Tachometer on a w124 diesel

[davdog]

How does it work ? Where is the signal fed from - anyone know ?
The Haynes manual doesn't cover it and mine is not working.
Cheers

 

[dieselman]

I'm not particularly au-fait withthis car, but I believe it uses a pickup from a hall effect sensor which is amplified by a plug in amp. situated under the diagnostic socket cover. Apparently the module connections become loose.
A common fix is to wedge it down with a cigarette butt or folded card, then srew the cover back down.

 

[davdog]

Thanks for that - I will check it out as soon as the car comes back from the garage.....

 

[Zanimat]

I'm not particularly au-fait withthis car, but I believe it uses a pickup from a hall effect sensor which is amplified by a plug in amp. situated under the diagnostic socket cover. Apparently the module connections become loose.
A common fix is to wedge it down with a cigarette butt or folded card, then srew the cover back down.

I'd like to use this signal with a non-MB cruise control but can't seem to locate the item you mention (diagnostic socket cover). Can you point me in the right direction, please? TIA

 

[Zanimat]

Did you have any luck, Davdog? I'm still looking for the diagnostic socket D'man refers to. Hope you can help.......TIA

 

[Keith]

depends how old and which engine you have

Mine's a 95 OM606 and has a sensor mounted in the rear of the engine itself but not sure where the connection goes, but mine was intermittent so I wiggled the wire and its fine for the moment!

Older ones I believe have a hall effect sensor mounted in a round black canister on the inside of the left side above the wheel arch. Thats the sort that the cigarette but fix works with I believe.

Keith

 

[Zanimat]

Thanks Keith.....don't seem to have anything like that on my '88 300D. But there's something that looks a bit like a glowplug (but isn't!) near No1 cylinder with a single wire going back thro' the bulkhead panel & disappearing under the brake servo. I'm wondering if that's the tacho lead. Suppose I could try disconnecting it & see if the tacho stops working.......

 

[pascal]

Zanimat and Dav

The tach sensor on most older diesels is on front of engine crankshaft. It takes the signal from the rotation of the crank pully. You should see it behind the pully.

Pascal

 

[Zanimat]

Thanks, Pascal - nothing of the sort on my engine, though :sad:. I tried disconnecting the lead from the item I though might be a tacho sensor, but the tacho carried on working so that's not it, either :roll:

 

[pascal]

Okay. it's not on the crank pully.

It may be taken from the altenator, as with some other diesels