Need help on my Jetta

I have a jetta 1987 and one I was driving the car went off when I was driving and won't start after and I have a friend that look at the car and I take out the fuel fitler and check it and see if it was clog but gas came out and little black sand or stuff came out and he said check the fuel pump and it work and I look at the fuel distributor and take on side of the injectin and see if gas is coming out but not a thing I take out the fuel distributor and clean it inside and out and put it back in and I start it up now it work start still do you know what might be the trouble here