PeachParts Mercedes-Benz Forum - View Single Post

hbofinger · #31 06-18-2002, 11:31 AM

Maurice - Nothing is as it seems. I just checked my car AGAIN. Here is something new I found.

1. Start car - runs a bit rough (A/C off, gear in P), around 650 rpms or so.
2. Put in gear. Rpms drop to 550 or so. Car runs smooth - perfect.
3. Turn on AC. Rpms don't change. Still smooth.
4. Turn off AC. Rpms don't change. Still smooth.
5. Put the gear back into P. rpms go to 1100 or so. Rough. They don't go back down until I put it back in gear. When I do, it's smooth again.

In the manual they attribute a high rpm usually to the air intake valve - the part I just futzed with. But would I then not also have a problem in gear? And why do the rpms stay in spec when the car is in P after starting, but go out of whack when I shift back into P after having been in grear? Could it be a bad switch somewhere?

On your car, the valve cover gasket - has the "C" modification been done to your heads? Mercedes came out with a set of instructions on how to modify the gasket surface of the heads afer they changed the material of the replacement valve cover gaskets. You need to deburr the heads around the area of the fuel injector seal holders. This is not in the CD ROM or manual - I found it on ALLDATADIY.com. It's a Benz technical service bulletin. Here is how the text reads:

As of May 1991 production, the above mentioned engines are
equipped with valve cover gaskets made from a new material.

In case of repair of engines prior to production phase-in, install only the modified valve cover gaskets. To avoid later leaks, the respective cylinder head must be reworked prior to installation of the gasket in engines 116.96/117.96. The procedure is described in this bulletin.

1. Remove install injection valves and insulating sleeves.
2. Close off bores (A) completely, e.g., with paper and carefully cover valve train as well as air flow sensor (Figure 1).
3. Remove any burrs surrounding injection valve bores (A) (i.e. using a hand grinder) (Figure 1).
4. Hone gasket joint face (arrows) with emory cloth/sand paper (100 - 180 grit) or oil stone to remove any shavings, especially in the area around the bores (A, Figure 1).
5. Mark reworked cylinder head with the letter "C" (Figures 2 and 3).

There are a whole bunch of diagrams - I recommend you go look it up. I have not found the "C" on my heads yet, so I refuse to remove the valve cover gasket until I am ready to do this...