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Autopapyrus · Mercedes-Benz S-Class 4.0 CDI V8 OM628 (2004)
https://autopapyrus.com/guides/mercedes-benz/s-class/fuel-injector-replacement/
Compiled automatically from service literature and owner experience. Specs are for the typical configuration — check them against your exact car before you start.

Mercedes-Benz S-Class 4.0 CDI V8 OM628 (2004): Fuel Injector Replacement

OM628 (Bosch CP1) injectors are known for seal leaks and wear. Symptoms: hard starting, smoke, rough running, a rising oil level with a diesel fuel smell. The job requires cleanliness and care. The most common mistakes are seized injectors that break when pulled out, and dirt getting into open fuel lines.

Difficulty: Hard Time: 6-10 hours (all 8 injectors), 3-5 hours per cylinder bank Steps: 14 Tools: Socket set and ratchet, low-range torque wrench (for the injector clamp and fuel line flare nuts), open-end or flare-nut wrenches for the fuel line nuts, injector puller (slide hammer with adapter), injector seat cleaning kit, syringe or bulb for removing fuel, caps/plugs for open fuel lines, clean rags and brake cleaner, Mercedes scan tool (Star/Xentry or equivalent) for checking codes and adaptation

Part

  • 🔩 Bosch common rail injector for the OM628, Bosch 0445110208 (cross-reference A 628 070 05 87). You need 8. If you use new OE or remanufactured injectors, match the same part numbers on both banks. Kit per injector: copper sealing washer under the injector body, hold-down clamp, O-rings, and fuel line nuts as needed. Valve cover gaskets as needed based on condition
There's a full repair manual for this car Every system, wiring diagrams and torque specs — not just this job. Haynes and 7 more. See manuals →

Step by step

14 steps
  1. Before starting, read the fault codes with a scan tool and check the oil level and smell. If the oil is diluted with fuel, change the oil and filter after replacing the injectors.
  2. Disconnect the negative battery terminal. Relieve the residual pressure in the fuel rail: wait at least 10-15 minutes after shutting off the engine and do not start the engine.
  3. Remove the plastic engine covers and the air ducts. The engine is a V-type, so to reach the injectors on both sides you will need to remove the air ducts, the air filter with its housing, and any wiring harnesses in the way.
  4. Thoroughly clean the engine around the injectors, fuel lines and valve covers with compressed air and cleaner. No dirt may get into the fuel system.
  5. Disconnect the injector electrical connectors. Remember or label the routing of the harnesses and the locations of the retainers.
  6. Unscrew the flare nuts of the high-pressure fuel lines from the rail and the injectors. Hold the fittings with a second wrench and do not bend the lines. Immediately cap the open fittings. Do not reuse high-pressure lines if the cone (sealing seat) is deformed.
  7. Remove the injector return line (leak-off line) and remove the valve cover or any other access cover if the injectors are located under it. Replace the cover gaskets.
  8. Remove the bolt and take off the injector hold-down clamp. Carefully pull the injector out of the cylinder head, working it back and forth along its axis. If the injector is seized, use a puller with a gentle, steady pull rather than a pry bar, and treat it with penetrating oil first. Hard blows are not acceptable.
  9. Make sure the old copper washer came out with the injector. If the washer stayed in the seat, remove it with a special tool. Clean the injector seat with a dedicated brush or scraper without letting carbon fall deeper into the cylinder, then wipe it dry.
  10. Install a new washer and the new injector. Insert the injector straight, without tilting, and do not seat it on top of carbon deposits. Install the clamp and tighten the mounting bolt evenly. Use the torque specified by the manufacturer for your engine. Do not exceed it, or you may deform the injector.
  11. Install the high-pressure lines. First thread the nuts on by hand without tension to avoid cross-threading, then tighten them with a torque wrench to the specified torque. Connect the return line and the electrical connectors.
  12. Reassemble everything in reverse order: valve covers with new gaskets, ducts, covers. Reconnect the battery.
  13. Prime the fuel system: turn the ignition on for a few seconds several times, and if necessary use the manual priming pump or bulb. Check for leaks at the connections before starting.
  14. Start the engine, let it idle, and inspect the connections for fuel leaks. Read the fault codes with the scan tool and, if needed, perform adaptation or coding of the new injectors if your equipment requires it. Check the oil level after driving.

Common mistakes and warnings

  • The common rail fuel system operates at very high pressure. Do not open the lines with the engine running or just after it has been shut off, because a fuel jet can penetrate the skin. Do not touch the injectors and lines while the engine is running, and do not check for leaks with your hand. If you lack experience, special tools and a scan tool, have the work done at a repair shop. Seized injectors are easy to break off, and then they must be pressed out of the head, with the risk of damaging the cylinder head itself.