The user of the N53B30U0 engine (325i) from Milan, sunny Italy, got in touch with me. He approached me as a well-known chip tuning skeptic to prove that not everything is so wrong. His car just had undergone an impressive and expensive rebuild, which has an excellent result. Even more – everything is perfect!

Derogation: N53B30U0 engine (installed on 325i and 525i) provides a torque of 270Nm, limited by the software, in a wide range (from around from 1500 RPM till 5000 RPM) and power of about 220 hp. After a slight rebuild (inlet manifold with 2 DISA valves and changes in the DME software), the engine “turns” into the most powerful O0 modification (as installed on 330i and 530i), and the torque in a broader range increases to 320 Nm, and power – to 272 hp (200 kW).

But, not in this case. Owner of this car choose another way. Here is the exhaust system used in this exact project:

The exhaust really looks like a quality build. Unfortunately, such exhaust means no more place for CO catalytic converters. CO catalytic converters are moved to the location of the NOx catalytic converters, and OEM CO catalytic converters are replaced by alternative solutions.
The car’s owner informed me that everything was perfect with the exhaust gases. ”The car corresponds to the EU4 normative because it has passed the emission tests”. But here are some notes. First – the fuel used was not E92 ..98. Second – during the TI, the emissions are tested without load to the engine (on idle/increased RPMs). To successfully pass the TI is enough, even with several % of the initial (manufacturers/OEM) performance of the CO catalytic converter! Accordingly, there is no “drop” of correspondence to EU4!

And here is the report of the dyno stand (tuning company):

Has the rebuild given a result? Undoubtedly! I have to admit – this is the first time in my experience with these engines that I can say – yes, it can be clearly seen that the throttle is completely open; yes, in kick-down mode, a full-throttle is “squeezed” out!

But let’s see these graphics more closely.
Stock solution (rebuild U0 version to O0) guarantees 320 Nm, using E92 fuel. With E98 .. 100-grade fuel and air filter of increased flow, the measurements in a wide range typically indicates at least 330 Nm torque. Power – around 285 hp. This graphic shows a torque of 340 Nm in a narrow range of RPM. Such gain (against the stock O0) corresponds to about 3% and is comparable to the error of the dyno stand (even if the stand is calibrated and in perfect technical order; in the opposite case – the error is much higher). Instead, range of 1500 .. 4000 RPM, the torque is much lower after rebuild than for the stock O0 engine.
My verdict is quite harsh – in a wide RPM range, the result lags behind the stock O0; in a range of 5000 .. 7000 RPM, it practically corresponds with O0 (measured in identical conditions, including fuel).

I expressed my doubts regarding the ability of DME to work correctly without CO catalytic converters (in their intended places) and in Stratified charge. My suspicions were confirmed by the owner of the vehicle when after several days. He informed me that in the DME error message memory following error messages had appeared:
a: trim of the wideband probe(s);
b. signal plausibility of the control probe(s);
c. performance of the CO catalytic converters in Homogeneous mode (due to defects of the NOx system, Stratified charge is not used).

First bad news – if/when DME identifies the reduced performance of CO catalytic converters, the engine’s max torque is limited (reduced). So – from the excellent torque we have… Zero.
Second bad news – for these engines, it is impossible to correctly switch off the control probes or install some kind of emulators for them. Control probes are used to trim the wideband probes; if they are switched off – the average fuel mixture will be wildly incorrect. Reason – untrimmed wideband probes are “lying” to DME.
Third lousy news – if the injectors are not measured (and they are not measured, if the engine does not use Stratified charge, in this case – additional problems with the probes, which completely paralyze any fuel adaptations), the individual fuel mixture of cylinders will be even less correct than the average (of the bank) fuel mixture!
The flowrate scattering of these piezo engines (new! injectors) in conditions of long openings is at least +/-5 .. 10%, which means: if the differences of the injectors are not compensated, in one cylinder, the fuel mixture can be with 5 .. 10% fuel leftover (rich), in another – with 5 .. 10% air leftover (lean). Yes, a lean fuel mixture will cause detonation, and it will not take long until the engine is damaged.
Fourth lousy news – such incorrect fuel mixture of cylinders overload and damages the CO catalytic converters very fast. This problem is indirectly identified by the error messages regarding probes and (already recorded) error messages for new catalytic converters regarding performance loss.

Are there any reasonable solutions?
By idea – we could try to “move” the control probes after new CO catalytic converters (maybe we would manage to avoid the error messages regarding the plausibility of the probes). Unfortunately, the experience of others indicates that for these engines (due to specific injection modes), only OEM CO catalytic converters can be used. The NOx system and Stratified charge should be restored. The inlet manifold of the O0 version should be installed. The Power class parameter should be modified from 00H to 02H. Respectively, this current rebuild has created only problems and losses without any gain over the O0 version.

Unfortunately, after receiving my verdict, the owner of the vehicle was noticeably sad because the budget of the project (not small) was spent, but the perspectives – were very sad.
Remember – in the BMW factory, no idiots are working!