Problem is with the Fuel Injector Pump.

So what was the problem did you fix it

Left chamber in the injection pump has issues. Also the injector looked like it was spraying too tight of a pattern, but may still function properly.

So only the one injector was firing, but when you swapped injectors the problem did not follow the injector itself, so maybe the problem is in the control system.

injection pump

2GM Yanmar. Common common problem with them is one plunger in injector pump will stick/seize, delivery valves can and do stick and delivery valve springs will break. They also break plunger springs, then can break the tappet roller but its rare.