Changing fuel filter
 

How hard is this to do, and are there any special tools required?

In other cars I've done this to it was a simple case of taking it out from the engine bay, but I noticed in the 124 it's under the rear side of the car for some reason

It's been "under the rear side of the car" on German cars for decades.

If it's like my model, there are no special tools required beyond the 1/4" drive extension needed for the socket to remove the plastic cover under the car.

I think you'll just need a couple rather large open-end wrenches. I believe you'll need a 22mm, 21mm, and then I think the other side will be the normal sizes, 17mm, 19mm, in that range. But nothing really special, other than the wrench sizes on the banjo fitting being a bit large.

Is there anything needed there to stop fuel leaking out?
Pressure release?
Clamps etc?

Or is it as simple as unbolt and bolt?

You won't lose a terrible amount of fuel, mostly a portion of what's in the filter and some pressure leak. You can loosen then retighten the fuel cap, which will help if there is any pressure in the tank.
There were a few variations from model to model, but I don't believe yours used any clamps. If so I would reuse them, MB uses excellent hardware. You will need to loosen the screws on the strap on each side of the filter, usually not a problem. You'll need a couple copper washers for the banjo fitting. You wil get a small amount of fuel when you loosen the first fitting, due to pressure in the lines. Protect your eyes at all times and wear ratty clothing.
HTH
Gilly

PS I usually loosen the strap that holds the filter in place FIRST, so it is ready to be removed once the hoses are off. You will need 2 wrenches when removing or installing the hoses/pipes to the filter, one for the fastener and one to counterhold on the filter side.

you will absolutely need a couple of the small aluminum washers that go between the fittings and the filter. These always leak if you try to reuse them.

DG

Thanks guys I'll go to the local MB and pick up the stuff I need

The rings should be copper though, not aluminum. See what the dealers sells you.

Just did my filer on a 91 560 SEL. I had to re-use my rings. they were copper and needed a good tightening to prevent leaking.

On the other end I used some teflon tape on the threads. I had an issue though. The filter came with a fitting that I had to remove because the one on the fuel line on the driver's side was fused/rusted onto the fitting. So when I removed the filter, that fitting stayed.

So I removed the bolt-but thingy on the passenger side with the TWO copper rings. I think unthreaded the filter from the line on the driver side. Not that I did it, I am sure next time will take a lot less than an hour!

If you anneal the washers with a Bernz-O-Matic then sand them on a flat piece of glass and fine sandpaper you should be able to reuse them just fine, but that's a lot of trouble so just get some new ones and be done with it. Damned if I could find any when I replaced the fuel filters on my car though.

The other thing I was thinking of doing along with the fuel filter change is removing the injectors and having them ultrasonically cleaned.
Does this seem like a good idea?
And, any write up on how to do this?
As far as I can recall, the last time I removed injectors on a car it was fairly simple, with the only thing to note was to put some grease around the rubber o-ring to make sure no fuel comes out.
Can anyone comment?

I replaced the check valve in mine also while i had pressure off the system since its right there.

NO leave your injectors alone.

It's not a good idea to get them cleaned??

What's the check valve?

you know we have owned 5 124's and i've never changed a fuel filter.... i think i have one in my parts bin... just haven't seen the need....

am i lucky, stupid or what?

To be honest in other cars I own (Japanese) the fuel filter is scheduled every 20,000km or so I think

Spetz, I've cleaned injectors before. But I have access to an ultrasonic cleaner and a variable voltage supply. If you don't have either, the injectors should be sent out for professional cleaning.

In general if you are using good quality fuel, the removing the injectors and having them cleaned is a bit over-the-top in my book. Are you trying to fix some sort of condition by doing this? Yes the filter should be replaced as scheduled, it should be at or around every 60,000 miles. If you have no problems but want to do "something", then just put a can of Techron in it every few months, but even then I think it's a waste of time. Just not tormenting the engine as much.....

The car has 62,000 miles on it, and basically I want to completely restore it. It's in pristine condition (bought new by my dad) and the only signs of wear on it is the suspension. Body and interior look brand new.
So, as part of the restoration I would like to do everything I can to get the engine driving like new as well. I was planning on injector clean as well as a carbon clean. I've recently added new engine mounts as well.

