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+--- Thread: Tach in a 240D (/showthread.php?tid=1073)
Tach in a 240D - CID Vicious - 01-25-2010
I've been told this is possible and I'd like to replace the useless clock in my dash with a stock tach. What parts would I need to pull from the yard?
RE: Tach in a 240D - ForcedInduction - 01-25-2010
That depends on the year.
81+ owners have it easy, the EGR computer already provides the signal, you just have to add the tachometer and two wires.
76-80 owners have to add the pickup, amp and wiring from a 617a.
Parts needed:
Tachometer with two prong plug, three will not work, and a few inches of the pigtail.
Pickup sensor, all OM61x engines have the bracket in place to mount it.
Base/amp bracket, all W123 models have predrilled holes to mount the bracket on the drivers side fender by the glowplug relay.
Amp base and a few inches of it's pigtail.
Tach amp.
16' of ~24 gauge wire.
Misc electrical butt connectors, tape.
Wiring:
Plug white pickup sensor into it's base socket.
The pigtail of the amp base will have 3 wires- Brown, green, black.
Brown is ground, attach it to any clean ground connection in the engine bay.
Black is power for the amp and tachometer. Connect it to a switched power source (there is one in the glow relay) with an inline 1amp fuse, run that wire from the amp base to the black/red stripe wire on the tach pigtail to power both the amp and tach.
Green is RPM signal output. Run that wire to the green/stripe wire of the tachometer pigtail.
Start the engine and enjoy.
Original discussion- http://www.superturbodiesel.com/std/adding-a-tachometer-t-97.html
RE: Tach in a 240D - cell - 01-25-2010
CID, here's another route:
when I put a differential pressure sensor across my primary fuel filter (see http://www.peachparts.com/shopforum/showpost.php?p=2257058&postcount=271), I noticed the pressure drop is sinusoidal, and tied to the speed of the camshaft. its regular enough that you could easily make a tach signal from it.
I've actually been thinking about making such a tach, but it would be for a non-standard gauge. What sort of interface does the standard tach gauge take? is it just voltage controlled?
RE: Tach in a 240D - CID Vicious - 01-25-2010
Is the EGR computer the one attached to the under-dash panel on the driver's side? I'm in luck! 82, baby!
So all I need to grab is a factory tach, eh?
Sweet!
RE: Tach in a 240D - CID Vicious - 01-25-2010
Both my under dash box and the one on the inner DS fender look significantly different from that.
RE: Tach in a 240D - ForcedInduction - 01-25-2010
It should be behind the passenger side floor kick panel.
RE: Tach in a 240D - Syncro_G - 01-26-2010
I just ripped out all EGR, computer and harness and so had to switch to the little amp can.
I have been exchanging email with Bob Myer (the MB electronics tech guy). He's working on a new revision of the tach amp that will have oversampling options so you can use a wider range of tachs. He has 2x and 4x already and is working on 3x so you can use a tach from a straight 6 gasser
RE: Tach in a 240D - OM616 - 01-26-2010
(01-26-2010, 01:36 AM)Syncro_G I just ripped out all EGR, computer and harness and so had to switch to the little amp can.
I have been exchanging email with Bob Myer (the MB electronics tech guy). He's working on a new revision of the tach amp that will have oversampling options so you can use a wider range of tachs. He has 2x and 4x already and is working on 3x so you can use a tach from a straight 6 gasser
Will an aftermarket (race type) tack for gas engines work with the tack amp?
RE: Tach in a 240D - Syncro_G - 01-27-2010
(01-26-2010, 04:57 PM)OM616 Will an aftermarket (race type) tack for gas engines work with the tack amp?
that's the intent.
RE: Tach in a 240D - Grassroots - 02-18-2010
Why would you need a tachometer? There are little red lines on the speedometer indicating when to shift..... ROFL! That is such a joke... just giving ya crap.
RE: Tach in a 240D - ForcedInduction - 02-18-2010
(02-18-2010, 04:25 AM)Grassroots There are little red lines on the speedometer indicating when to shift.
Those are downshift points, the upshift is a bit higher.
RE: Tach in a 240D - CID Vicious - 02-18-2010
Besides, those are only guidelines, they tell you nothing when you're trying to diagnose the motor, and if you change the diff or the tires they're skewed if not entirely worthless.
I got a better question, who needs a clock instead of a tach in a car this expensive? Jap subcompacts had tachs back then!
RE: Tach in a 240D - JB3 - 02-18-2010
(02-18-2010, 10:44 AM)CID Vicious I got a better question, who needs a clock instead of a tach in a car this expensive? Jap subcompacts had tachs back then!
What kind of question is this? Clearly its so you can make it to luncheon at the club on time, followed by a round of golf and cocktails on the sailboat! All these things are time critical!
Let the subcompact drivers worry about lesser things like engine rpm.
RE: Tach in a 240D - CID Vicious - 02-18-2010
Bah! If you can afford a Benz, I'm assuming one can afford a Timex as well!
The 300D got it right...big tach, tiny clock (perfect size to be drilled out and replaced with a boost gauge!)...
Besides, if you like getting sideways in dirt, those dots on the speedo aren't worth much...
RE: Tach in a 240D - Grassroots - 02-18-2010
well if you are driving a 240D time is irrelevant anyways so why have a clock?
RE: Tach in a 240D - Nick - 02-18-2010
They must of put that giant clock in the 240D's so you could actually watch a needle moving while you accelerate
Thanks for sharing that Forced, i used to have a piece of wood sandwiched between the hood and the tack amp to make it work, and it all got fubar'd when I rolled my car.
In my anger of my tack playing dead again, I ripped everything out and plan to wire everything up in the cabin where it should of been.
RE: Tach in a 240D - btrapr - 02-21-2010
Can someone post a pic or two of the AMP can on the fender and what else that needs to be removed from a Mercedes to get the parts needed to get a tach into both of my 240's?
thanks in advance
RE: Tach in a 240D - CID Vicious - 02-21-2010
The amp can on the fender is only on the 300D models with a tach. As stated above you'll need to modify the EGR box to gain a tach signal, and all you need beyond that is some wires and the stock tach from a 300D/DT/CD.
If yours is a pre EGR model you'll have to retrofit the parts. The tach amp is a 1" diameter, 1.5" tall 'knob' on the driver's fender in the engine compartment.
RE: Tach in a 240D - willbhere4u - 02-21-2010
Here is a pic of the tack amp but not the base it sits in. It sits upright on top of the LH/drivers inner fender
RE: Tach in a 240D - Syncro_G - 02-22-2010
Here's some instructions from Bob Myers - this shows the socket and what the pins mean.
The gas cars had a test socket that was essentially the same but missing the tach signal pin. So you could grab one of those too.
BTW, his current tach amp works great when used with the stock MB diesel tach. We're still working out how to make it work with a gas car tach. pulse shape and amplitude are quite different (as are the number of pulses per rev).
