I recently bought a 1986 560SEL. The engine was rebuilt (completely) at 212,000. The transmission was serviced at 195,000. It sat dormant for 4.5 years because the original owner had the engine rebuilt ($2,300 worth) and the tranny started acting up. He got digusted and parked it. Took him 4.5 years to decide to sell it I guess. I bought it, found a disconnected vaccum line under the passenger side of the airbox and it ran GREAT for 3 weeks.
The only parts I replaced to get it running (and home) were the high-volume / low-pressure fuel pump and the fuel filter. The old (original pump) had black old-gas sludge in it. I know I need to clean the tank (I was just foolishly hoping to melt it out).
Here's what's happening, it starts and drives fine at low speed but if I drive up hill, and the transmission needs to downshift, it starts to stutter and die. The engine tries to recover but it rummbles and it usually can't and it dies. If I turn it off, and then give it to short (1-second) bursts of the starter (to engage the initial fuel pump cycle) it will start and run fine for about 3 more miles up the hill, then it stalls out again.
Another way I can MAKE it act the same way, whether going up or down hill, is to press the gas pedal into the kick-down switch. It will surge violently (lifting the nose of the car high and then dropping it). It's like it can't decide between the gear it's in and the passing gear. It will do that until I let off of the switch or until it fuel-starves again and dies.
Both fuel pumps are working, checked those. Haven't checked fuel presssure yet (doing that now).
Do you think I have more than one problem, or just a dirty in-tank screen?
V/R, -Charles
PS - LOVE work you're doing for us old Benzo fanatics!