My local garage ultrasonically cleans injectors, so I would just take them out, get them cleaned/flow tested there and put them back in.

I can see you have yourself convinced this is somehow a good idea, so just, y'know, "carry on".

If there is a reason why I shouldn't, then I won't.
I just assumed that cleaner injectors would spay fuel better which would burn better

To turn your first sentence around a little, there should be a reason for doing this. "If there is a reason why you should, then you should". If it is running fine, then I'd just keep doing the basic maintenance and if you really want to try something to keep the injectors clean, then be picky about where you buy fuel and you can add some Techron cleaner to the fuel once in awhile.

I think you are right about the second sentence, but if the engine is running fine, better can become the enemy of best.

Gilly

Actually there is somewhat of a humming vibration from the car at certain rpms. I am not sure whether it is normal or not, but I have this feeling it's not.
It's quite weird, because the humming vibration comes and goes. For instance, it's present at 1,500rpm, 4,000 rpm, 5,000rpm and maybe some other particular revs.
The vibrations are very slight, and not noticable, and there are no vibrations when I let go of the throttle.

Techron I assume is a particular brand of fuel system cleaner fluid?

Spetz, sounds like your 1994 E220 experiences a "harmonic vibration" at certain engine rpm's or car speed. Could be due to the driveshaft being slightly out of balance, or other things.

Gas sold at Mobil stations in the United States has Techron in it. You can also buy Techron in small plastic bottles and add it to a full tank of gas to clean injectors. Many folks recommend adding Techron to a tank of gas immediately before a scheduled oil change, thinking that it may contaminate the oil slightly.

Bad spray patterns in small amounts would cause an uneven idle or a slight miss. The worse the spray pattern the more evident it becomes/the worse it gets.
Gilly

There is a slight miss. I originally thought it was spark plugs but I checked my service log and they were changed some 1,500 miles ago (almost 2 years ago).
The leads haven't been changed, but they are covered and I cannot see their condition. At 62,000 miles, would they need replacing?

Ferdman, the vibrations are totally rpm dependent and have nothing to do with speed. Any ideas what it can be from the engine?

looks like enough said about the fuel filter replacement,its easy,loosen up the bracket that holds it tight,the open hood,loosen up fuel pressure line going to the cold start valve,this best releases built up pressure,so you dont get sprayed in the face,wrap a good rag around the fitting under hood then loosen it till no more fuel comes out.then perform the other described tasks,remember to replace the copper washers,these are the seals or gaskets,if there not new or 100% flat you will have high pressure leaks,leave the in jectors alone,a good bg high pressure flush works great,i generally as a rule of thumb run injector cleaner every other tank,mits made from lucase oil racing products,it works wonders.good luck.oh and while your under there loosen up and replace both check valves if you have 2 fuel pumps,there coming off the fuel pump end,where the main fuel line comes from,also replace the copper washers here to,good luck.

If the car has only gone 1500 miles in the last 2 years, it'll probably run better if you take it out on a long drive with some techron in the gas, The gas itself might even be kind of old (or lower octane), which could also cause a slight miss. Something tells me if I said poor spray patterns cause orange tinted exhaust that smells slightly like papya, you would tell me your exhaust is turning slightly orange and yes it does smell a little like papya now that I mention it.

You might also check to see if the proper plugs were installed and also for proper gap. The wires should still be good, you'd have to check resistance or get it on a scope to see for sure.

The plugs were installed by an independent Mercedes mechanic. He's always used OEM parts for all the work I had done to it so I have no reason to think that the plugs are wrong.

The car gets driven rarely, but each drive is fairly long. Usually at the very least 30-50 miles each time, and at times I may drive it up to 150-200 miles in one go.
I believe the gas in it is no more than 3 months old to my memory. Usually 98 octane, and at worst 95 will go in.

Exhaust smells and looks fine. However I noticed after driving it a while in hot conditions I hear the fuel pump whizzing louder than usual.

When attaching the fuel line to the filter, apply a little bit of grease on the mating surfaces.

Rob