E L R ???

[Zanimat]

There is a box of Bosch electronics mounted behind the battery in my W124 300D, marked "ELR Diesel 6 Zylinder". Can somebody please explain its purpose - and could it be to blame for the intermittent failure of my tacho?

Thanks, Malcolm.

 

[Bolide]

If it's an E300 Diesel and not a 300TD then it'll probably be the idle stabilisation module which I believe is electronic on the Multivalve engine

These cars also have a Cat and a Lambda sensor. Maybe that's tied into it too - and maybe the EGR system as well

I think realistically the only way you'll be able to fault-find an intermittently non-working tacho is to swop parts with a known-good car

Nick Froome
www.w124.co.uk

 

[Zanimat]

Thanks, Nick; my car's a 1988 model, non-turbo diesel & as far as I know it's only 12 valve. I've noticed that the idle speed has dropped, so maybe I'm in the right area.
The main difficulty I'm having is locating the tacho circuit components - and I don't have a circuit diagram which even shows them! Any idea where the sensor is located? That would be a start! Cheers, Malcolm

 

[Bolide]

1988 car has no (engine) electronics. I'd think the tacho signal is taken off using a speed sender (part #451) reading the teeth of the starter ring gear:

http://www.detali.ru/cat/oem_mb2.as...GM=717.433&CT=M&cat=503&SID=15&SGR=105&SGN=03

The Bosch ECU will probably be for the ABS. I can't think of anything else that'd need an ECU on an early car. My 1987 250TD didn't have ABS - it was an option back then - so yours may or may not. It's obvious if you do - there's an ABS block with hydraulic pipes on the o/s inner wing at the front of the engine bay

Nick Froome
www.w124.co.uk

 

[Zanimat]

Thanks for this - No, I don't have ABS.....but I'll have a look for the sender unit you mention! I'm suspicious of the fact that the tacho has failed at the same time as the idle speed has dropped......Malcolm

 

[Zanimat]

Problem solved!! I discovered that the ELR is, as was suggested, an idle speed controller and is supplied from another electronic module - the overvoltage protection relay, which is mounted next to it. This module has a 10amp Blade fuse visible through the transparent top. As I understand it, this fuse blows if too high a voltage is supplied, thus protecting the ELR.
The problem was that water had found its way into the o/voltage unit & corroded the fuse blades. There was therefore no supply to the ELR. I fitted a new fuse & used it to clean up the receptacles inside the unit with contact cleaner - (also the bits of corrosion round the pins) - and....Bingo!! I have correct idle speed AND a working tacho!
Cheers, Malcolm.