OM617A Tach Amp - Page 7 - PeachParts Mercedes-Benz Forum

techguy512 · #91 08-19-2010, 06:00 PM

Quote:

Originally Posted by JHZR2

...but is it possible to somehow rig up an amp to run an external tach as opposed to the one in the instrument cluster?

This problem has been solved for the most part....

http://www.mbelectronicupgrades.com/Project-Aftermarket_Tach.html

What kind of readings are you getting? Consistently a few hundred RPM low across the range, or something else?

JHZR2 · #92 08-19-2010, 06:21 PM

consistently a few hundred below. I think that when the cluster needles got repainted, the tach needle didnt get put on straight... But I want to check easily... thus I was hoping to pull a signal off the tach amp through another 617 tach...

4x4_Welder · #93 08-19-2010, 09:50 PM

That's easy with some jumper wires and a spare tach. You just need to supply 12v and ground to the tach, then jumper the signal wire from the amp to the input on the tach.

newtodiesel · #94 08-19-2010, 10:31 PM

Tell us about the wiper thingy...what will it do??
Nevermind I found the website...
nice fix

http://www.mbelectronicupgrades.com/Pulse_Wiper_(old_and_new).html

JHZR2 · #95 08-20-2010, 07:35 AM

Quote:

Originally Posted by 4x4_Welder

That's easy with some jumper wires and a spare tach. You just need to supply 12v and ground to the tach, then jumper the signal wire from the amp to the input on the tach.

Understood... what is the best way to jumper that signal wire though?

MNBenz · #96 08-25-2010, 11:36 PM

I bought the MB electronics tach amp and it works great! Finally have a tach again, I definitely recommend the product.

beermc00 · #97 08-26-2010, 02:13 PM

I want everyone to know that if your car uses this style of Tach Amp, Techguy's (Bob's) replacement will probably fix your tachometer. He sent me instructions on how to do a few easy electrical tests with a multi-meter before I bought it because I was sure that my 1983 300D was going to need other parts to get the tach working again. Reason being, I attempted the trick of putting a washer shim on top of the old amp and that blew my #8 fuse and then the amp and the plug it goes into smelled like burning electrical wires...not good.

After my car passed the three preliminary tests Techguy emailed to me, I bought his part and installed it in less time than it takes me to check my oil and the tachometer now works perfectly...plus that self-test, sweep thing it does while you are waiting for the glow plugs is pretty cool.

Thanks for reading!

bricktron · #98 06-14-2011, 03:00 AM

what would it take for this kit to work on 1st gen 123s? - which of the other bits is a base '77 240d missing?
edit - it's the EGR, right?

Benzmizer · #99 07-11-2011, 10:36 AM

@techguy512: You have PM/email.

toomany MBZ · #**100** 07-11-2011, 11:32 AM

Quote:

Originally Posted by bricktron

what would it take for this kit to work on 1st gen 123s? - which of the other bits is a base '77 240d missing?
edit - it's the EGR, right?

You'll need a wiring harness and a three (I think) pronged tach, as the 240's didn't have a tach from the factory.

No, it isn't the egr.

junqueyardjim · #**101** 07-11-2011, 12:43 PM

Well I sent Bob a PM also, 2 of them really, and then after thinking about it, it could be that this is a common problem for those of us who are putting 617's into formerly 240D cars. I now have mine running and it is a real peach, but I don't have a tach. I did save most of my tach wiring from the 85, but I did not get the signal send out of the right side signal sender. So all I have right now is the 85 instrument panel with the tach installed in the car, also have the position sensor mounted at or on the bell housing to sense the flywheel turning. I really miss my tach and really hope he can help me get that instrument up and running on my 1983 which formerly had a 240D and no tach.

edge · #**102** 04-21-2012, 07:57 PM

Quote:

Originally Posted by rcounts

For those wondering about the 84 and 85 models and the tach amp, my 300 CDT (production date 01/84 - must've been one of the first one off the line that year) there is NO tach amp under the cover on the assembly mounted inside the DS fender. If you remove the cover and look at the sockets, the #3 socket (they are numbered) doesn't have the metal female pin in it.

On this style the tach gets its signal from a different sensor mounted at the BACK of the engine in the bellhousing of the transmission - just behind and below the bottom of the oil filter assembly. The sensor is held in place by an allen-head screw and it takes a 5mm allen key to remove it.

My sensor is bad and needs to be replaced. You can test it by unplugging the 2-wire cable connector at the center of the hood opening just in front of the cowl. If you follow the wire from the sensor up to the connector it is easy to find.

With the car off, connect an Ohm meter to the two make pins of the cable connector. It should measure 1.9k Ohms +/- .2k ohms (that is 1900 Ohms +/- 200 ohms). If that measures OK, then start the car and use a volt meter to measure the voltage across those same tow pins. At normal idle speed of 750-800 RPMs it shoud measure ~4V +/- .1V.

If EITHER of these measurements is outside these value ranges, it needs to be replaced. Mine measured 2024 ohms (in spec) but only a few millivolts at idle.

Can someone help me out with a part # for this tach sensor?