Here are 2 pictures of the connector that leads to sensor by the crank shaft. I was wondering if there is a way to detect the signal (current, voltage, resistance, etc.) if it actually picks up the rotation. My suspicion is my EGR unit is not getting any power. I did not have a chance to check today but I will first thing next week. I also attached a schematics I found for EGR. Basing the schematics I was planning to check if there is any sort of voltage between the leads of 2 and 3, would this be correct approach? If there is no power I will need to follow the wiring to find the disconnection. I saw one wire cut around that area. I hope this is not confusing and I could explain my situation.

And my 240D is 1982 (Auto)

Thanks

Attached Files

	TDC Cable Socket.pdf (276.0 KB, 231 views)
	EGR Schematics.pdf (138.5 KB, 228 views)

Ahhh that connector! Use an ohmmeter to check the sensor, if around 80 ohms it's good. Clean the connector contacts and make sure sensor gap per FSM.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Thanks for the info. Every weekend I drive 600 miles round trip. I recently installed a 2.88 ratio differential and While I was swapping to matching speedometer I saw your thread and I wanted to add the tach as well. Today though on the way back during my drive, at the very beginning I saw tach working very briefly. I was shocked!! but it did not last long. From that experience I am thinking the sensor works fine but there is a connection issue somewhere. Also it did not seem very responsive while idling. It was a little above 500RPM mark most of the time. I could not see any change when I switched to neutral, should not it be running slightly higher RPM in neutral compared to be at drive while waiting for the traffic lights? I also saw a potentiometer at one side of the tach when installing, is that for calibrating needle's location or for something else. And my final question: I saw you used a coaxial cable, was this intentional? does that affect the quality of the signal? I just used 2 single strand wire. Apologies for so many questions but you seemed to know what you are doing and I just wanted to share my observation. Are my assumptions correct?

Thanks again!!

If the tach worked briefly it could be:

1. intermittent electrical contacts. clean them!

2. gap on pickup too large. set gap!

3. tach needle sticking. take the tach out and turn needle back and forth by hand a bunch of times!

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Thanks again for the answers. I did check the connections today and after that I checked the pickup I played with it a little but it was very messy there and hard to reach. I started to check for continuity and all that. I actually could tell the pickup was working by measuring the voltage between pins 2 and 4 this is the signal before it is amplified. The AC voltage reading was around 0.28mA at idle and it would reach up to 0.65mA when revving around 3000RPM ish. I was just getting desparate and thinking that something is wrong with the board which it was. While I was playing I saw the tachometer needle come up and I narrowed it down to an area circled in the picture. It seems like 1 or more of these 3 components seems to have a connection issue. I moved them around and flexed the board a little and could make it work for a short time and captured an image during test drive with tach working. I heard crunchy noises when I was moving these components. I will investigate more later, see if I can buy these components or they are too old to buy. Not even sure what they are. Thanks again for this very straight forward DIY. I will figure the rest out and stop clogging the forum with my obstacles

Attached Files

Malfunction area and Tach in action.pdf (286.3 KB, 221 views)

I did this job on my '82. It works like a charm!
Many thanks to Funola for sharing his knowledge!

Funola's mod is great and I've performed it on my 83 240D and several other cars. I've had the problem you describe more than once.

The most common problem I find with these EGR/Tach units is bad solder joints. In all likelihood you just need to resolder some bad joints on the board. See the attached image for an example of a bad solder joint.

The next most common problem is bad capacitors. The large can in your picture marked 220/16 is a 220uf (microfarad) 16 volt (dc) radial electrolytic capacitor. These are easy to find from websites like Digikey and Mouser. You can also likely find them at Radio Shack. Be advised they are polarized so take note of polarity. The positive terminal on your part is marked "+" A new replacement capacitor will be marked with a negative stripe. Take a picture beforehand. Higher voltage is fine but stick to the same value in microfarads. If the new part is electrically identical to the old it will be physically smaller in nearly every case. Not a problem - just progress.

At this point I recap everything. Clocks are notorious for failure and delay wiper relays are known to fail as well. I have a Becker Europa on the bench with this problem. When one fails all are suspect. The parts are cheap and easy to install if you can solder.

In any case since yours works you likely only need resoldering but I would recap while you're in there. Best of luck.

Attached Thumbnails

 

__________________
1969 220D 5 Speed (OM616)
1983 240D 4 Speed
1985 300D Auto 376K
1985 300D Auto 275K

Excellent! Did the 82 come with the EGR controller or did you have to source one from an 83?

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

It was right there where you said it would be. Same numbers.
My temp/pressure/fuel-level gauge was laid out slightly differently than your picture but the voltage-tap still worked.
Thanks again!

Subscribed .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

This post is awesome - I really want to trade out the clock on my 83 240 for a tach. I've been looking at your post and it looks doable.

The questions I have are....

What year / model did your Tach come out of? I've been looking on ebay to pick up a tach and there seems to be some differences in the 81 - 85 300 tachs. Some seem to have two prong connector on the back and others seem to have three. What year / specific model vehicle did your donor tach come from? and Will any 300 td tach work?

Does the clock on your new set up work? Which wires in the diagram are related to the clock?

Thank you for the awesome post!

Tach came from my 83 300D turbo which I had at the same time as the 83 240D. I think a tach from any W123 300D turbo model year except 85 will work. The clock worked (car long gone). It is powered by the same single spade connector that powered the 240D clock. You'll find a single spade on the back of the clock of the new 300D turbo tach/clock combo.

Note: you must have the exact EGR controller pictured.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Now that I own an 85 300D and looking at the pics in this post from 2007, I recognize the connector of Pizzachef's "device" from his 85 300TD Euro has the same type of connector as the EGR controller on my 85 300D US. However, the EGR controller on my 85 has a black plastic casing that is bigger, more square in shape than the rectangular aluminum case pictured.

Does 85 300TD Euro have a tach?

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Thanks. Any chance of getting a rpm reading for say 60 and 70 mph? Just need a reference. You're the man

You did the mod and have the tach working? I do not have the info you are looking for. Buy a photo tach (around $10 on Ebay) to calibrate it.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked