How to re-haul the rear fuel delivery system on w123 (gasoline)

The fuel delivery system on w123 consists the fuel tank and a collection of components until it reaches the combustion chamber. This article will focus on the rear components until it reaches the CIS fuel injector assembly. The CIS system is pretty much a black box for me still. I will however go through how you change the fuel injectors and gaskets in another article.

I had to do a re-haul of the entire rear fuel delivery system when an entire tank worth of gasoline (~80 liters) had leaked out after my 280CE was parked for a while, totally delayed my plans for cruising in the summer by almost a week. This made me furious and is the reason for why I wrote this article.

Preparations

It is up to you how many part you want to change. I would recommend to change all the rubber fuel hoses and fuel filters as a minimum!

Parts

  • New fuel tank filter (the first one)
  • New main fuel tank delivery hose
  • New fuel delivery filter (the second one)
  • New high pressure flexible fuel hose
  • Two other fuel hoses and clamps (see pics)
  • 4 fuel assembly rubber mounts
  • [New fuel accumulator?]
  • [New electric fuel pump?]

Tools

  • Spanners
  • 45mm socket
  • screwdriwer
Common questions

So why bother changing the fuel accumulator? Well it can lead to problems such as warm start problems (yeah the M110 usually have warm start problems more than cold starts), this is due to the inability to hold fuel pressure after shutting down the engine and starting it before it gets cold. There are separate start up procedures either if engine is cold or warm. I thought a broken fuel accumulator was the problem with my car’s warm start problems, but it was in fact the old injectors and brittle gaskets that was the cause since they could not maintain fuel pressure.

Why bother changing the electric fuel pump? This has to be the number one reason why people are stranded in their cars with M110 engine. After some time (around 7 years if in daily use) it will with certainty stop working. The part is however quite expensive and I would suggest to not change it if is still working and not obviously very old. A maintenance tip instead of investing in a new part is to remove the corrosion on the electrical connections.

Procedure

Pretty straight forward, just change all the fuel hoses and refit… OK I will guide you through it like Gandalf in the mines of Moria. Smelling fuel is usually an indication of leaking hoses.

Before you even start you have to disconnect the battery to avoid explosions. Then completely drain the tank, either by sucking up the fuel from the gas filler tube or by unloosening the main tank outlet hose from under the tank. I would suggest you drive the car nearly empty before undertaking this task. Make sure the area you are working in is very well ventilated since gasoline fume is highly explosive!

Main fuel hose 280CE

After the tank is drained you can remove the plastic cover start by removing the thick fuel hose connected to the tank. Just have a look at this one in the picture under which caused all the fuel in my car to drain out.

broken fuel hose
Broken main fuel hose

A massive 45mm socket is needed to remove and fit the fuel tank filter. Remember to replace the gasket as well.

fuel tank filter 280CE
Fuel tank filter.

Now you can remove the flexible hoses connecting the high pressure and the return hard lines. If you see rust on the connection then you have to be extremely careful not to round off the relatively soft metal on the hard line unless you want to go through with replacing the entire line. Believe me this is a shit job (my old hard lines were rusted and leaked fuel).

High pressure fuel line W123
High pressure hose

Disconnect the two electrical wires to the fuel pump and when all the fuel lines are disconnected from the body, you can go on and loosen the 4 bolts holding the bracket for the pump, fuel filter and accumulator. Beware this bracket can be pretty rusted and you need either to get hold of a new one or remove the rust and repaint the one you have. The rubber mount bushings are probably dried up or broken so you should replace all 4 of them.

On a work bench you can now go on with the job of replacing the components and the old fuel hoses. Look at the picture below on comparing new and old hoses.

fuel assembly hoses 280ce
Old vs new fuel assembly hoses.

Assembly is just opposite of removing. The main thing you have to consider is to make sure there are not any leaks before you start driving. Look at the picture below to see how the components should fit together in the assembly.

Fuel pump assembly 280CE
Fuel pump assembly 280CE. From top to bottom: Fuel accumulator, fuel filter, fuel pump.

The best thing is that there is no need of special fuel bleeding or start up procedure when starting up the car after fitting all the lines together. Just refill the tank and crank the engine and it will start right up. Nothing difficult as with the diesel.

Then mount the assembly and fasten the hose to the fuel filter. Don’t forget to fit the electrical wires to the fuel pump and mount check for leaks when starting the car. When no leaks are detected, mount back the plastic mud cover to protect the components. Hopefully you will have no leaky days or being stranded by a malfunctioning fuel pump.

Cheers!

Finishing the “Restoration”

The restoration battle has been won
Me 1 – Car 0

The car is welded, put together again and finished! Who would believe that? I am super proud of my own work. I managed to strip downm weld and then assemble the car on a tight schedule. In the process I learned how to weld body panels. I in fact learned so much through this project that I know tons of new stuff about W123s.  This job was the inspiration to create this very site.

The project included the tricky disassembly of the whole rear sub frame and drive train with following refurbish. This has been almost two years of work, although with large gaps between quite intensive working periods.

Which areas did I end up welding? I couldn’t cover all of them in the blog.

Sounds like a lot, the issue was that it had many places with small holes, and with welding the job is just as long when it involves small or large areas. You still have to remove old metal, remove paint and body protector coating, maybe interior parts, cut out new metal piece and shape it, weld it in place, grind it, polish it and paint it. Same process over and over again.

What mechanical areas did I fix? The car was from before very mechanical sound and basically I just replaced rubber wearing parts.

  • New flex disks for drive-shaft
  • New center bearing and hanger for drive-shaft
  • New upper control arms and sway bar bushings at the front suspension
  • New shock absorbers, Bilstein original extra stiff for flatter cornering
  • New fuel hard lines and rubber hoses
  • New sway bar bushings and links rear
  • New subframe rubber mounts
  • New brake rotors and pads
mercedes benz 280ce front without bumpers
Without bumpers and needing some paint
mercedes benz 280ce rear without bimpers
Rear Facing

Basically all the lower sides and front needs repaint, these are areas not so visible, none the less I got some paint with the right color code (172).

right front corner before respray
Right front corner
left front corner before respray
Left front corner – red base paint
Respraying lower front and sides
Respraying with second base paint layer
Respraying side
Painting continues
leather interior w123 280CE
Assembling the leather interior again

So what is the result? Well a car that looks really good and drives like like a new Mercedes. Super smooth and fast!

It went from looking like this in (2012):

Stripped 280CE front
Stripped car

And one year after (2013):

Mercedes 280Ce and 300TD
The product of lots of work and dedication

Welding the Front Quarter Fenders

Why get new ones when you can use 30hours trying to fix the old ones?!?!

I wanted to weld the front fenders rather than replacing them, even though I have two replacement fenders. Why is that?

  • Welding practice
  • Stubborned idiot like myself
  • Keeping the car more original
  • No need for respraying fenders since the other ones are blue
  • Replacement fenders have hole for antenna, and my antenna is in the trunk

So I got on with that, but I might replace them in the future if I’m not satisfied with the result.

rusted front fender
Front fender rusted in the seam, like on every w123. The other one is the same..

So on to the cutting, and trying to recreate the corner, was quite painfully difficult actually.

comparing the fenders
Comparing a rust free fender with the old for reference

So then I welded and this was the result:

Front fender welded
After the welding…

It looks better than it was, turned out when i fit it on the car I needed to do a massive job with the filler, but after the result was quite nice. Good enough for now, might change the fenders in the future when doing a complete respray though, but then I will get completely new ones without old paint and stupid holes for antennas.