W124 Fuel Filter Replacement DIY

[ps2cho]

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

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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.

[tbomachines]

Just a note for future - some W124s have a dual fuel pump design so it might differ from the pictures. Good writeup and pics

[JohnM.]

Just did this last week on my dual fuel pump 91. Process is exactly the same. This should be added to the DIY WIKI. It was one of the few things for the W124 that's not in there, even though it is a simple job.

I've never touched the filter on my car and I've owned it for 60K. I'm guessing the old filter had at least 100K on it, if not more (oops).

[long-gone]

When I did mine I pulled the whole assembly out. It's very simple - remove the battery pos cable - remove the electrical connections from the pump/s - remove the fuel lines (have the drain pan handy and where safety goggles) - and then pop off the rubber mounts.
It much easier to replace the filter with the whole assembly on the bench. Not that it's that hard to do in the car, but if it's been neglected it will surely have some tight fasteners and dirt. It's VERY important to clean everything well before undoing the banjo nuts and other connections. Having it on the bench is more efficient and makes for easier cleaning and final inspection without laying on your back under the car.

Edited to add: I also used clamps on the fuel line from the tank, and the line to the engine to minimize spillage. Only the gas from the filter and I think some from the accumulator came out that way but I'm not sure how much more would have come out, if any, if I didn't clamp the lines.

[ps2cho]

Originally Posted by long-gone

but I'm not sure how much more would have come out, if any, if I didn't clamp the lines.

I had a couple oz, if that. Just leave the gas cap alone (assuming it still holds pressure) and it should be fine.

[long-gone]

BTW - if anyone elects to remove the whole assembly, it's VERY IMPORTANT to disconnect the battery cable! You definitely don't want any sparks down there when working on fuel system components!

[lkchris]

I wouldn't put the crush washers in the "if needed" category.

ALWAYS replace and NEVER reuse these. That's the design intent.

This applies to oil pan drain plug washer, too.

German cars are different than American cars.

[JohnM.]

Originally Posted by lkchris

I wouldn't put the crush washers in the "if needed" category.
.

I would tend to agree. Luckily I ordered some new ones with the filter. The old washers were indeed crushed, and the OD was noticeably larger than the new non-crushed washer.

[MARINE_V]

This is so freaky.. I just ordered this part and come on here to find out how to replace it..... Thanks for you post ps2cho, this will come in very handy...

[melliesplace]

Can you recommend the best fuel filter for my 1988 260e? I'm getting mixed messages from my web searches.

Also, any favorite sites or stores to buy from? I'm new at this, so any help is appreciated!

Melissa

[ps2cho]

Bosch only! Fastlane at this site sells them.

[melliesplace]

Thanks! I'll order it today.

Do you happen to know if the Bosch fuel filter also comes with the copper crush washers? Or where can I pick those up? My searches have all turned up empty. What size should I be looking for?

Thanks again! Much appreciated.

[atikovi]

Originally Posted by ps2cho

Crank the car, it may take 10-20secs of cranking for the filter to fill up.

Just turn the ignition on for a few seconds to energized the pump until it shuts off again. Do it 3 or 4 times and you won't have to crank it much.

I got a Mann filter for $17. Sanded the faces of the old washers until they were flat and reused them. Kinda cheap for the filter manufacturers not to include the washers. I mean, they put the plastic caps on the filters which probably cost just as much.

[tbomachines]

I need to interject here. I reused my old washers like an idiot when I repalced my FF. I now have a fuel leak...smells faintly like gas after the system pressurizes and has a tough time starting cold. It could be other factors but a tiny fuel leak/seepage is by far the prime suspect. Use new washers! I have to crawl under there again with 5 cents worth of crush washers

[TnBob]

For those working in close quarters, there are 4 fasteners holding the cover on.
One very visible as you first get under the car, two facing the rear on the engine side that are slightly angled and then on in the center rear down in the molded circle that on mine is angled about 40 degrees or so towards the axle.

A nice bright LED spot light sure is helpful too.