I have a 1987 Mercedes 560sl. Has new fuel pumps, fuel filter, spark plugs, air filter, fuel strainer cleaned, fluids at proper level, and new brakes/rotors. Runs fine until I get to a hill. Then when I push the accelerator it bogs down and then dies. Continues this and will only idle. Any ideas what the problem could be?
I would have your mechanic redo the fuel pump pressure check and the fuel delivery check. By going through the full diagnostic tree most of the fuel system items and power supply can be check for good health. Once fuel delivery health has been verified, diagnosis on the CIS system would be in order.
When this happens, one thing to try is to release the fuel tank cap (just enough to let air in). One of the lack of fuel delivery conditions is a failure of fuel tank venting.
Does this vehicle sport the Bosch K-Jetronic mechanical injection system? Or is it an electronic fuel injection version?
If the mechanical K-Jetronic, I’ve had that exact symptom on a VW Rabbit with K-Jet, and it was always the fuel distributor clogged with grit. Did this happen soon after replacing the fuel filter? If so, that would further implicate a clogged fuel distributor. That’s something I can pretty much guarantee any mechanic who routinely services K-J equipped vehicles has seen before, and knows how to address.