W124 tacho stuck at 3500rpm

1986-1995 : 200TD, 200CE, E200, 260E, 300E 2.6, 300E 2.8, 300E, E320, 400E, E420, 500E, E500, 300CE, E320, 230TE, 300TE, 300D 2.5 TURBO, E300 DIESEL, 300TD, 300E 4MATIC, 300TE 4MATIC, E36 AMG

W124 tacho stuck at 3500rpm

Postby benzy53 » Wed 19 Apr, 2017 10:57 pm

While on holiday at moment and driven the car a lot of long distances I noticed when I pulled into the motel tonight
and turned the egine off that the tacho is stuck at 3500 rpm. Started the engine again, no movment. I was searching
the internet but could only find that issue with diesel engines. Any ideas or somone had the same issue.
Everything thing else works perfect.
The car in question: W124 300TE 1990 with M103 engine
And yes it is the car in the avatar.
For any help I say thank you in advance
benzy53
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Re: W124 tacho stuck at 3500rpm

Postby Tony From West Oz » Thu 20 Apr, 2017 12:43 am

That sounds like a mechanical issue with the tacho meter movement. You may need to get a replacement tacho and fit it to your gauge.
Others may have more experience with these, than I do.
Life is a journey, with problems to solve, lessons to learn, but most of all, experiences to enjoy.

'83 W123 300D 325000km (Josephine) - sold.
'84 W123 300D replaced good OM617 912 with OM617 952 and enjoyed having good acceleration for the first time since first driving a 300D in 2002 - became engine and trans donor for 300CD Turbodiesel conversion. Now parted out.
'86 W124 300D sold (Wife's old car - sold )
'85 W123 300CD, 275 000km (Fatmobile) rebuilt turbodiesel from previous Fatmobile transplanted into 280CE
'99 W202 C250 Turbodiesel (my darling Wife's car - Sold)
'98 W202 C250 Turbodiesel (my car)
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Re: W124 tacho stuck at 3500rpm

Postby T-Modell » Thu 20 Apr, 2017 3:08 am

Hi,

I agree with Tony; this might be just dirt. You have to take the cluster apart and check the needle. It should be easily "snipped" out of position and return to 0. I'd do that before buying a new one ... maybe it's the Melbourne Outback Dust :laughing6:
Regards
Thomas

P. S.: I actually have a W124 tacho here (from a dismantled cluster); it might just be something stuck in the mechanics ... here I took a photo for you:
DSCN0903.jpg
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Re: W124 tacho stuck at 3500rpm

Postby benzy53 » Thu 20 Apr, 2017 8:37 am

Thanks for the info. When I'm back home I'll pull the cluster out and have a look and let you know my findings.
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Re: W124 tacho stuck at 3500rpm

Postby benzy53 » Thu 20 Apr, 2017 10:19 pm

Guess what happends today. After driving for about 100km my tacho suddenly decided to work again.
Everything is fine now. The question still remains why did it stop. I'll pull out the cluster and have a
good look if there is something hindering the movement of the needle. Other option is maybe the
the sensor generating the signal.
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Re: W124 tacho stuck at 3500rpm

Postby Tony From West Oz » Thu 20 Apr, 2017 11:33 pm

benzy53 wrote:Guess what happends today. After driving for about 100km my tacho suddenly decided to work again.
Everything is fine now. The question still remains why did it stop. I'll pull out the cluster and have a
good look if there is something hindering the movement of the needle. Other option is maybe the
the sensor generating the signal.
benzy53

It is good that it is now working - for how long will it continue to work?
You should be able to move the tacho needle easily with the side of a toothpick pushing in the direction of rotation. When the toothpick is removed, the needle should spring back to the 0 position every time with no signs of binding.

If you have access to a signal generator for generating tones from 200 Hz to 40KHz, you should be able to simulate the sensor signal to the tachometer.
If the tacho takes signals from the distributor, the following may be of use:
With a 6 cylinder engine there will be 3 spark signals per revolution, therefore 3KHz should display 1000RPM, 15KHz should display 5000RPM.

I discounted the sensor as it would not be sending any signal to the tacho, and the tacho has no power, when the engine is turned off.
Life is a journey, with problems to solve, lessons to learn, but most of all, experiences to enjoy.

'83 W123 300D 325000km (Josephine) - sold.
'84 W123 300D replaced good OM617 912 with OM617 952 and enjoyed having good acceleration for the first time since first driving a 300D in 2002 - became engine and trans donor for 300CD Turbodiesel conversion. Now parted out.
'86 W124 300D sold (Wife's old car - sold )
'85 W123 300CD, 275 000km (Fatmobile) rebuilt turbodiesel from previous Fatmobile transplanted into 280CE
'99 W202 C250 Turbodiesel (my darling Wife's car - Sold)
'98 W202 C250 Turbodiesel (my car)
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Re: W124 tacho stuck at 3500rpm

Postby MercMad West Australian » Fri 21 Apr, 2017 9:36 am

What sensor?

on the petrols you only have the square wave rpm output from the ezl for things such as the fuel pump relay and also the coil negative switching terminal - i cant remember which one the tach uses. The front tdc sensor only goes to the diagnostic stocket and the rear crank sensor goes only to the ezl.

highly unlikely to be electrical in my opinion as its all killed with key off.
1990 300E-24
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Re: W124 tacho stuck at 3500rpm

Postby benzy53 » Mon 24 Apr, 2017 10:25 pm

Thanks for all your in puts. I'm back home now and the needle works perfect. It
didn't happen again. I'll leave the instrument cluster in the dash for the moment
and wait if it shows up again.
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