The 280SL was a euro-only car. The early euro M110 motors were electronically fuel injected (the D-jetronic system), as were ALL the M116 & M117 motors (the 3.5 & 4.5 v8s) and period volvo's, saabs & VWs.
Benz never shipped the M110 versions to the US, so the available doc is pretty scant. BUT, the v8 service manual has most everything you want to know, as do some of the books on older fuel injection systems. Lastly, the M110 service fiche has section 7.4 that specifically covers the system.
According to my 1974 TDM, the 280SL was built as-of Aug 1974, so having the D-jet system is perfectly OK, if you car is old enough.
Some people consider the system a real pain, others less so. You can spend a great deal of money swapping out parts to figure out what's wrong. DON'T do that. There are published diagnostics to follow. If you email me (I've already sent you a mail via this site), I can reply with what doc I have already scanned magnetically.
Read the docs and then use them and be patient. The system's biggest failures are:
- poor electrical connections (look for and clean the ground point from the harness).
- vacuum leaks (check VERY carefully. REPLACE the hose to the manifold pressure sensor)
- ignition system & valve clearance problems (get things to SPEC).
Lastly, anybody that suggests that you REPLACE your "trigger points" should be smacked. Rarely if ever do they need to be replaced. However, they probably haven't been cleaned. They do get dirty. Use a little contact cleaner spray, once you find them and figure out how to remove them. Then put them back.
Also, check this site, in both this forum and the vintage one for other postings related to the D-jet system and the woes various folk have had with the 280se 4.5's & 250CE's.