23
« Last post by cjpoulos on April 03, 2025, 13:07:40 »
Hey all. I have a 1969 Mercedes 280sl that I brought home in June of ‘24. I’ve been chasing down some demons ever since I took ownership, and I like to think that I’m mechanically able. I’m having some pretty tricky rough idle and rough running (when it feels like running) issues. I’ve search through the forums and pieced together info on many issues, but I felt like it would be worth it to make this post. This car is verified to have only 14,800 original miles, but it was stored nicely in a garage in non-running condition for 25+ years. It’s in amazing shape cosmetically, but it’s not the best mechanically at the moment. I’d love some advice on changing that last part!
Here’s a list of the engine related work I’ve done minus a few things:
Replaced Fuel Tank
Cleaned Electric Fuel Pump
Replaced All Soft Fuel Lines/Filters
Cleaned Hard Fuel Lines
Verified Functionality of CSV
Valve Adjustment
Valve Seals
Compression Test - All cylinders hold about 160psi
Cooling Channels Cleaned in Block
New Water Pump
Throttle Linkages Are to Spec
Valve Timing and FIP timing are set to correct spec
There’s lots more necessary work that’s been done to revive this car with the goal of preserving it and ensuring it’s health for many miles to come.
Now, the engine cranks well. It will typically start quickly on the first go. It idles POORLY (makes a deep rumble too). Maybe sitting at about 500rpm idle, does not like to rev up, and does not smooth out at higher revs. It tends to die after about 30 seconds. At a second attempt, it cranks but doesn’t start, although it tries. By the third attempt it only cranks. I don’t crank it for very long obviously, but I can’t figure it out at this point! The plugs are fouling with carbon very quickly, they’re gapped to .030, and black after maybe 30 seconds or running. I know these cars like to running rich, and maybe it’s just because there is excessive fuel when attempting to start, but that seems like a short amount of time to foul plugs.
Like I mentioned I’m an able mechanic and like to think that I’m not a hack, but this car is kicking my ass! There is also some fuel in the distributor vacuum line if anyone has some special knowledge on what that may cause.
I’m definitely missing some info here and I would very much appreciate some advice - and if I mentioned something that you know to be very wrong, please tell me! Thanks!
Recent Posts