A strong edge coloring of a graph is a proper edge coloring such that no edge has two incident edges of the same color. Erdős and Nešetřil conjectured in 1989 that colors are always enough for a strong edge coloring, where Δ is the maximum degree of the graph. In the specific case where Δ=4, we prove this to be true when there is no subgraph with average degree at least , are necessary when the graph is even sparser.