Bobcat 843 Surging - Injector Replace Question

[Auggie]

Hey there-
My 843 from the early 90s started surging badly the other day and feels like it will stall out but I can limp it along. The surging sound is quite cyclical, and there is some black smoke from the exhaust but not too bad. I use it for farm chores, so it's not run heavily, but I bought it from a local landscape guy who was hard on it. he bypassed the original fuel filter with just an in-line filter, and I understand that some of these systems can be sensitive to bad filters, although it's run fine so far for probably the 100 hours I've put on it.
I checked through the fuel system up to the injector pump: I checked the pickup tube, it didn't have the screen thing on the end, so I popped one on. I blew out the fuel pump and tested it pumping diesel from a small jar, also confirmed it has 12V at the fuel pump while running. Changed out the in-line filter with a new 'heavy duty' one. And I blew out the hoses as I went. Also took off the air filter and ran it, and the problem persisted.
Now I just pulled a fuel injector and the tip looks fouled, so I'm going to just get a new set of injectors (unless someone wants to advise a good way to farm-clean the injectors and pop them back on). My main question is if there could be sediment or issues in the injector pump that might work its way into the new injectors after I replace them. Or could it be something other than the injectors? Also interested if there is a way to salvage my current injectors.
Thanks

 

[Auggie]

Well, I replaced all the injectors but it's still surging when throttling up and there's no power. Idle is smooth. Here is a link to a youtube video I took of the sound (). Am I looking at rebuilding the fuel injector pump at this point? Any tips are appreciated

Thinking there might be air in the line, I bled at the injectors but fuel spewed right out, and the sound continued. There is no priming bulb, but the fuel pump makes starts pretty easy after working on the fuel line.

Thanks

 

[laurencen]

that sounds more like a metallic sound than fuel related, can you add a pressure gauge into the fuel line?

 

[Auggie]

Thanks, that's a good idea - would that be anywhere between the lift pump and the injector pump inlet to check the lift pump? Or would it be between the injector pump to test that?
What psi am I looking for? And would I tee it in to see psi while it's operating, or would I basically deadhead the outlet of the pump with the gauge and crank to see the max pump psi?