Mercedes E Class W124 ignition coil

Typically, when the component breaks down, the following symptoms occur:

• The engine works unstable, especially in cold weather.
• A strong burnt smell comes from the component.
• The “Check Engine” dashboard indicator is on.
• Engine power significantly reduces after pressing the accelerator pedal.
• Fuel consumption increases.
• The engine starts heavily and stalls during driving.
• The engine vibrates during idling.
• Black smoke with a fuel smell comes from the exhaust pipe.

All these symptoms can also indicate malfunctioning of other parts, such as high-voltage cables and others. Examine the whole ignition system if you notice these symptoms.

First, inspect the component. It shouldn’t have cracks, dents, black spots and other defects. After this, check the correctness of wires connection using a diagram from the vehicle’s service and repair manual.

Next, measure the winding resistance by connecting the probes of a multimeter to the respective terminals. Remember to refer to the car workshop manual, as nominal values for an ignition coil can be different for various car models. Typically, on most cars, the primary winding has standard resistance measurements within the range of 0,5–3,5 Ohm, and the secondary winding should have 5–16 kOhm.

For thorough diagnostics, an oscillograph is necessary. That is why it is better to visit a car workshop if you fail to detect the problem yourself.

Carefully read the vehicle’s service and repair manual before the replacement. You will need:

• spanners of proper sizes to unscrew fasteners;
• an ignition coil removal tool;
• electrical contact grease;
• a clean cloth to wipe dirt;
• a torque wrench to tighten fasteners.

The replacement algorithm:

1. Shut down the engine and wait till it cools down.
2. Disconnect the negative terminal from the battery.
3. Remove the plastic cover protecting the part.
4. Take a photo or mark the cable connection.
5. Disconnect the cables from the component.
6. Unscrew the fasteners and remove the part.
7. Clean its mounting location from dirt.
8. Apply a special grease to the part’s connector.
9. Install the new part and tighten its fasteners with a torque recommended by the vehicle manufacturer.
10. Connect the cables using the photo you’ve taken earlier or follow the markings.
11. Connect the battery negative terminal.
12. Make sure that the part works properly.