In many of the entries, I have mentioned a permanent vibration in idle (it can be felt even inside the car), caused by the injector problems. This time – about more exotic cases.

What would you say regarding the following situation (the vehicles are equipped with N43/N53 series engine, but the problem can be present also for other engine sets):

a. ../F5/F7 indicates correct mechanical efficiency of cylinders in idle;

b. if the engine uses Stratified charge ../F5/Shift+F6/F5 also indicates correct values, they slightly change – DME tries to find a perfect idle step by step;

c. all other parameters of the injectors are in the allowed ranges. 

But the vibration in idle can be strongly felt inside the car!

Without illusions – a typical service center would recommend replacing the injectors, spark plugs, ignition coils, then – Lambda probes, etc. But – DME itself thinks that the engine runs perfectly! How so?

As I have seen at least 3 vehicles with such a problem and an identical cause of this problem, I thought – it is worth describing it. What to do in such a situation?

Usually, I start the check-up by opening the engine hood. Placing the hand on the decorative cover of the engine makes it easy to make sure if the engine itself is vibrating. Why it is worth to make sure about it once again? In theory, the camshaft sensor can be incorrectly re-adapted (or even replaced) or some other, quite exotic problems (about this a bit later), which lets the DME think that the engine runs perfectly, but it actually vibrates. 

So – in all (more than three) cases, the engine works very evenly. 

Next step – place the foot on the exhaust (on its nozzle). Of you feel a strong vibration – it’s worth checking further. In all cases – when placing the foot on the exhaust, it was vibrating very strongly. In all problem situations, the cars’ exhaust was modified – they have “sports” mufflers of different manufacturers installed. 

Why such situations arise? 

It has to be understood that N43/N53 series engines are particular. They can work in two fundamentally different injection modes (Homogeneous injection mode and Stratified charge) in idle. They have increased compression (1:12). Their exhaust is equipped with a specific NOx catalytic converter. To make the situation even more complicated, these engines on the go can also use Homogeneous lean mode (in the range of medium power, or if in the Stratified charge mode an increased density of the misfires is noticed) in addition to the two modes mentioned previously; also the desulfation of the NOx catalytic converter can be performed. While driving – 1x .. 3x in a minute, the NOx catalytic converter regeneration is performed. These engines work in very different and specific injection modes! It is clear that the tuning companies have not done in-depth research and haven’t developed the exhaust mufflers exactly for these engines’ specifics. The customers themselves often adjust similar engine mufflers to their N43/N53 if the aftermarket companies do not offer the mufflers intended exactly for N43/N53series engines. For example, the versions of the popular N52 and N46 engines. The result – unfortunately, unpredictable. The result may be very satisfying, but there are times (and many times) that the exhaust gets more “bassy” or even the exhaust, and all cars start to vibrate!

The OEM exhausts of nowadays BMW are very complicated!

Pay attention to the part marked in the image (E60; 530i; N53):

This resonant oscillation damper muffles undesirable vibrations of the exhaust in the exact frequency (RPM range). Typically, there are several such dampers in the BMW exhaust, but their number (for example, for diesel engines) can reach 7 .. 8 pcs! Each of these dampers is unique – with a specific mass; mass center; rubber – with a correctly chosen hardness. The vibration muffling functions are also performed by the precisely placed elastic fastening elements; the appropriate construction of the muffling elements (shape, the internal structure of the element, etc.), and corrugated connections (popular for the diesel engines). In its labs, BMW AG has tested and developed to excellence the exact exhaust tract and adapted it to the exact vehicle and exact engine. Have you seen such resonance mufflers in the aftermarket “sport” exhausts? I haven’t seen any.
My recommendation – if you choose an aftermarket exhaust system, be ready for certain surprises. A strong vibration will appear; it is possible that you will not pass the TI because the allowed noise level will be exceeded.

What can cause such a strong permanent vibration?

If you feel the permanent vibration when touching the decorative cover of the engine, possible causes:

a. damaged engine and/or gearbox mounts – “pillows”;

b. some of the aggregates (for example AC compressor, alternator, power steering pump) is mechanically damaged – it creates increased and variable load to the engine. If necessary, you can take off the V-belt for a short moment and evaluate the performance of the engine without the lead of these aggregates;

c. as I already mentioned at the beginning of this entry – the cause of the problem can be anything connected to the camshaft sensor and the tooth ring to the camshaft itself. So, if the camshaft sensor or the camshaft itself are replaced – it is necessary to perform the engine re-adaptation, paying special attention to creating the camshaft sensor’s adaptations! Install only OEM camshaft sensors! The quality of these sensors is the main key to the even performance of the engine!