I have a 91 350 SDL that I had the injectors rebuilt and balanced to within one bar. I reinstalled them with new washers taper down torqued to 60 lb. ft. I installed new OEM glow plugs, and I did all of this in an attempt to get rid of the smoking at cold start-up. I ordered today, a set of pressure valve washers and o-rings with the understanding that maybe one valve is applying too much pressure to one or more injectors ? The engine puts out GREAT power and is quiet above about 1300 RPM and is super smooth. It also has, what I think, is more knock at idle than another 3.5 that I listened to yesterday. The engine, when smoking at cold idle also is very rough. Any help here is much appreciated.