hello,
I'm new here.. i have a '80 450 SL R107 that has a crnks, runs 5 seconds then stalls issue.. it has had the fuel PKG, injectors, injector sleeves and fuel tank screen replaced... after the injector replacement it started and ran for about 10-15 seconds then stalled again. it will run on fuel cleaner or brake cleaner smoothly.. the fuel pump only has power when cranking not with key on engine off. i was told to check the fuel pump relay and a fuse but getting mixed info on where they are located. does anyone know where i might find these 2 relays and fuse? also not sure if it matters or not but the fuel level sender stopped working just before it started doing this.

I would start with doing a smoke test on the intake manifold and checking the fuel pressures. Your car is unique in that the 1980 model year was the only year that the 450 motors got the oxygen sensor and the frequency valve

The fuel pump relay is located behind the RH kick panel. Remove it from its socket, and look at the numbering of the relay pins. The socket sleeves that correspond to pins # 30 & 87 are to be bridged with a jumper wire. Does the fuel pump run continuously? If yes, start engine.