'85 380 SL - White smoke - PeachParts Mercedes-Benz Forum

theobject · #1 03-21-2010, 05:59 PM

After 4 months sitting idle in the garage I decided to start her up. Started with no problems on first try, no hesitation.
I've been chasing a rough idle issue and decided to changed out the Bosch WR9DC platinums the shop put in 6 years ago with W9DC0 plugs. The plugs looked normal except for #5 which had black soot on it. I let the car idle for a few minutes and noticed white smoke from the exhaust which got worse with acceleration and left a black soot stain on the driveway. Took her out for a drive and white smoke continued to pour out. After about 5 minutes of driving the white smoke stopped and all appeared normal during the remaining 20 minutes of driving.
Started her up this morning, let it idle until it got to normal running temp. Again white smoke which got worse as the temp rose. Started driving with lots of white smoke trailing behind and after 2-3 miles/5 minutes the smoking stopped.
All fluid levels seem normal, no signs of oil in antifreeze and vice versa. Did some searching saw some threads on the transmission modulator diaphragm, cracked heads, valve stems, etc. I'm trying to troubleshoot this systematically.
Any advise on where to go from here.

Thanks,
Mike

bluewater · #2 03-21-2010, 06:21 PM

I had a similar problem when I bought my '85 380SL a couple of months ago. Mine was #4 cylinder that has a fouled plug. After trying different things to fix it (see this link), I still have a fouled plug.

What I did was that I jammed #4 injector so no fuel will go to the #4 cylinder. Run the car on highway for a hour at late night as it blows white smoke like crazy at the beginning. After 15 minutes, it clears up. Now I drive the car a couple of time a week and it runs fine.

I still need to find the root cause for the #4 plug. Until then, I can drive the car with 7 working cylinders.

bluewater · #3 03-22-2010, 03:09 PM

Last night while surfing the internet on different spark plugs, I came cross a spark plug that is typically used in motorcycles and marine motors. It has a shorter thread than regular car plug. So I went to a local auto store today and got a NGK (4322) BR8HS plug. Put it in the #4 cylinder and it works. Now the #4 cylinder fires well and I get much more power with all 8 cylinders working. So now, I am happy that a very simple solution fixes a big problem.

Attached picture shows the shorter NGK plug and a regular plug.

theobject · #4 03-22-2010, 04:14 PM

Interesting, what is the model # of the plug you pulled out?

bluewater · #5 03-22-2010, 05:16 PM

Quote:

Originally Posted by theobject

Interesting, what is the model # of the plug you pulled out?

I have tried a few different plugs before. They all ended up fouling. So the problem is the length of the plug thread. A shorter plug makes it hide in the plug hole so leaking oil (or whatever causes fouling) can not get on to the plug tip so it can ignite the cylinder.

strelnik · #6 03-22-2010, 06:46 PM

Quote:

Originally Posted by bluewater

I have tried a few different plugs before. They all ended up fouling. So the problem is the length of the plug thread. A shorter plug makes it hide in the plug hole so leaking oil (or whatever causes fouling) can not get on to the plug tip so it can ignite the cylinder.

Amazing. Anyone know if there's a Tech Svc Bulletin on this from MB? WHunter, any ideas for your faithful flock?

Your grasshoppers await your wisdom, Master

meltedpanda · #7 03-22-2010, 09:31 PM

probably no different than using a plug adapter that keeps plug out of combustion chamber . I put the adapter on my 220 and it worked great ( non fouler adapter).
An old old cure for worn pistons causing oil fouled plugs

bluewater · #8 03-22-2010, 09:52 PM

For some reasons, the non fouler adapter did not work for me. Maybe the adapter keeps the plug too far so it won't be able to ignite. The adapter solution gives me the idea of hiding the plug somehow from the fouling element.

theobject · #9 03-26-2010, 11:28 AM

I ended up bleeding the fuel lines off the FD and can tell that there was no change when I removed the line for #5. I'm going to replace the injector and see if that helps.

bluewater · #10 03-27-2010, 12:35 AM

Quote:

Originally Posted by partsman225

i bet you got a bad FD when you crack the lines one at a time does #5 shoot more fuel out of it. i had a 85 500 sl euro dumping so much fuel it was flooding the cylinder and smoking running rough,and spitting out water, it was the F/D the owner was so sure it was the head gasket ,he started to do it himself. he called me for advise,, i told him i didnt tell or dia. it has a head gsk you did, so long story short he had allready pulled the exhast manifold off it and the fan,alt brk, comp check it wasd good. fired it up with no exhast manifold ,there was gas shooting out the #2 cylinder #2 had more fuel when i cracked it , ,,,so i had an old line that a blocked off #2 so it had no fuel and the fuel stopped coming out the cyl. i got a new reman FD for 500 bucks car was fixed

the man so was happy he didnt do the head gsk, cause he would have ,had the same problem.. one of those people that thought he was a mechanic.

Did you measure the fuel pressure of #2 and compare with others? In my case, I thought that my #4 dumps too much fuel at first. But after measuring fuel pressure on #4, I found that it is similar with others. This test result leads me to believe that my FD is fine.

theobject · #11 03-27-2010, 07:58 AM

It did not seem like it was pouring out, however I loosened just enough to be able to detect a change so it was just kind of dribbling out.

Roncallo · #12 03-27-2010, 09:33 AM

Before you did any injector work did you try a bottle of Techron injector cleaner. If no do so. Every year I put a large bottle in my tank. When I have injector problems I use 2 large bottles to a full tank. So fat the 2 times I had to do this it cleared my injector problems withing 50 miles.