I have a 1970 280 SL that will not run. The car was my dad's and has sat for probably 11 years. I decided to take it out and run it a little. It was a little hard starting but it eventually did. It ran terrible...missing and smoking like a diesel. I changed the plugs and drained all the gas and put new in it. I figured this would cure the problem but it only made it about a mile down the road and did the same thing. I barely got it home and took the plugs out again and found they were all filed bad..absolutly covered in soot. The car smokes black smoke so bad you can hardly see behind it. I have no idea what to do with it next. I was thinking maybe the rings are stuck from sitting so long but i really don't know. Any input would be greatly appreciated.
Thanks

First, replace the spark plugs. Bosch plugs usually won't recover from carbon fouling very well, if at all, so if you ran it with rotten old fuel, they fouled and now won't spark properly.

Put some redline fuel treatment (or Techron if you can't fine RedLine) and jumper the fuel pump relay so the fuel pump runs, and let it run for a couple hours.

You have two problems - the injection pump is probably stuck and overfueling, and the fuel is terrible, even with draining and refilling. Burn off all the fuel you can, and hopefully the Techron or RedLine will free up the IP fuel control rail and restore normal function.

You can free the rail up (directions in another post on this site) but BE CAREFULL and don't attempt this if 1) you aren't good a fixing unknown mechanical stuff and/or 2) have $2500 to spend on getting it fixed if you screw it up.

DO NOT attempt to adjust the fuel mixture and DO NOT mess about with the linkage, you will damage the pump if you adjust it with the engine running and getting the linkage re-adjusted will drive you nuts. The mixture is determined by engine speed, throttle opening, and temperature -- needless to say, it's complicated!

You should also check to make sure the coolant level is OK, and that the thermostat works -- these beasts run RICH cold, and if the warmup regulator is bad or the engine temp doesn't come up (or the coolant is low and the regulator doesn't heat up), it will foul the plugs.

There is also a possiblity the cold start valve is stuck open -- Redline or Techron will cure that, too. If you jumper the fuel pump, watch for flooding. Cycling it on and off with a jumper may free it up -- I don't know if they are still available. If they are, they will be very expensive.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

I went through this with a long-sitting (five years) 230SL with a 280 engine in it. Peter's suggestions are worth a try, but I think you should start looking for a used or rebuilt injection pump. We put hours and hours into trying to free up the injection pump but in the end the peanut butter residue of the fuel won out.

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

Thanks for the help guys. I will definatly try the fuel treatment and cross my fingers and hope lol.