CO catalytic converters are an expensive spare part, so the question “do they really need to be replaced”, is very significant. Significant enough, to dedicate more time to explore and evaluate the performance of the catalytic converters.
The situation is aggravated by the circumstance, that the information from the manufacturer is 0, pass/fail tests, reported via OBD 9 mode (more info here) are without additional information.
My observations suggest, that MSD80 (I assume, that also MSV70/80; MSD87/85 and other newer DME) act in a similar way:
a) measures the performance of the CO catalytic converters (with an interval: around 100km by Vavg = 50km/h) in the exact driving (load to the catalytic converters) conditions; if the pass % of the last X (around 15 .. 20) tests is below the allowed threshold (around: 40%), the appropriate error message regarding reduced performance is recorded, the “reduced” status of the catalytic converter is set as “active”;
b) if the reduced status of the CO catalytic converters performance is set as active, the load to the CO catalytic converter is reduced (to reduce the emissions of CO/HC): the enriched mixture (with Lambda below 1.00) in kick-down mode is limited to the engine, “softer” curves of the exhaust VANOS are used, max torque is limited, the reaction of the engine is slowed down (to make sure with help of Lambda probes that Lambda corresponds exactly to 1.00, not as in the mode of full power – it would work according to the adaptation maps). The engine becomes “clumsy”, it looses some power;
c) deleting of the error messages does not change the status of the CO catalytic converters – it is changed (restored as “normal” ) only when the performance tests of the CO catalytic converters confirm, that the performance of the CO catalytic converters is restored. Deleting of the error messages only givers a certain “handicap” with a purpose – if before the deleting the CO catalytic converter was replaced with a new one, no fake error messages will be recorded (due to one/two unsuccessful tests directly after replacement of CO catalytic converters);
d) if DME has confirmed the reduced performance of the CO catalytic converters, during following tests (tests of a reduced load of CO catalytic converters) the amount of fuel left-over, which has to be burned by the CO catalytic converters, is also reduced (to make sure, that also during the tests the emissions of the CO/HC would not be catastrophically excessive) and accordingly in set 2 .. 3 times lower threshold for the necessary performance of the CO catalytic converters for tests to me acknowledged as performed successfully;
e) if during the time of the next tests (in a situation when the reduced performance of the CO catalytic converter is detected) the catalytic converter successfully passes the exact % (increased against the “normal” status) of all tests (with reduced requirements to its performance), the performance status of the CO catalytic converter is restored to “normal”, requirements are increased to the initial ones. The status of the error message is changed to the “not active”, the engine regains full torque and “sharpness”;
f) DME continues to test the catalytic converters by the “full program”. If the tests of full performance fail again, the performance status is repeatedly switched to the “reduced”, the error message status – changed to “active”, etc.;
g) even if the number of pass tests of reduced performance is not above the required threshold, EML symbol in the KOMBI is lighted up because it’s clear – if even in the mode of reduced power the engine is not able to burn the left-overs of the fuel and ensure the more or less acceptable level of CO/HC in the exhaust.
In such a way, the DME observes the ecological requirements and continues to control (and, if possible – restore the full power of the car) performance of the CO catalytic converters even in case of any problems in their performance are detected.
Note. The intervals and the “length” of the impact of the performance tests of the CO catalytic converters could be related to the following logic: one tank of low-quality fuel can not cause catastrophic consequences. In the existing situation, test data include the range of at least 2 full fuel tanks. Accordingly – if the owner of the car has filled one tank with a low-quality fuel (which can cause short-term reduction of the efficiency of the CO catalytic converters), the test results will get worse, but not so significantly for the EML symbol to be lighted up in KOMBI. In the case of good catalytic converters – even the error messages will not be recorded. At the same time – during several thousand km the performance of the CO catalytic converters will be more exact – that is fast enough.
The main problem – counters, reported via OBD mode 9, are common for both (normal and reduced performance) modes. For N43/N53 engines – common also for Homogenous and Stratified charge modes (although the error messages regarding the performance of the CO catalytic converters of both modes are separated). If there is no exact information, what was the status of the catalytic converters (was the error messages with status “active” recorded), the pass/fail number alone don’t give correct information.
For example, a pass coefficient of 60% in “reduced” mode will be the quite worse result as a 50% pass coefficient in “normal” mode. And, as mentioned in the first part of the blog – exactly the results of the last several tens of tests should be inspected, not the average indication since the “born” of the car.
Even more – it is possible, that DME uses not a fixed “reduced” coefficient, but variable, depending on the driving conditions. It makes the evaluation of this pass indications even harder. Also “pass/fail”, most probably, is not a fixed value, but the parameter of the performance of the catalytic converters (a number). Unfortunately, the exact math is known only to the developers of the software. We can only try to evaluate the test results by the available information.
How to act to evaluate the performance of the catalytic converters?
One of the techniques:
a) re-adapt the engine;
b) evaluate the results of the first 10 .. 20 pass/fail tests directly after the re-adaptation of the engine.
If the engine has no fundamental problems with creating the adaptations of the fuel mixture, during several first motor hours correct fuel (basic) adaptations are created, and the evaluation of the CO catalytic converters can be started.
It goes without saying – if the error messages regarding CO catalytic converters are recorded during the first tenths of km – the situation looks sad.
If the error messages regarding CO catalytic converters are not recorded during the first 10 .. 15 .. 20 tests – it is only logical to assume, that the performance of the CO catalytic converters (al least for now) is set as “normal”.
From my experience, I conclude, that the approximate threshold pf pass/fail coefficient is around 40%. If the pass of the CO catalytic converter is below it, it can expect the error messages regarding CO catalytic converters and “reduced” status with decreased requirements to the performance.
A second technique:
record (count) pass test events, at the same time marking the status of the error message regarding CO catalytic converters. This method requires regular (after each 50 .. 100km) inspection of the pass/fail list during a longer period (1000+ km). In this case the pass coefficient in “normal” mode and “reduced” mode. In the first case, the critical threshold is around 40%; in “reduced” mode – at least 70 .. 80%.
Yes, both methods are time-consuming, but the price of the CO catalytic converters – high (even more than EUR 1500 .. 2000). It is up to each one to evaluate, how much time/energy is worth to invest.
Unfortunately, there is no information, in what modes which test (catalytic converters, the temperature of the engine, load, RPM, etc.) of the catalytic converters is performed. These data would allow a better understanding of the bad results of the tests that are not caused by a very incorrect driving profile (for example, regular driving with a very low load). There is also no information if the fail list includes also tests, which have failed due to other reasons (for example, a swift change of driving conditions).
In the end: observation says, that DME performs the tests of CO catalytic converters also if it has not reached full functionality mode (all its systems work correctly and it has finished all critical adaptations). In this case, the tests of the CO catalytic converters are not considered reliable – no consequences (switching of the modes of the CO catalytic converters, recording of the error messages regarding their performance) are assumed. Accordingly – bad news regarding the poor performance of CO catalytic converters expect the owner fo the car after repairing all other systems of the car.