A customer of the service of an acquaintance experienced a problem – cylinder No.5 was stubbornly refusing to work.

I performed the diagnostics. The initial situation was the following:

  • records regarding turning off cylinder No.5 due to misfires;
  • during the cold start, increased mechanical efficiency of cylinder No.5 observed;
  • my diagnosis –  some injector of the 2-nd bank (more precisely – of cylinder No.5 due to increased mechanical efficiency) is leaking. The Integrator is -30%, and even with such correction Lambda is 0.80 .. 0.85 (what is important – does not reach 1.00).

In idle, the engine was vibrating, cylinder No.5 was turned off regularly. In this case, also the adaptations could not be blamed because the NOXEM was installed in the car, and the vehicle was readapted.

In my opinion, the symptoms are unequivocal – accordingly (with an increased mechanical efficiency), the injector is leaking. The defect is typical, nothing special.


But the mechanic of the service had an idea – may be the cause of the problem is a mechanical defect? Maybe the injector is not the culprit? In this entry precisely about that – can the mechanical deficiency cause the issues with such symptoms.


Where could hide the cause of the problem? The service specialist considers – no air accesses the cylinder.

Possibly, the specialist has read my blog, the entries regarding Valvetronic and HVA problems – from this, the idea of no air access. I assume this theme can be topical also for other readers of the blog.

Let’s look at the possible cause of the problem a bit closer. I will start with the mechanical side of the problem because it is much closer to the non-specialist of the diagnostics (but persons, who are well qualified in the engine design) and also the specialist of this current service.

It is clear – for the fuel successfully be burned in cylinder, two components are required:

  • fuel itself;
  • the correct amount of the air.

If we assume that there are no problems with fuel supply and fuel amount, the air is left.

Too much air? Doesn’t sound plausible – all cylinders have the same inlet manifold, the depression (amount of sucked air) in it is defined by the throttle.

The version of the service specialist was: is was not enough air. Is it possible at all?

Unlike many other N series engines (for example, N46, N52, N55, N63, etc.), the N53 series engine is not equipped with Valvetronic. It means – in idle (in the problematic conditions), the valves (like in other conditions) are opened with a max stroke – around 10mm. The amount of the air in cylinders is defined by the depression in the inlet manifold, which, in turn, is determined by the throttle opening.


Most important questions: what happens if the opening (lift) of the inlet valves is not correct? What should be the minimal lift of the inlet valves for us to consider that the problem is not in the amount of air?

The valve opening of N52B30 (the engine with identical volume with similar inlet valves) in idle (in full-functionality mode, when Valvetronic works) is around 0.3mm. Also, additional depression is also in the inlet manifold (it is defined by the throttle).

So, an opening of 0.3mm is enough to suck in the amount of air necessary for the correct fuel mixture. If we increase the opening of the valves (accordingly – opening cross-section) for 10 times – to 3.0mm, definitely  – in an idle valve lift is more than enough for the impact of valve would not be dominating. So, with a guarantee – if the valve opening is 3mm, the depression in the inlet manifold will be decisive in creating the fuel mixture. Here is the answer – it is entirely enough with a 3mm opening for the engine to run correctly in idle! And, let’s take into account – such reduced opportunity should be for BOTH inlet valves!

So, for the cylinder to suffer from serious air supply problems, the opening of both inlet valves should be reduced from 10mm to significantly below 3mm.

It is hard to imagine such a defect! Both valves do not open! In contrast, for other cylinders – everything is fine! No error messages regarding oil pressure! Live data of the oil pressure confirm correct pressure (I check it always).


But, let’s go deeper into the exploration.

Let’s assume that the valves have such a lowered opening. What can cause it?

Exclusively HVA. If the roller drag levers would be ultimately “drowned,” the valves would not open at all. But here – a sporadic defect, only – for a cold engine. Imagine the acoustic noise, if two HVAs would “give up” that the valves are practically not opening at all! I have never experienced anything like that!


Here, the blueprint of the parts of the N53 series engine inlet manifold. Pay attention to the support point of the roller drag lever (9)!

The lever (distance) to the valve stem is around 2 times shorter than the lever till HVA. This is done for the following purpose: reduce the impact of HVA on the “free movement” of the valve and reduce the pressure force on the HVA. According to the primary course of physics: to minimize the movement of the valve for 7mm – in the side of HVA the motion should be 2 times more massive, it means 14mm. 14(!)mm. How do you think – the situation that HVA can “give up” for at least 14mm is possible? It is not possible, even theoretically! Even if the moving part of the HVA will completely sink in the body, such free movement is not possible!


In my opinion – the problem mentioned by the service specialist is proved as impossible even theoretically.


But, we can see what other arguments also oppose this theory.

  • Lack of air means – part of the injected fuel has ejected in the exhaust unburned. If the cylinder has a lack of air, its mechanical efficiency in no way can be INCREASED! Its mechanical ability will be REDUCED!
  • Let’s assume that one of 3 cylinders of the bank really has a lack of air. In such a case, the average fuel mixture of the bank will be rich. Let’s assume that both inlet valves of the damaged cylinder do not open at all – scenario of the maximum defect. In such a case, DME (detecting rich fuel mixture) will reduce the amount of fuel injected in all cylinders proportionally. Reducing the amount of fuel for 33% (or 1/3) in each of the cylinders in the whole bank, the Stoichiometric fuel mixture will be reached. So, if the Integrator is -30%, Lambda should be around 0.97 (close to the 1.00 – Stoichiometric mixture). In such a situation in no way, there can be a fuel leftover of approximately 15 .. 20% or even more!

I believe the readers of the blog have no slightest doubt left that the lift problems of the inlet valves for these engines (N43/N53) CAN NOT be the cause of misfires and/or too rich fuel mixture in idle!