PeachParts Mercedes-Benz Forum - Fuel leak fix described in detail

Well, this leak is finally fixed, had to smell diesel and see leaks on my driveway for about 2 weeks. It was getting pretty bad toward the end, a nice puddle under the car the night before I did the repair.

Maybe true, the worst part of this job was looking at it, trying to figure it out, then finding out you needed special tools to do it. See pictures on the "DIY" section from the homepage. View photos of all this on the DIY section.

For those who have yet to do this "simple" job, here are the steps, as I remember them, and this was on my 1991 300d 2.5 engine, the leak started with 90k on the engine. I've heard other model years of the W124 might be a bit different. My leak was at the injector pump and the problem is the delivery valve O-ring seals.

1) You'll need a T30 torx wrench.
2) You'll need the splined socket for your 1/2" socket drive. Cost $45 or so, then you can resell when done.
3) Torque wrench. You'll need to torque the valves as such, but I don't know why they say torque then loosen, but here's what is says:

Torque to 30 Nm and loosen
Torque to 30 Nm and loosen
Torque to 30 Nm and then an additional 5 Nm.

4) You need 5 rubber washers. The copper washers, as someone else said and so far, you don't need to replace. Cost of the rubber washers, maybe $3 for all 5.
5) A 14mm short handled open box wrench to fit over the 1/2" tall copper nuts at both ends of the injector lines.
6) If you're a mechanic-lite like me, you might want to take digital photos left, right, and top of the whole area so when you put it back together, you can see on computer screen what clip went where, how high the STOP lever was, and which Torx collar goes on top of which.
7) You'll need a 6mm ? wrench to take off the STOP lever.

Clean the area well. You don't want debris of ANY kind going into the injector area. Get rid of any loose debris upper and lower for that area, especially since you'll be leaning over that area while doing the repair.

Basically all you're going to do is loosen and remove the fuel lines, get them out of the way by moving them back, then remove the delivery valves which are sort of like a spark plug, and change the O-rings.

As far as staring doing the job, I did mine in a series of wrong steps, so I'm not sure which area to start in first, and maybe there is no right area to start in, but basically, there are 4 areas to work on. You have 1) the lines at the
IP (injector pump) 2) the lines at the injectors themselves, and (3+4) the two separate brackets that hold them in place so they don't shake.

I don't know if the brackets should be taken off first or not, but if I had this to do over again, I think I would start there. You'll see the first bracket holding the first set of 3 lines easily. It's on the manifold, you need a 10mm wrench to get those 2 bolts off. The 2nd bracket, holding the other 2 lines, is not easy to find. Looking from the top of the engine down, it's view is sort of occluded by a small dark plastic coated cable of some type that runs from the mess of wires in front of it, all the way back to near the center of engine compartment. You have to get rid of that line in order to get the bolt off so you can get the 2nd set of injector lines out.

To get that line out of the way, you have to loosen (but not take off) the cruise control module (?). I'm not sure what the name of the part is, but for now, let's call it the cruise control module. It's sort of square, maybe 3" x 3" as you're looking down at it, and held on by 4 bolts. The upper right bolt of that module will have to be removed, the other 3 loosened pretty well, but not all the way. Once that's done, you can lift that black plastic coated line out a bit, enough to get a 10mm socket onto the bolt under it, and unscrew the injector bracket holding the 2 lines together. (Putting that injector bracket back is a real hassle, so look at the bracket once loose, and see how the clip inside the bracket slides back and forth. It is this annoying clip that the bolt must go through when reassembling).

Once the brackets are loose, now loosen both ends of all 5 injector lines with the 14mm short box wrench. Once loose, work the lines so they go back and out of the way.

Draw a picture of how the Torx collars are, of which overlaps which. Holding the Torx socket very upright, being careful not to strip them. They're on very tight for such the small, star shaped bolt that they are. If by chance they strip, you'll have to carefully use a small vice grip wrench on them, preferably in the upright position so as not to torque them sideways. Careful not to get any debris in the injector pump! Once loose they come up easily. There's an annoying brown plastic line right in the way of all this, coming from the fuel filter. I don't know if this could be taken out; I left mine alone so it'd be less potential problems, but it's reeeeeealy annoying working around it.

Note or mark how high the STOP lever is so you put it back at the right level when reinstalling. Take the STOP lever off. It uses maybe a 6mm wrench at bottom, be careful when it comes loose so as not to lose the nut and tiny washer.

Take the flat Torx collars off, then use the splined socket on the fuel delivery valves. Some on the forums said they just loosened the valves a bit and used a pick to get the O-ring seals out. I tried that, but it was a waste of time for me. Doing this also runs the risk of getting debris in that area. Much simpler to take the valve completely out. They're simple, but when you do, just be prepared, as a spring will come out the bottom. So go slowly, once loose, take them out at as sharp an angle as you can, then horizontal when you can, to prevent losing the spring. Once the valve is out and in your hand to inspect, dump the spring out so you can see how loose it is so the other 4 will go easier. Take the old o-ring off by hand. Lightly lube the new o-ring in some fuel, and put it on. The threads of the valve might have some debris on them, use a paper towel to clean that off so it goes back in better.

Once the valve is ready to install, take the spring and place it by hand, directly in the center of where it will go on the injector pump. Then place the valve directly vertical over it, lower and screw it down. Do that for all 5, then tighten with the splined socket to the specs:

Torque to 30 Nm and loosen
Torque to 30 Nm and loosen
Torque to 30 Nm and then an additional 5 Nm.

Reassemble, remember to replace any injector line clips along the way you may have taken off, or that may have come off inadvertently. The clips are to prevent the lines from clacking together and breaking so if yours are cracked or broken, go get some. Put the lines at the injector pump on as tight as they were, but leave the ones at the injectors only hand tight for now. Put the STOP lever back on, and if you're like me, you'll lose time if you drop the tiny nut or washer.

At this point, everything should be back to where it was, with the exception of the lines at the injector pump just hand tight. If so, crank the car, will probably take 45 seconds of cranking, to get fuel to come out of the lines. When fuel comes out, tighten the lines at the injectors completely, and you're done!!

Start the car and look for any leaks, which unless you did something really stupid, there shouldn't be any leaks. If there is a leak, find and fix. If no leaks, you should be good to go. The car might sound a bit funny at first, but after a few miles, any additional clacking should go away, if not, you might have air in the line. To get air out, start the car, and SLIGHTLY back off one injector line at the injector (not at the pump). The car will buckle a bit like you're pulling a spark plug off a gas car, once it does that, tighten and go onto the next one until the problem is fixed.

Take it out for a test spin, and if all is well, sing praises to me.