The problem of misfiring ignitions on the BMW 6 – how to fix it?

BMW driver’s question

On a cold engine the ignition drops out on the first, second, third and fourth cylinders. When the car is warmed up, it works properly. My suspicion of the cause of the problem falls on the eccentric shaft from Valvetronica. I know that they like to jam. How can this hypothesis be confirmed? Could other components be the cause of the ignition loss?

The problem was on a BMW 6 E63 with the N62 engine, but it may also occur on other models.

BM Cars service response

The problem of misfiring in any engine is a very complex problem. In the case of the N62 engine, due to its elaborate design, this phenomenon can be caused by very different faults.

The most common faults are in the ignition and injection systems. In the ignition system, attention should be paid to the frequency of spark plug replacement and the inspection and possible replacement of ignition coils. Particular attention should be paid to the proper selection of spark plugs (according to the BMW catalog) and the uniform selection of ignition coils (the same manufacturer and model).

In the fuel injection system, after relatively short runs, fuel injectors are damaged, which can cause ignition loss at first. After a longer period of operation, engine damage can occur (piston burnout, cylinder head damage, seizure).

In addition, an additional reason for ignition loss can also be a mechanical problem with the engine. Under the influence of various factors including, for example, damaged injectors – there is a reduction in compression on individual cylinders. This causes the effect of ignition loss at first and later also problems with starting a cold engine.

Occasionally there is damage to the eccentric shafts in the Valvetronic system or damage to the Valvetronic motors themselves. The result is underclosed valves or a lack of synchronization of closing and opening. This fault is particularly difficult to diagnose. Measuring the dislocation of eccentric shafts is very difficult and expensive.

The engine controller also remains as the final component responsible for engine operation. Failure of this component is rare, usually associated with its unsealing and access of moisture, or unsuccessful attempts to repair it, or to overclock performance (chip).

Suggested car repair steps

In summary, we suggest the following repair plan:

1. Full computer diagnostics of the engine with particular emphasis on checking the injection and ignition system.
2. Physical inspection of the condition of the spark plug coils.
3. Engine compression measurement with oil test.
4. Verification of fuel injectors (on a measuring table).
5. Verification of the condition of the engine controller installation and the controller itself.
6. Verification of the Valvetronic system along with measurement of the eccentric shafts.

After performing the above steps, it should be possible to make an accurate diagnosis and determine the cost of a possible repair.

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