I have a 1985 MB 280SE (M110 engine) totally rebuild, and till now it ran perfect!
One day the idle was rough like it turned on only 5 cyl, and now I cant even start the
engine anymore. There are sparks, and gas
I changed the electronic module but without result.
Could it be the distributor? How can I test it?
Where to look first?

Thanks for any help,

Marexke,

Did you check distributor cap or rotor? I've seen some rotors that had a hole burnt in them, underneath rotor where it attaches to distributor shaft. Or a cracked distributor cap causing a cross firing~ electricity not going to correct plug at corrct time. Electricity takes the path of least resistance. This what I would check.

If you had spark, why change the ignition module? To check the distributor on the car (basic check), you should be able to turn the rotor clock-wise about 15mm or so. When you release it, it should "spring" back to the original position. You can also use a timing light to check the timing at starting speed while someone else cranks the engine over.
The M110 engine does have a unique problem with wear on the drive gears for the distributor and oil pump. Commonly referred to as the "matched gear set". They can (and do) wear enough to cause the distributor to "jump" out of time. That sounds like what has happened. Replacement of the gears requires removing the cylinder head.:(
Regards,
Randy D.

WDURRANCE,
the drive gears for the distributor and oil pump are O.K. I checked it and like everything else, advance,sparks,sparkwhires, distributor cap and rotor, green whire,are in perfect condition!
When I trye to start the engine,it almost runs but sputters and has detonations like the advance is not right!
Any advise???

Just a wild guess but I noted you said it gets gas but could the problem be due to fuel starvation? Have you checked that the fuel pressure is adequate?