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  #46  
Old 04-17-2012, 12:30 AM
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Where does one typically find a shielded twisted pair wire?

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  #47  
Old 04-17-2012, 11:28 AM
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Quote:
Originally Posted by mjquillici View Post
Where does one typically find a shielded twisted pair wire?
It is used in audio wiring. I used it because I had some. You can use single shielded for the pickup which will do.
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  #48  
Old 07-13-2012, 12:34 PM
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Funola (Steve),

THANK YOU for this BRILLIANT post. I followed the instructions and I NOW HAVE A TACH IN MY 240D! Hooray!

(I never understood why MB would put a tach in a 300D with automatic, but NOT in a 240D with a manual transmission, where it is needed much more).

Steve's instructions were spot-on, with the exception where he gives you an 'upside down' picture of the back of the instrument cluster and then refers to the 'upper terminal' in the text. Just look at the photo and follow it exactly and don't be confused by the text.

IMPORTANT! MB made a change between 83 and 84 with the W123 Tachometer/Clock. THe 83 and earlier has a DIFFERENT INPUT SIGNAL REQUIREMENT than the 84+

Specifically,

1983 and earlier Tachs will show 5000 rpm at ~80 Hz input.

1984 will show 4500 rpm at ~10 kHz input.

This is terribly important, because it means the 84+ will NOT work on the 240D with EGR, even though physically it looks the same.

I had a friend test a couple of tachs and I took an oscilloscope on my 1983 240D to verify everything was OK before I started this project. SO BE CAREFUL!

The only thing I would change is that next time I'm at the PNP, I will pull the connector for a W123 tach/clock, so that I can wire in something that will prevent any boneheaded mis-connection of the 12V and the tach signal.

Oh, one thing that Steve doesn't show is how he got the wires OUT of the EGR controller. I ended up using the Dremel tool to carefully cut a circular notch into the side of the EGR controller case where the PC Board is connected with screws. I then used a rubber grommet to fit in the notch and passed the shielded twisted-pair cable through the grommet. It looks great.

Everything seems to work just fine, and it of course looks totally stock! That's just too cool. Steve must be an EE to figure this out. I just never would have thought of it.

Kudos Steve on what is now my FAVORITE MOD to this car! I love it!

Sincerely,

PE

P.S. I have no way to know if my tach is actually accurate, as I have no calibrated instrument to compare it against. How do you guys do this? There is a potentiometer on the tach that presumably can be used to to calibrate it.
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  #49  
Old 07-13-2012, 02:09 PM
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PE, glad this DIY helped you get a working tach in your 240D. It was not hard to come up with this DIY. It all started by trying to repair burned out tach amps and that was easy once I stripped the potting compound off. When I saw that the 240D EGR computer used the same chip as the tach amp, finding and getting the signal out from the EGR computer and feeding it to the tach was easy also.

Thanks for pointing out the upside down pic and the incorrect text. I can't edit my post anymore (it's too old), otherwise I'd update it.

Your best bet calibrating your tach is buy a photo tach for around $12 on Ebay. It's a great tool for the price.
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  #50  
Old 07-14-2012, 02:27 AM
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I have pulled 2 of these EGR computers and the wiring harness out of 82 and 83 240D`s. pulling the dash, then carefully followed every wire to see where they all went. (these are things you do when you are retired with lots of time on your hands)

Had thoughts of using this thing for our 80 240 so I could install a tach. seems simple enough. 2 wires go to the fuse panel, one to the spedo sensor and branches off to the cruise control, a ground and the cable that runs to the crank pully on the front of the engine. Found a Tach out of a 83 300D last week. now where did I place my notes.?

Using the Tach amp on the inner fender as 90% of these cars use seems to be PITA constant problem keeping them working.

Charlie
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there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works
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  #51  
Old 07-15-2012, 04:35 AM
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Quote:
Originally Posted by charmalu View Post

Using the Tach amp on the inner fender as 90% of these cars use seems to be PITA constant problem keeping them working.

Charlie
Hi Charlie

I didn't understand your comment noted here

Sincerely

Packer
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  #52  
Old 07-16-2012, 02:39 AM
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Packer, your 240 doesn`t have a Tach Amp. some of the SD`s and 300D`s have this mounted on the L/F innder fender. It`s a little black round thing that is about 2" high.

This link a single post shows what it looks like.

OM617A Tach Amp

Your 83 does have the EGR computer black box mounted behind the Pass side kick panel.

