W123 economy gauge query

[cheesyget]

I have recently purchased a W123 200T and am working my way through all the little jobs that inevitably need sorting on a 20 year old car. As one might expect the central locking works to its own set of laws and I knew this when I bought the car. On the test drive the economy gauge worked normally but after a couple of days refused to move any further than 1/4 scale away from the red end. From the way the needle moves I get the impression it is vacuum operated - is this correct? If so has anyone solved a similar problem? I am assuming that the wayward locking ( who's habits have also changed since first viewing the car! ) and economy gauge problems may be related.

 

[cheesyget]

Problem solved !!

Have just found a split in the rubber pipe on the outlet end of the inline filter (?) near the manifold take-off. Economy gauge now works AND 2 doors plus the tailgate are locking! I love it when a simple remedy gives major results.

 

[pascal]

I was under the impression that the reading for the economy dial was related to the manifold pressure in 123s and early 124s.

Don't know where the reading comes from in my R129 (the same, spose).

Aeroplanes with Piston engines and variable or constant speed props have two readings for engine output, Manifold pressure and RPM. When the blade is set coarse at a given RPM the engine has to work harder than at fine setting for the same RPM. So we have Two levers one for RPM and one to control manifold pressure. The former being a bit like gears in a car and the latter the accelerator. Constant speed is a bit more complex but similar.

So what I'm trying to say is that manifold pressure is related to how hard the engine has to work and therefore directly related to economy.

PASCAL

 

[cheesyget]

Thanks for the reply. As I mentioned, replacing the split pipe from the manifold take-off cured the economy gauge problem and sorted out some of the door locking issues. Having browsed the forums for an insight in to the vacuum locking system lots of people seem to mention vacuum pumps but (a) I can't see one anywhere and (b) why have a pump when the engine creates vacuum pressure of its' own to keep the resevoir topped up? I've never worked on a car with as many manifold take-offs!

PS No problem with theory of VP props - just got my frozen ATPL!

 

[TimN]

You will almost certainly find that the other two doors have a split in the diaphragm on the central locking slave units. As a temporary measure you can remove the pipes and block them with a suitably sized insert. The door ones come in al about £21 the tailgate abot £27

Tim

230TE W123
Honda CB 750 F 1981 all boxed

 

[pascal]

The 123 has a completely different system (as far as I know).

I do not think it has any electric pump for the CL system. It has a vacuum resovoir run off the engine.

As I mentioned earlier the pipe from the manifold contols economy gauge for the purposes of the other tread running along side this one.

 

[pascal]

Forgot

Forgot to add,

Auto boxes use vacuum for smooth changes

Bosch KJetronic fuel injection systems, take vacuum reading from inlet manifold.

Turbo-diesel engines inlet manifolds do not create vacuum.

Diesels engines have a pump (mechanical?) to create this vacuum.

So far we have inlet vacuum supplying:

• Heater flap to demist
• Heater flap to feet
• Headlight control LH
• Headlight control RH
• Auto gearbox
• Fuel injection system
• Economy gauge

The above may not apply to all MBs, but I'm trying!!!!!

Come on now boys. Help me out here. I'm doing my best.

Pascal

 

[w123robbo]

Where abouts is the valve on the manifold? My W123 eco gauge has stopped working after not being used for a while.I startedit there was a pop then the gauge stopped .Can any one help?

 

[television]

The theories above are not that accurate,, I have answered your other post