I have 1992 f-350 7.3 diesel pickup it was having problems starting turns it had four glow plugs burned now it starts fine. I had not started it for several weeks when I started it it has a knocking sound I think it might be an injector how can I find out if this the problem or what might cause this knocking sound. When I started it it wasn't knocking after about two minutes it felt like it was going to shut down then the knocking began.