not know if it is working.

Lastly:
The last wiring diagrams I looked at showed the wire that I expect comes from the ring gear sensor splitting before going to the EDS and A/C control unit, then again at the A/C control unit before going to the tach (it does not show the overvoltage protection relay or if the signal runs through the EDS or A/C CU before going to the tach)
I would be grateful for any advice/information that anyone could offer that could help me to problem solve this signal path.

Thanks,
Jay

Sorry I can't help you with any of the other stuff - but google came up with this

http://www.wellsve.com/sft503/Counterpoint3_1.pdf

very nice PDF (I've even saved a copy for myself!)

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

Thanks for trying to help Army,

Are you sure the sensor is a Hall type? I would expect it to send a square wave "on/off" signal counting the teeth on the ring gear; however, I don't think it has a peice of metal moving between 2 magnets.

I tried your idea of a google search though (thanks for the idea) and found a Peach Parts thread by Oldwolf that had a link to testing engine speed signal that was helpful. My reing gear senso is supposed to have between 0.2 and 2.5 kohms of resistance and mine has 9.9...So, I'll start by replacing this and hopefully it solves the problem.

Thanks again for the help,
Jay

As far as I have been able to determine, the tach, electronic speedo and anti-lock sensors are all VR (variable reluctor) sensors.

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