Hosted on my site also here:
http://www.w124-zone.com/articles.php?article_id=41
I thought I'd add it here for you guys to enjoy also for those who have not done it, and more than likely NEED to
----
Fuel Filter Replacement
First off, the importance in changing the fuel filter is second to none for the CIS-E system. It is almost as important as changing the oil on time. The fuel distributor and EHA heavily influence the running condition of the entire engine and are very expensive pieces. The fuel distributor has a micron filter built inside of it which over time collects deposits from old fuel clogging it and reducing performance. This is the reason why replacing the fuel filter is very, very important.
You don't want to have to get the fuel distributor rebuilt any sooner than it has to. It also is very difficult to diagnose since fuel pressure will not neccessarily drop. With my clogged distributor, I noticed a lack in performance and fuel economy, but fuel pressures were within spec. It can make you go crazy
As with all filters, stick with Bosch or MB. Do not get a FRAM or any of those junk filters. The whole point is to limit long term buildup in the distributor, if the filter is not filtering its staying in the distributor, it won't just get blown out the exhaust. (This is the reason why fuel injector cleaning seldom does anything for Bosch CIS-E system....not all, but most dirt doesn't even get to the injectors -- it gets stuck in the distributor.
Difficulty + Cost: Easy with the tools mentioned below. Filter is ~$15.
Change Interval:
Every 30k miles. MB calls for 60k, but experience with CIS-E dictates 30k miles is THE best interval without question. Do not follow a 60k interval.
Additional Inspection - Replace if needed:
Copper crush washers upon removal
Rubber donuts for cracks/aged that hold the pump, filter and accumulator in place
Protective cover for fuel leaks at any of the 3 units.
Tools Required:
Jack
2x 17mm wrench
19mm wrench
10mm socket and extension.
15-20mins job
GERMAN fuel filter. Bosch is perfect.
Procedure:
Factory PDF:
http://www.w124-zone.com/downloads/MB%20CD/W124/w124CD1/Program/Maintenance/My81/0780.pdf
^ 103 is several pages down. I believe this article covers more than the manual does.
Begin by jacking the car up, you can get away with simply jacking up the passenger rear. Remove the (4) 10mm nuts that hold the protective cover in place. I took the opportunity to completely degrease and scrub clean the cover since I elminated all my oil leaks. You can see the difference....
Clean:
Cover off.
Left = Fuel pump
Middle = Fuel Filter
Right = Fuel accumulator.
Wagons and later models utilize a second fuel pump. The wagons is located in front of the gas tank underneath a small protective cover also.
Counter hold using both 17mm wrenches and crack free. Minimal gas should come out. Check all fuel lines for cracks. I noticed that mine have started to crack, so its on my next purchase order.
Use the 17mm to remove the bolt from the banjo fitting. There are (2) copper crush washers that you should inspect and replace if neccessary. They go on either side of the banjo fitting. The removal of this side of the fuel filter will lose all the gas residing in the filter so have plenty of rags or tissues to catch the fuel remaining in the filter.
On replacement: Counter hold using the 19mm wrench on the filter itself. If you do not counter hold, you cannot tighten this side enough and it will leak. I know how I found out.
New filter going in. The best way I found to do this is to REMOVE the plastic cover you see on the filter and place it in the filter housing FIRST, then slide the filter in otherwise its tricky and not worth pulling on the rubber donuts that may be getting old by now anyway.
New filter in place and everything tightened up.
Get back in the car, turn on the ignition, engine off and check under for leaks (initial may NOT show leaks -- filter is empty!)
Crank the car, it may take 10-20secs of cranking for the filter to fill up. Once car is running, get back under and leak inspect again. Turn car off, repeat to double check. Run car for a couple minutes at least before putting protective cover back on.