Is a Diploma holder in ECE with four years of work experience eligible for MBA or PG Diploma from any university?

Sorry. A diploma holder is not eligible to do master/post graduation courses unless he or she completes a degree course. You can go for degree/post diploma or short term courses. All the best.

You are not eligible to seek admission in MBA unless you complete any graduation degree with 50% or more marks. Diploma with expereince is not equivalent to graduation degree awarded by Universities.