Mercedes W124 M103 Injectors Replacement

To start, we need to remove the air filter housing.

First, disconnect the air intake duct connection (blue triangle). Pull it out of the air filter housing and place it under it. Removing the air flow sensor is not necessary (right side of the duct).

The air filter housing is secured using 3 nuts. Using the 8mm socket, undo the nuts and store them safely. They are located: 1 on the bottom left, 1 on the upper left, one on the middle right side, under the housing (red triangles).

Next, disconnect the vacuum line from the top hose, then undo the hose clamp. Due to age, this step might be easier or harder, depending if it was replaced before. Holding the clamp undone with pliers, pull the air filter housing up until completely removed.

With the air housing removed, we now need to ensure that the work area is clean and free of debris. First, using quick cleaner or carb cleaner, clean the air intake port then cover it securely using a plastic bag with an elastic band, or a large nitrile glove. This will prevent debris or dust from entering the system.

Next, using air (air system, can, air blower, portable vacuum), clear the area around the KE-Jetronic module (red triangle), as well as the injector side. Use a long hard brush to remove any hardened surface dirt and don't forget to clear it using air.

Once the larger debris, dirt and dust has been cleared, spray down with quick cleaner to ensure the more stubborn dirt is removed, particularly around the injectors.

Using a shop towel or microfiber cloth together with quick cleaner, clean the dirt around and any residues around the injectors as best as possible. Wait for everything to dry, especially paying attention to the bumps on top of the intake which will pool liquid.

Next, we need to unbolt the wiring rail in order to gain easier access to the fuel distributor lines, as well as the injectors themselves.

While not necessary, with some additional work, you can remove the cover of the rail, undo the zip ties holding the wires together, and remove the rail completely while putting the wiring aside. This is however not necessary.

There are 3 bolts (red triangles) holding the line down, using the 8mm socket remove these and store them safely.

Once the bolts are removed, the rail will remain in position but allow for some movement.

We can now start removing the fuel lines.

Keep some tape handy to cover the open ports, this will prevent dirt and debris from entering the system.

Start by disconnecting the lines from the ends of the injectors (red triangles), there is a line for each injector (6 in total). In addition to this, you also need to remove the line to the cold start valve.

If the lines are too hard to undo, while keeping pressure on the wrench, lightly tap the wrench with a hammer. This will ease the process substantially as it will allow the connections to break free.

Next, we need to disconnect the fuel lines (blue triangles) from the KE-Jetronic module, the order is not important, however removing some first will allow for easier access to the others. Additionally, for better access, we need to remove the line to the Cold Start Valve, as well as one end of the line leading to the Fuel Pressure Regulator.

Once each line is removed, make sure to cover any open ports to ensure to dirt gets into the system.

Once the fuel lines are removed and the areas around the injectors are clean, we can start removing the brackets holding the injectors down.

The injectors are held in place by Allen head bolts. Be warned that these tend to be quite soft and easy to strip. To this extent, I recommend a set of new M6 12mm bolts at hand, to replace the old ones should they strip or warp during removal.

Using a ratchet wrench, as well as an Allen head, start removing the screws and brackets one by one. As with the fuel lines, light tapes on the wrench will help things along and prevent potentially stripping the bolt heads.

Once the brackets are removed, the injectors can be pulled out, together with the injector housing. The housing for the injectors is no longer available, so be careful when removing them.

With the injectors removed, use a cleaning cloth with quick cleaner to clean around the port, making sure to not introduce dirt intro the port.

We should now start preparing the new injectors for assembly.

First, remove the old gasket from the old injector mounting brackets and clean the brackets with a clean cloth as well together with either quick cleaner or a cleaning agent.

Mount the new O-rings on the injector housing.

Next, remove the output protective cap from the new injectors (small end).

Take the new injector seals, and first apply a bit of silicone grease to them. This will make installation easier.

Slide the new injectors into the new injector seals until flush with the top part.

Take the prepared injectors and place them in the housings, while keeping the top end protective cap on. This will save additional cleaning later, as well as potential dirt getting into the system.

Remove the protective tape from the injector ports and place the prepared injectors in one by one, while still keeping their protective cover on. During reinstallation, ensure the open part of the injector housing is oriented up, and ensure that the injectors themselves are aligned vertically (2 flat sides parallel on each side).

Give the mounting brackets a quick clean then one by one, place them over the injector top ends. The brackets needs to click in place, specifically grab the head of the injectors (yellow triangle).

To do this, you need to push down on the wide part of the bracket until an audible metallic click is heard at which point the bracket will be able to move freely around. An easier approach which spares your fingers is to use an open clipper to push down on these.

Next, secure the bracket using either the new or old bolts. Torque them tight as to ensure secure fitment (7Nm then another +90 degrees and one more +90 degrees).

If torque measurement is not possible, tighten down until there is no more movement possible (hand strength), with care as to not strip the bolt heads - they will warn you that you have gone too far. Once up to spec, they should not allow for further tightening.

With the injectors now in place, we can give the fuel lines a quick rinse.

To clean the fuel lines, first use a plastic brush together with a cleaning agent to remove dirt from the exterior, as well as from the threads.

Next, using quick cleaner or carb cleaner, place the nozzle at one end, and blow through the lines to ensure any potential contaminants are removed. Then, using compressed air, blow out the leftover substance.

Once completely dry, apply a bit of lithium grease to both ends of the lines. This will offer additional protection as well as provide some lubrication.

Next, place the fuel lines back. They will only go back one way, and it should be clear which goes where. Tighten slightly on both ends once aligned, but do not tighten them down completely, as to allow for a bit more room to work and in order to prevent cross threading.

Once they are in place, start by tightening down the ends on the KE-Jetronic system. Torque spec is 22 Nm, use common sense if you cannot measure, should be tight as to make a good seal.

If measurement is not possible, tighten down until there is no more movement possible (hand strength), with care as to not cause bends or other damage - they will warn you that you have gone too far. Once up to spec, they should not allow for further tightening.

Next, tighten down the ends at the injectors and the cold start valve.

Now is a good time to check for any leaks.

First, go through all the connectors again and ensure they are tightened, otherwise fuel will spray into the engine bay.

Once confirmed to be secure, reconnect the battery (if disconnected at the beginning) and attempt to start the engine. The system will need to regain fuel pressure, so a couple of cranks might be needed.

Check that there are no leaks. If leaks are present, shut off the engine immediately and tighten the connection, then retest.

If no leaks are present, proceed with the reinstallation of the wire rail and air filter housing, following the removal steps in reverse.

This guide is based on my experience changing the injectors in the parking rain, during a rainy week. As such, some pictures might be missing or are not that well documented.

In all instances, use best practices, and ensure adequate steps are taken to ensure your safety, as well as to ensure you do not damage any of the parts.

Changes, additions and general corrections are most welcome. Feel free to reach out.