The lifespan of the CO converter

Quite often can hear – 20 years ago everything was better! BMW served forever; it wasn’t possible to damage the CO catalytic converters of the petrol engines! In contrast, for nowadays BMW, the error messages regarding the CO catalytic converters can be seen even for cars with mileage of 70’000 .. 100’000 .. 120.000km. The CO catalytic converters have become fragile? Does BMW manufacture low-quality CO catalytic converters? Are the users of the car to blame? Where the problem hides?

First significant nuance: starting with an N series, BMW introduced a completely different method of measuring the CO catalytic converters. If for M series engines, the performance of the CO catalytic converters was checked, using pulsations of the control probes voltage, then for N series, the performance of the CO catalytic converter is measured in a much more advanced way. In addition to the already known method (in case of N series, it indicates, do the CO catalytic converters have kept the minimum of the efficiency), an additional method is introduced. For N series, on the go (in different driving conditions), DME for a moment introduces air in the exhaust, after a short moment – an additional amount of fuel. At the next step DME measures the time in which the fuel, introduced in the exhaust, is (or is not) burned.
So – in the case of the M series engine, the ability of DME to measure the performance of the CO catalytic converter was very limited. Accordingly – it is possible that also the “old” CO catalytic converters lost their efficiency as fast as the “new” catalytic converters, only – the user of the car was not informed about it!
Still to be considered – when performing TI, the engine of the car runs without load; accordingly – also the load on the CO catalytic converters is low. Emissions will fit into the norms, even if the performance of the CO catalytic converters will be only 5 .. 10% of new catalytic converters. In contrast, the advanced control system of the performance of the CO catalytic converter will light on the EML already by much higher thresholds.
For example, for my everyday car, when the mileage of 430’000 km was reached, the error messages regarding CO catalytic converters were recorded regularly, for several times also EML was lighted up. At the same time, the content of CO/HC in the measurements of TI was low. CO around 0.015%; HC around 30 ppm (allowed: CO – 0.2%; HC – 100 pp).

Returning to the problem – shortened lifespan of the CO catalytic converters.
It is clear that the car is designed for a lifetime of at least 200’000 km; accordingly – also the CO catalytic converters should last at least for so long. Why sometimes do they not serve even half of this resource?

N42/N46/N52/N62, etc. with Valvetronic
Problems of these engines start due to long intervals (which usually are defined for 30’000km) between oil changes. So rare oil changes create problems for HVA (they are clogged). As a result, by low loads and in idle Valvetronic works incorrectly – the valve openings in different cylinders differ. Accordingly – the fuel mixture in cylinders is different. In some cylinders, the fuel mixture is rich, in some cylinders – lean. The leftover of fuel and air is burned in the exhaust – in CO catalytic converters. Accordingly – the CO catalytic converters are overloaded and worn out quickly. After mileage of 150.000 .. 200.000km, a typical engine with Valvetronic (if the oil changes are performed after 25.000 .. 30.000km) cylinder’s efficiency disbalance reach 30 .. 50%. Accordingly – almost half of fuel in idle and low load driving conditions are burned in CO catalytic converters!

These engines do not have Valvetronic. However, they have piezo injectors, which parameters can differ for even 3 .. 4 times (in a range of idle and low loads)! So – the same problems with an incorrect fuel mixture are guaranteed. But this time, instead of problems with HVA – problems with the NOx system. If this system is damaged, DME turns off the Stratified charge, does not performs a range of complicated measurements of the injectors. If the injectors are not measured, the compensation of the differences of their parameters is not possible. And – already familiar (previously mentioned) scenario damages the CO catalytic converters much faster than intended by the manufacturer.

This engine has both – piezo injectors & Valvetronic. Yes, this engine is very demanding regarding timely oil changes and also the quality of the fuel.

Common for all these engines – piezo injectors, which tend to leak during the cold start, tend to be stuck in an open position. If these problems are not solved immediately – problems with CO catalytic converters won’t make you wait long.

N54/N55/N63 and similar, with turbochargers
For these engines, in addition, the “upgrades”, made by chip tuners to increase the power should be mentioned. I have ever seen a correct result. In all cases, which I have seen till now, DME continued to work in limp mode: did not measure the injectors; the fuel mixture in cylinders was incorrect. As a result: the CO catalytic converters are overloaded, their lifespan – significantly shortened.

Problems, common to all engines
Here I have to mention the non-compliance with service procedures. If, after the repair, a correct re-adaptation of the engine is not performed, DME does not restore full functionality, even if all problems are solved. Without a correct re-adaptation – all repair job is useless!
A second significant nuance – a very limited circle of repair specialists are able to correctly identify problems of the injectors. The necessity of the NOx system usually is not evaluated at all. Additionally, in ISTA, the data of the injectors are not available. Accordingly, the specialists of the dealer centers are not able to evaluate the performance of the injectors at all (it is not allowed to use INPA in the dealer centers).
My experience says: if the N series engine is kept in technical order, its CO catalytic converters will serve 300.00 .. 400.000km without any problems!

An example with my everyday car
According to the AIR data:
a. the NOx sensor was replaced around mileage of 20.000km;
b. the same procedure was performed around a mileage of 40.000km again.
After the 2-nd replacement, the dealer obviously got fed up with neverending problems with the NOx system.
When I purchased this car (with mileage slightly above 100.000km):
a. the error message 30E9 regarding the insufficient performance of the NOx catalytic converter was active;
b. the error messages regarding the CO catalytic converter of the 2-nd bank were recorded on a regular basis (starting already with a mileage of 90’000km);
c. all possible error messages regarding the NOx sensor were recorded (starting already with a mileage of 60.000km).
So – as if already serious problems with the CO catalytic converter of the 2-nd bank?
The problem was with the fuel mixture in cylinders. The fuel mixture in cylinder No.5 was lean, in cylinders No.4 and No.6: rich. As a result: regular misfires in cylinder No.5, which did not disappear even after replacing the ignition coil, spark plug, and injector. The CO catalytic converter of the 2-nd bank was overloaded, and due to this, its efficiency was reduced. After the repair of the NOx system, DME remeasured the injectors and evened the fuel mixture in cylinders No.4, No.5, and No.6. The error messages regarding the CO catalytic converter of the 2-nd bank were gone and appeared only after a mileage of 400.000km!

The second example
The owner of the E90, N43 series engine, approached me. Classical problems with the NOx system, nothing special. This time I will mention the temperature of the exhaust system:
a. before repair – idle, Homogeneous mode: around 350 oC;
b. after the repair – identical conditions: 160 .. 170oC.
A huge difference! There is no slightest doubt – before repair, a huge amount of fuel was burned in CO catalytic converters! Of course, the CO catalytic converters are not able to endure such a huge load for a long time.