Charlie
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there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works
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  #53  
Old 08-17-2012, 02:33 PM
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I just attempted this mod... I did everything as the OP did, and my tach doesnt work. I pulled the EGR computer back out and a circuit, connected to where the ground is soldered, burned up.

1) What would cause this?

2) Does anyone have one of these modules for sale?

Pics of the problem below (before and after)





Best,

Matt
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  #54  
Old 08-17-2012, 05:55 PM
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Matt, the only things I can suggest is verify that there are no shorts to adjacent solder joints and that you wired it to the correct points on the cluster, per the photos, not the wordings (which may be confusing).

Sorry, I do not have any parts.
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  #55  
Old 08-17-2012, 06:55 PM
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I thought only the 85 300d had the computer behind the RS kick panel--the 83 cd parts car does not have this gizmo.
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  #56  
Old 08-17-2012, 09:23 PM
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Quote:
Originally Posted by funola View Post
Matt, the only things I can suggest is verify that there are no shorts to adjacent solder joints and that you wired it to the correct points on the cluster, per the photos, not the wordings (which may be confusing).

Sorry, I do not have any parts.
Do you think the guage of wire I used (a small bit thicker than yours) could be a factor?

I was careful not to touch any of the other terminals/circuits during soldering. However, my cluster did have a problem with the left hand side fuel and coolant temp gauges immediately prior to checking the functionality of the tach. They seemed to have intermittent ground... as though the cluster was not grounding itself when installed.

Could that have any bearing on the circuit burning? I have been racking my brain all day over this since this happened and it would be great to have some accurate feedback. What would/could cause that circuit to burn?

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  #57  
Old 08-18-2012, 06:02 AM
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Quote:
Originally Posted by Terpitz View Post
Do you think the guage of wire I used (a small bit thicker than yours) could be a factor?

I was careful not to touch any of the other terminals/circuits during soldering. However, my cluster did have a problem with the left hand side fuel and coolant temp gauges immediately prior to checking the functionality of the tach. They seemed to have intermittent ground... as though the cluster was not grounding itself when installed.

Could that have any bearing on the circuit burning? I have been racking my brain all day over this since this happened and it would be great to have some accurate feedback. What would/could cause that circuit to burn?

Larger gauge wire shouldn't matter. Those wires carries the tach signal to the tach in the cluster. Maybe the problem is related to the other issues you have with the cluster? I would suggest fixing the cluster so it is 100 percent operational by itself first. Post a pic of the cluster. Maybe I can spot somthing.
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  #58  
Old 08-18-2012, 08:10 PM
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Quote:
Originally Posted by funola View Post
Larger gauge wire shouldn't matter. Those wires carries the tach signal to the tach in the cluster. Maybe the problem is related to the other issues you have with the cluster? I would suggest fixing the cluster so it is 100 percent operational by itself first. Post a pic of the cluster. Maybe I can spot somthing.
I have solved the lack of ground in the cluster... What normally grounds the W123 cluster? Is it grounded through the dash once it is in its spot (?) through the bezel opening?

I ran a ground wire (from the ground wires just behind the cluster) to the cluster rear chassis. Everything works flawlessly now.... Except for my poor tach.

I have been looking for another module but have had no luck.
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  #59  
Old 10-11-2012, 12:50 AM
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Funola,

Thank you for your crafty solution for liberating 240Ds with tachs!. I followed your instructions, even though I was not getting the AC voltage values I still connected the wiring. I am wondering what kind of signal does the counter send is there a way to detect if it is working by a Digital multi meter? I saw there is a socket around the left quarter panel. and I am curious even if the EGR box is getting any power. what would be a right way to inspect that.

Thank in advance!!

Gunay
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  #60  
Old 10-11-2012, 10:33 AM
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Quote:
Originally Posted by GNY203 View Post
Funola,

Thank you for your crafty solution for liberating 240Ds with tachs!. I followed your instructions, even though I was not getting the AC voltage values I still connected the wiring. I am wondering what kind of signal does the counter send is there a way to detect if it is working by a Digital multi meter? I saw there is a socket around the left quarter panel. and I am curious even if the EGR box is getting any power. what would be a right way to inspect that.

Thank in advance!!

Gunay
The tach is an AC signal so put the meter on the lowest (most sensitive) AC scale.

"socket around the left quarter panel." What socket? Got a pic? What year is your 240D?

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83 240D 4 spd manual- parted out then junked
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