Hello all;
I now have a 1978 280SE W116 sitting in my shop that started developing issues nealry five years ago. It started not, well, starting when it was raining or humid out, but fine the rest of the time. Then finally would not run at all. My first thought is Distributor or coil as a moist start issue would point to electrics as opposed to mechanical. Any other ideas? Just brainstorming out-loud here. It'll be a few days before I get my hands dirty on her, but i want to know what I am going after when I do. Thanks Guys!
-Matt-

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Currently:
1972 350SL Euro 4spd
1973 BMW R75/5
1981 BMW R80GS
1995 FZJ80 with OM606 Conversion In Progress

Hello,

I know I am replying to a very OLD post but did you ever find out what the problem was with the wet start issue on your 116. I have/had the same exact issue on my 450SEL. Whenever it rains or it is damp..which is rare in So. Cal. the car would not start. It turned out it was the distributer cap. Now that the cap has been replaced the car starts right up when wet or cold...but now it runs so rough and misses so badly that it can not be driven! As soon as the weather dries up the car runs perfectly??? Any ideas??? Thanks!

Hello Euro,

I'm sorry to say that we never really did figure that out. The car belonged to a guy that I knew at the time. It had been sitting for many many many years by the time I got to it and after we started work on it just became a case of the weakest link: every time we replaced anything on it the next weakest link in the line would fail and we ended up spending way too much money on it.

We had it running pretty good at the time of this post other than the wet-start issue. I think the last straw was that after we started driving it we were getting gas in the oil. And neither were resolved before I moved out of the area.

Sorry to be of no help. Maybe someone else can pop up and you some advice.

Cheers.

__________________
Currently:
1972 350SL Euro 4spd
1973 BMW R75/5
1981 BMW R80GS
1995 FZJ80 with OM606 Conversion In Progress

Thanks for your reply. My mechanic changed the distributer cap and cleaned the trigger points but still the same thing. I am going to try replacing the rubber boots and rewire the fuel injectors...then replace the spark plug wires...then??? It just drives me crazy when the car runs perfectly when it is not wet or raining out...which is most of the time in So. Cal. but I would like to rely on the car when it is wet or raining as well...Thanks again!

Okay, I replaced the rubber boots which protect the fuel injectors and rewired the fuel injector electrical connections to the injectors with new pins and connectors and so far the car has not developed the wet "missing" (almost like it was not firing on all cycl.) problem. And it has been really rainy here in So. Cal. so I think I resolved that issue... time will tell...

If it returns just use a spray bottle with water. With engine running just spray mist one suspect component after another until problem shows.
In the mid 60s german spark plug wires were somewhat troublesome with certain brands. They really disliked moisture after a certain time and the problem seemed to develop fast. At not really high milage. Just my experience and others may vary.
With a no start situation and dampness just spray them with wd-40 to find out. It displaces the moisture and lets the wires function properly again. Good test if they are generally suspect as well.