I definetly feel that you are on the right track. I did my delivery valves, and prior to the repair, the engine could not be heard at idle. After the repair, there was slight nailing at idle and when going about 15mph and taking your foot off the throttle. There was no issue with smoke, nailing, or power at highway speeds. I redid the valves, and the nailing has almost gone away. In almost every post you read about the delivery valve repair, the writer indicates that after the job, nailing that was not present suddenly appears. The other area that would support your idea is the fact that when the engines are started from cold, as long as the glowplugs are active, the nailing is not heard. Once the glowplugs dissengage, the nailing immediatley follows. That would correspond with the idea of extra fuel getting to the injectors. As long as the glow plugs are activated, this extra fuel is no problem, but when they are deactivated, this extra fuel causes the nailing sound.

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96 E300d