I have a 1991 300D and 350SD.

The 300D has injector knock on injector/cylinder #1.

The injectors were refurbished. No change.

I swapped an injector from my quiet and smooth 350SD, and the 300D worked fine. So then I bought a “good used” injector. It knocked.

So then I took a different injector from my 350SD, installed it, and it too knocked. It doesn’t knock on my 350SD, but it is knocking in the 300D.

I always torque to 70nm. I bleed air. It’s plain to see when I crack the injector feed line that the knocking stops.

First I thought it was bad injectors. There could be two bad ones.

But now I have to wonder if somehow it’s me. It’s not like I haven’t swapped a lot of 60x and 61x injectors before. I have.

But could there be something I’m doing, or something with the hard line or return lines, that maybe I’m missing?

I do notice in the clear viton that there is some air in the return line. But it was also there with the quiet 603 injector I swapped….

Thanks for any guidance.

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Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (116k)
1991 350SD (206k)
1991 300D (228k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (267k)

Past Diesels:
1983 300D (228K), 1985 300D (233K), 1993 300D 2.5T (338k), 1993 300SD (291k)