Mercedes Benz repair: 91 Mercedes 420 SEL, mercedes dealer, fuel mixture

Question
91 Mercedes 420 SEL starts, runs for 2-4 seconds then dies.  Had the same problem 2yrs previous - took the car to Mercedes dealer & car was repaired.  This time around took it to a different mechanic.  Fuel lines have appropriate pressure.  Replaced fuel relay -  no change.  Am at my wits end.  This seems to be an electrical problem, but not for certain.  Input greatly appreciated.

Answer
Greetings!
 Sorry about your problem! Well First , you want to check if it is in the fuel or firing. Take the breather off with the two little ten MM nuts.Take your finger and push down on the air horn with the key on. You should hear a squeak when the fuel is squirting in the plenum(intake). Also see if you hear the fuel pump run when first turn on the ignition.Then if all is good, Get someone to turn the engine over with a plug wire removed and a plug stuck in it and grounded to the nearest point. If you are getting fire, Then you probably have a problem with the fuel head. See if you can make it run by shooting a squirt of starting fluid in there and trying to make it run. If you can, then you may be able to adjust the fuel mixture and make it run. There is a tower just to the back of the air horn, and in front of the fuel head ( 8 fuel lines go to this). You have to have a long 3mm allen wrench. Pushing down on this and turning it clockwise richens it and counterclockwise leans it.
These models are also bad about the roter buttons burning up on them and very sensitive as to which kind of plugs are in there. Bosch Supers are reccomended on this model and not the platinum.
If you need more help just ask. Thanks and i hope this helps.Ricky