2.4 injector problem

[Nikola78]

Eml light on, vdc not available error on the dash, particle filter light on, diesel gauge going up and down, 3ngine going really bad.
Ecuscan shows error P0204(injector 4 faulth).Cleaned the injector connections with contact spray, cleared the errors with fiat ecuscan,was running good for a week and then all over again same thing.
Did the same procedure again, couple of days of a good run and it came back again.
Any ideas whats the problem?
If its faulthy injector, I reckon it wont be on and off situation.
On other forums suggestion is that it might  be the electrical/wiring issue, my mechanic says to change the injectors.
Help needed.

[Craig_m67]

Have the battery load tested
Check alternator output at various rev ranges

Dodgy fuel gauge sound like a bad earth
Any other symptoms?

What did you/somebody last touch??

[Nikola78]

Nothing has been touched lately, was oversees for a month, couldnt wait to come back just to drive my bella and this shit happened. Never had a huge issue before, last and only thing was dmf change in october. :/

[phri]

Fuel line / filter partly blocked? Some moisture in tank?