300 E fault that the Serv. Officer does not resolve

Hello. I have an old Mercedes Benz Model 300 E, from 1998 who works perfectly, starts the first and sounds like new. It really goes very much but it has a breakdown that not even the office office has been able to solve. The breakdown is that at least you expect the engine. After 30 to 60 seconds you give the key and start without problems. This does it cold and hot, they can pass two days and do not do it or in a small 10 -kilometer journey does it twice. I have taken it to two official Mercedes services, in one they had 15 days and they did not find anything, they say that they did not fail them, around the workshop he stopped again. Take it to another official service and more of the same. He continues when he wants. What can happen to me? Thank you

They changed the phase captor?

I am not sure that this model carries phase sensor if you can pass me chassis and engine type
I will study the system and I will be more rightly, but if you did a test we were doubtful, first when you stop checking that the fuel electro-pumps sound, since they carry two and if they did not make it a punket in the relay of these between the terminals 87 and 30, I hope you serve you.
Greetings from Tenerife.

Look that the injection relay does not have false welds that when reheating produce lucky cuts and keep me informed.