N20. Injectors fail

This situation happened to my “office brother”. If I haven’t seen the current problem by myself, I would be very skeptical. Right, for this reason, I wrote this entry.

Customer: F10, N20 engine. Manufacturing year of the car: 2013. It means MEVD 17.2.9 (upgraded software) with the electrical wastegate.

Current situation: the owner of the vehicle has performed the repair by himself. A while ago, a strong vibration of the engine was observed; diagnostics (more precisely – reading of the error messages) have indicated the HPFP problem (actually – error relating to drop of the Rail pressure was stored). The pump was replaced with a new one. The problem hasn’t disappeared. Then the owner of the vehicle replaced all injectors. To new ones. The problem still persisted.

At this moment, I was asked to “just take a look” in this case.

There won’t be many images in this entry – I will try to keep it compact.

The re-adaptation was performed to the engine, with no error messages in the DME error message memory.

Cold start. The engine starts normally. As soon the wideband probe (DME switches to closed-loop mode) starts to work:

  • idle RPM starts to fluctuate strongly;
  • sometimes the engine even shuts down;
  • mechanical efficiency of cylinders indicates fluctuating efficiency of each cylinder, but all cylinders are performing likewise (the average mechanical efficiency is close to 0: leveled), misfires are not observed.

The values of all essential parameters (air mass, RPM, even Lambda) are fluctuating so strongly, that it is practically impossible to understand, where is the cause of the problem.

When the engine is warmed up, it works more or less acceptable, but when it is cold, it performs very incorrectly. Even a cheap car is not supposed to act in such a manner! Not even talking about BMW – with new HPFP and new injectors installed!

It is clear that one of the two basic parameters:

  • the amount of air;
  • the amount of fuel;

is completely inadequate.

My recommendations were:

  • measure the true Rail pressure, its compliance with the data of the sensor (and the stability of the fuel pressure should be evaluated);
  • check the air-tightness of the CCV and inlet manifold.

Some reliable basic parameters, on which can rely, should be acquired!

For these engines, BWM AG “made it easier” for diagnostics specialist to work with them:

  • no Offset type LTFT data are available;
  • no Integrator data are available;
  • no Lambda values are available (only Voltage is displayed);
  • no LPFP pressure data (there is no sensor, who would measure the pressure);
  • no data regarding corrections/adaptations of the injectors are available.

In this exact case: it is not even clear – is the initial fuel mixture too rich or too lean (DME managed to “reach” correct fuel mixture, but the amount and ”polarity” of corrections was not clear).

After a day, my colleague calls me and tells that the blocking of the CCV inlet has not given the expected result. But there is other news – it turns out that the owner of the car installed the injectors, intended for EU5 (not compliance with this/upgraded engine), not EU6 (required). It is possible that he managed to “save” some money.

A colleague expressed the opinion that the injectors could be the culprit. I was very skeptical. The basic parameters (for example: flowrate) of both types of injectors (EU5 and EU6) are identical! And… I was wrong!

The confirmation that exactly the injectors were the cause of the problems during a cold start:

  • installing new EU6 injectors, after re-adapting the engine, it works perfectly;
  • installing two old (the injectors without defects were identified; one strongly leaking and one dripping were recognized as damaged) EU6 injectors + two new EU6 injectors – the engine works perfectly;
  • installing two old EU6 injectors and two EU5 injectors – the engine has all typical symptoms;
  • installing two old EU6 injectors and two new EU6 injectors and also the old HPFP – the engine works perfectly!

It is clear that the owner of the vehicle has replaced HPFP and two injectors without justification. Even more – wasted money by purchasing four inappropriate injectors!

There was no doubt also for me – the cause of the fluctuation in idle during the cold start: injectors.

But – where is the cause of the problem?

At that moment, I remembered the BMW AG materials regarding beam features of the new EU6 injectors. The nozzle has 6 beams, but their flowrate is different:

  • two beams, which are directed to the exhaust, are with reduced flowrate;
  • four other beams are with increased flowrate. The difference between their flowrate is 30%.

During the warming of the engine, DME of N20 creates two injection impulses. The second impulse is performed very lately, with a thought – so the part of the fuel gets in the CO catalytic converter and warms it up more quickly.

Obviously, the changed geometry of the fuel injection gives such a big impact in these conditions and (comparing with the injectors with symmetrical flowrate) so different mechanical efficiency/fuel mixture of the cylinder is created, that DME is not able to correct it!

Yes, it is possible that in “old” N20, the newer EU6 injectors can be used, but it is clear that for “new” N20/B48/B58, the EU5 injectors can NOT be used!

One more exciting nuance: manufacturing year of these EU5 injectors – 2019. So – these “old” injectors are still in manufacture!

There are many unanswered questions, for example:

  • are these EU5 injectors some rejected (not trimmed) EU6 injectors?
  • are the EU6 injectors of the “middle generation” with asymmetrical beam flowrate?