Knocking noise on 92 400e
 

My 92 400e w/ 70K miles makes rapid knocking noise under acceleration when the engine is cold. When temp gauge reaches above 80 degree, oil pressure gauge drops 1-bar at idle, the knocking noise seems to disappear. The noise started recently after check engine light came on. My mechanic changed the trans boden cable, because that's what the diagnostic code shown, but the problem still persists. Another mechanic suspected "carbon knock" and suggested fuel additive to burn off deposit build up on piston and valves. Any help and suggestion would be much appreciated.

First off,

Welcome to forum and happy holidays.

Try doing a search on the site, searching for things like knock, knocking, etc etc.

Also check for oil. When is the last time it was changed. what is the viscosity?

Also what grade fuel are you using?

Have you run any injector cleaner in it?

These are all things that if not done should be checked and or done.

Alon

These are what I use now, same stuff on my last 89 MBZ 300e:

Castrol GTX 20-50W Oil, Shell 92-Octane Gasoline, BG 44K Fuel Additive.

the 44k should clean out most of the carbon in your system. I believe the trick is to add it, then drive the car hard to get it to spit out all that carbon..

The oil, might be a little thick.

I use 20/50 as well, and my car makes a ticking on cold startup for a few seconds until the oil pressure builds up.

A Thinner viscosity oil might help it circulate more for you.

I would definately do some searchign on this site, you might find your question has already been answered.

Alon