The service manual states reasons for code 0707 P7 as:
Harness or Connectors
Electronic Control Fuel Injection Pump
Improper Fuel Quality
I ran it out as much as I could, then dropped the tank, hoping for a bit of improper quality fuel. It wasn’t bad at all, with just a small amount of black floating around (fingerprints mine).
I pulled the filter (400 miles old), which had nice, clean diesel, but also a couple of big chunks of gunge.
Now. I disconnected the fuel lines at the filter, attached a water bottle with holes drilled in it to the tank end, and blew them out with a compressor. And this is what came out of the main fuel line.
Quite a difference. It was as opaque in real life as it looks in the pictures, and a lot more jet black diesel ended up on the garage floor. I blew the thinner pump return line out into a rag, and it was pretty much pure black solids with a little liquid.
After refitting the tank, replacing the rubber pipes at the tank, half filling it with new, name brand diesel and Exocet diesel anti-bug, it was primed up and taken for a good, hour long blast up and down the A-roads to blow its nose out, which went without a hiccup. I wouldn’t say it has added any power, but the engine now seems a lot happier at the top end.
So, I’d say blocked up fuel lines were my problem. I’m still going to put a few hundred local miles on before venturing too far, hoping that no permanent damage has been done to the pump. Of course using a regimen of quality diesel and bug-killer.