HI,

I have a 1985 300d that is great. I do most my own work because there are no local people to work on it. The engine and whole car has always had a ot of vibration (kinda like magic fingers). I had the compression checked, compression on three cylinders are right where they are supose to be. The other two cylinders are off by the same amount. I vaquely reading somewhere that the California version (has oxidizer and the air filter is more expensive) had some kind of bypass/ cutout to protect the turbo from back pressure? Could this cause of the two cylinders with poor compression and rough idle? Does this make any sense? More importantly, how do I fix this.

 

Before you do anything else, check your engine mounts. Maybe they are the source of the vibration.

What compression numbers were you getting, and on which cylinders? A bad valve adjustment can be a cause of low compression that is easy to check and corect.


Phil

 

Thanks for the reply. I have replaced the motor mounts and the engine shocks. I have had the valves adjusted, but still a strong vibrations. I don't have the numbers in front of me but assuming the cylinder are number from front to back 1,2,3,4,5, the 1, 3,and 5 cylinders have good compression. The 2 and 4th are about 10-20% off.

 

Notice any difference in the color of the injectors? Back, brown or varying shades of...ummm....pink?

Notice any bubbling in the radiator when the engine is running?

I would have expected head gasket, but I don't think so, based on the other cylinders compression. but it COULD be.

The vibration is definately coming from uneven explosions in the various cylinders, and that boil down to about three causes:
1. Fuel
2. compression
3. air (as in intake)

You have low compression in two cylinders, which could be caused by:
1. head gasket
2. valve adjustment
3. broken (or siezed) rings, or cracked pistons

Start with the simplest things first...double check the valve adjustment. I assume you have already checked that the fuel is being injected equally to all cylinders? (Just cracking an injector line at each cylinder should tell you well enough.)