The injector hard lines deliver fuel from the injection pump to the injectors are very high pressures; well over 1000 psi! The smallest hair line crack in the metal line will lead to fuel leaks. In such a situation they will need to be replaced.

Beyond that, not much goes wrong with the hard lines, but it's good to learn how to remove and install the lines so you can pull them off to more easily do other jobs like replacing your glow plugs.



  1. Mercedes W123 Fuel Injector Hard Line Replacement, Fuel Injector Hard Line: step 1, image 1 of 1
    • Begin by marking the hard lines. Each one goes in only one location, it will make it easier to re-install the lines or to install your new lines if you mark where each shaped line goes on the injection pump/injectors.

  2. Mercedes W123 Fuel Injector Hard Line Replacement: step 2, image 1 of 2 Mercedes W123 Fuel Injector Hard Line Replacement: step 2, image 2 of 2
    • Then begin removing the clamps that hold adjacent hard lines together.

    • You'll use a 8mm socket on top of the bolt that holds the clamps together, and a 8mm box end wrench on the bottom nut that the bolt goes in to.

    • Go slowly with this and be careful to not drop the nuts or clamp pieces as they can fall behind the injection pump. It's not impossible to get them out, but it can be difficult.

    • The second picture shows the hard lines with all of the clamps removed. Be sure to re-install all of the clamps on the lines; they help prevent the lines from vibrating excessively. The vibration is what tends to cause them to crack!

    You do not have to take apart the clamp. Loosen the bolt and nut and slip the whole clamp off. Replace the same way. Again DO NOT completely disassemble the clamp.

    James Scanlan - crwdns2853112:0crwdne2853112:0

  3. Mercedes W123 Fuel Injector Hard Line Replacement: step 3, image 1 of 2 Mercedes W123 Fuel Injector Hard Line Replacement: step 3, image 2 of 2
    • Now, use a 17mm wrench loosen the rear-most nuts on the hard lines at the injection pump.

    • Then, use the same wrench to loosen the nut on the same hard line at its respective injector.

  4. Mercedes W123 Fuel Injector Hard Line Replacement: step 4, image 1 of 1
    • You can then remove that hard line.

    • Proceed in the same manner for the other lines until all are removed.

  5. Mercedes W123 Fuel Injector Hard Line Replacement: step 5, image 1 of 1
    • While your hard lines are off, cover the hard line fittings on the pump as well as at each injector to prevent contamination from entering. The injector nozzles have very small openings that can be easily clogged.


To reassemble your device, follow these instructions in reverse order.


Nicolas Siemsen


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Excelente Guia Muchas gracias!!!

Pippenpy - crwdns2853112:0crwdne2853112:0

do you need to bleed the lines after you put them back on?

john umbanhowar - crwdns2853112:0crwdne2853112:0



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