My 93 after running for an hour or so has a significant reduction in power. It acts as if it's staving for fuel, so blows black smoke when I accelerate.
Really doggy when I leave from complete stop. When it sits for an hour it runs like a new car. Checked the tank filter and replaced the inline and primary filter, no change. It actually acts when it is having a tantrum as if the turbo is failing. Had that checked and for $85 bill informed me it was perfect, probably an injector pump. Took it to a pump man, he laughed and said if it were the pump it would be obvious and that these pumps run at such a relatively low pressure they hardly ever fail. Plugged the EGR line, no help.... Last possibility that I can think of is the lift pump on the lower right side of the engine, easily removed and I'll have it rebuilt tomorrow. Any other possible causes you can think of? Thanks

Lift pump?

I'd hook up a boost gauge and see if max pressure to the ALDA is lower at operating temperature.

Sixto
95 S420
87 300SDL