The sentences is grammatically incorrect because there is no coherence between the action and the period of time.
"desde hace mucho tiempo" might imply that I am still working there. it is like "I have been working here for 4 years". and the verb "trabajé" makes reference to a past action, you do no work there any more.
So the correct version of the sentences might be " Desde hace cuatro años trabajo ahí" (if you are still working) or " Hace cuatro años trabajé ahí" ( if you don not work there anymore.
