This is a copy of a message I posted to the MBZ.org diesel email list:

===========
Hi all,

While doing some other stuff to my second (running) 300D, I finally tried disabling the "cruise surge fix". This was an add-on to reduce cruise control surging on hills, or some such malarky. It was due to the operation of the EGR and/or air recirc valves, I believe. If these have been disabled, it's my opinion that the cruise retrofit is unnecessary. For the record, on my first 300D, I NEVER had any surging - and that car never had the retrofit installed (still just 2 s/o valves - this car also has the EGR & recirc disabled.)

How do you tell if you have this? Look at the plumbing between the intake, ALDA, and tranny valve. Normally there are only 2 switchover valves. The cruise "fix" adds a third, with some restrictors and a filter. I disconnected the third with it's plumbing. It should go from intake, to overboost s/o valve (#1), out to ALDA, and "Teed" from there to the tranny switchover valve (#2, which softens cold shifts).

I did this temporarily and from the seat of the pants, it feels like there is significantly more power from ~2000rpm up - basically where the turbo is working. I believe the restrictions limited, or slowed, the signal to the ALDA and therefore reduced fuel enrichment. Marshall mentioned this a while back. Oddly, the first time I stomped on it and the boost came up, I got a MASSIVE black cloud out the rear for about 3 seconds. And this car NEVER smokes like that. It did not do this on subsequent throttle mashings, and has not since then. Hmmmm. Anyway, I think I might reconnect it to try to verify the improvement, then permanently disconnect the "retrofit", and remove the valve and assorted plumbing. I'll try to take some pictures too.

Note: The retrofit installation is explained in detail in the OM602/603 engine manual. Look in there for diagrams and more info. But I recommend anyone with this "fix" in place at least *try* disabling it, you might be pleasantly surprised!

[:-)

__________________
Check out my website photos, documents, and movies!