Problem with my 126. Can you help?

[revray]

Aloha from Hawaii,

I have two 300SD's... a 1980 (W116) and a 1982 (W126). I have run both cars with no modifications on 100% biodiesel (my own home brew) for just over 3 years. The 116 has performed without incident (have changed fuel filters a few times). The 126 has also run pretty well, until recently.

It idles and drives well for about 15 minutes, and then sputters and dies. Thinking that there was an obstruction in the fuel line, I disconnected the fuel line coming from the fuel tank at the engine compartment, blew it out with compressed air, and reconnected the fuel line. The car would start right up, but then sputter 15 minutes later and die.

Believeing that maybe some of my fuel hoses were deteriorating from the inside, I emptied the fuel tank and changed everything... both hoses at the tank (including a new tank screen), both hoses in the engine compartment, new fuel filter, and all of the injector return lines. I primed the engine, started it right up, and let it idle. About 15 minutes later... it sputtered and died.

Does anyone have a diagnosis?

Thanks in advance