Please help! Going to give this one last shot before throwing myself on the mercy of an MBZ shop. Here are my symptoms:

1. Miss and pinging at idle when cold. Turn on glow plugs, miss goes away.
2. Pinging like a gasser at part throttle at all engine temps, much worse when cold. Only pings at certain throttle positions when warm, like when cruising down the road, then it sounds like I have ball bearings in my cylinders. Give it more throttle or let off the throttle entirely and it goes away.
3. Loud clacking or metallic noise when off throttle and coasting down in gear.
4. All of this is getting worse.

I have:

1. Greazzer rebuilt the injectors. Twice. I'm confident they're fine.
2. I set the timing using the drip method. No difference. I moved the timing in two degree increments backwards and forwards until the engine wouldn't run in either direction. Pinging and miss still present at all timing settings.
3. Killing individual injectors does not change any of this.
4. Ran the engine off a bottle of fuel in the engine bay, observing fuel returned to bottle for air bubbles and such. There were none.
5. Ran two cans of diesel purge through it. No junk came out in the bottle, no change in running when switched back to diesel.
6. Valves have been recently adjusted, compression was decent and even across all 5 cylinders.
7. Glow plugs all test fine. They were viewed in the engine with the injectors out, tips glowing brightly.
8. Been through a mess of filters.

What am I missing? Did I fubar my injection pump during drip timing?

Thank you all. Really scratching my head over this one. There's a local-ish guy who's been working on MBZ diesels for 40 years, next step is dropping it off with him.

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617 swapped Toyota Pickup, 22-24 MPG, 50k miles on swap