Black smoke/rough puzzel - 560SEL 1989
 

It will work fine when I disconnect the EHA switch but when I connect it I need to realigne the fuel distributor and will work for a while then black smoke again and rough idle/cutting.
It's really annoying. I changed the followings:

Spark plugs
Injectors
Spark plug wires
Fuel filter
Fuel accumulators (Front and back)
EHA
Fuel distributor

I checked the followings and they are all good:
Fuel pumps/pressure
No oil in sparks
No vacuum leaks
O2 sensor
Fuel pump relay
Cap/rotor
Engine timing

Could a new EHA valve be faulty?

Mainly, what could cause the black smoke?

Now the problem is occurring even when the EHA valve is disconnected. It's occasionally shaking a bit and surging.

Can someone give me the best test of a vacuum leak and where to test the leak? Thanks in advanced... It's a real puzzel for me.

Have you checked the on/off lambda ratio and current at the EHA?

No I did not and I don't know how to check them. Can you help me please? :)

Do a search for tons of info.

You could start here:

click here

OK. I cleaned the intank by adding carb-cleaner in the break booster hose and the engine absorbed it. After that I realigned the fuel distributor while the EHA is connected. It's running fine now but with a little occasional surge on the highway. I'm suspecting a bad O2 sensor. Anyway it's not available in Kuwait. No more black smoke.

Can I add carburetor cleaner to the break booster hose for my 600SEL 1992 as well or it may cause troubles?