My 1981 300D exhibits what I assume is fuel starvation on lengthy hills. Becomes jerky. Runs excellent at other times. I've replaced all filters (including tank strainer) and drained the tank. Has new Bosio injector nozzles, but the problem is essentially the same pre- and after-nozzle replacement. 198K - has been well cared for (by Mercedes for a good part of life with its former owner).

Any ideas?

Bad lift pump?

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Agreed.

Everything else has been ruled out. The lift pump must be marginal........works fine for all conditions except maximum power.

My only reservation is the term "lengthy" for the hills. If the pump was the culprit, the problem would show itself very soon after maximum power is demanded on the hill. If there is a delay in the onset of the symptom, then I might think again with regard to the pump.

In any case, the pump has a specification for flow rate..........worth checking.

Might be the primer pump rather than the actual lift pump.

..........air leaks.........???

Yeah, the higher draw for fuel may be pulling in air through an otherwise marginal primer handle seal.

If it's the old primer, it's time for the $20. replacement anyway..........cheap investment to possibly solve the problem.

Has recent old version primer pump, not predating the problem, but then problems often like company. I'll try tightening the primer with my crow's foot - a tight spot to work in.
At least eliminate one possible culprit.

Thanks to all!

Erlend