my 95 fiesta diesel 1.8 turns over but wont start,?

1.8 diesel fiesta 95 model, trys to start and sometimes gets going, but sounds like it gives itself a boost of fuel ie, revs up by its self, and dies, had new glow plugs, on the occasion that it does get going, it runs fine once you let it warm up, had fuel pipe off and tried to turn it over, and although some fuel poped out, i didnt think it was alot, there is a box on this fuel line, which i assume is a relay, or ecu, could this be to blame and what is the funny box? fanx a bunch, john