Failing EGR Valve? - PeachParts Mercedes-Benz Forum

MB-Dude · #1 08-01-2007, 11:19 PM

At idle or low RPM's, hot or cold, dead-stop or creeping forward, my '96 SL600 has developed a rapidly pulsing 'thump' sound on the right-hand side of the engine; not in the front of the engine, but on the right side. It is not metallic (as if a rod or valve train issue), but instead sounds pneumatic. The thumping sound has slowly been getting worse. Car performs wonderfully, but the thumping noise is now noticeable and... speaking frankly... is a little embarrassing. Could this be the RH side EGR Valve starting to fail?

manny · #2 08-02-2007, 11:57 AM

Motormount?

MB-Dude · #3 08-02-2007, 01:14 PM

Quote:

Originally Posted by manny

Motormount?

Hmmm.... Could be - on the V12, the EGR Valve is directly over the RH side mount. However, I do not seem to have any other symptoms of motor mount movement and the engine at idle is very stable and smooth. Will check it out, though. Thanks!

Any other ideas? Is there a test procedure for the EGR Valve?

manny · #4 08-02-2007, 01:32 PM

If the engine is running smooth, I would'nt think it's an EGR valve problem.
Does your car have a Monovalve in the heating cicuit?
The have been known to make some strange, thumping noises, when the're opening & closing rapidly.

MB-Dude · #5 10-26-2007, 05:17 PM

To close on this one, the attached picture shows the disconnected vacuum line from ??? to a solenoid valve that feeds directly into the RH Throttle Actuator of the V12. The yellow pencil points out the disconnection. The 'thumping' sound was air being drawn in whenever the solenoid valve opened. As I noted above, the 'thumping’ was very regular and not timed to engine speed. I have no idea what the purpose of this solenoid valve is, and would appreciate it if anyone could enlighten me.

The '96 SL600 ran well with the line disconnected, and only a little better (smoother idle, mainly) after reconnection of the vacuum line. Of course, this makes sense being connected to the intake manifold. I found this out of frustration... just let the engine idle and kept poking around until I found something - perseverance!

Cheers,
Jeff