In this entry, I will tell you a bit more about control of the exhaust gases for these complicated engines – what nuances have to be taken in the account to pass the Technical Inspection and exhaust gas test successfully.
In the TI, for petrol engines the amount of CO and HC in the exhaust is checked – these chemical compounds are harmful to the environment.
I will try to be consecutive, and at the end of the entry will add a list of related articles, where you will find more detailed information.
To control the proportion of the fuel, MSD80 uses 3 or 4 Lambda probes (two wide-band and one or two – narrow-band probes) – in this, there is no significant difference from “regular” engines.
These probes are placed in the exhaust system – before and after CO catalytic converters. Also there – nothing unusual.
As we know, N43/N53 series engines can perform in 3 different modes:
a) Homogeneous (or “usual” engine) mode;
b) Homogenoeus lean mode (unique for N43/N53);
c) Stratified charge mode (unique for N43/N53).
When the engine runs in Homogeneous mode, its performance doesn’t differ from the performance of “regular” engine:
a) MSD80 maintains correct fuel mixture, using wide-band Lambda probes;
b) CO catalytic converters are reducing the content of CO/HC in the exhaust;
c) control probes are controlling the performance of the CO catalytic converters (and are calibrating wide-band probes).
NOx system is not in use – it’s no need for it because in case of the Homogeneous mixture the content of NOx in the exhaust after CO catalytic converters is low (NOx is burned to N and O2 using CO converters; as we know, “regular” engines don’t have the NOx system at all).
Exactly in this (Homogenous) performance mode, the engine produces a large amount of HC and CO in the exhaust, so we will look at this mode more specifically. If the engine works in Homogenous lean and Stratified charge modes, the amount of CO and HC in the exhaust is tiny, exhaust test in the TI will not give any trouble.
Note: in the Stratified charge mode, the engine produces larger amount of NOx gases (NOx system is used to reduce these gases because of low efficiency of CO converters at these conditions), but the amount of NOx is not controlled during Technical Inspection. Also, when the vehicle is not driving (standing idle or with increased RPM), the amount of NOx is relatively small – it (amount of NOx) rises under load conditions. But no TI provides using of the dynamometric stand (even if some day TI will decide to control NOx amount), which means – if the engine on the moment, when the exhaust gas test is performed, works in Stratified charge, there will be no problems passing the test!
Due to the specific of N43/N53 series engines algorithm, the Stratified charge is not guaranteed even in circumstances, when all systems of the engine are in perfect order. There are several reasons, why N43/N53 can switch to Homogeneous mode:
a) decreased temperature of the engine or exhaust;
b) performance of specific service procedures (calibration of wide-band probes, the performance of tests of cylinder mechanical efficiency for Homogeneous mode and similar);
c) work mode – increased load (generator – the battery is getting charged, several consumers are turned on, air condition is working);
d) saturated NOx catalytic converter: relatively long (more than 2 .. 3 minutes) performance in Stratified charge at idle etc.
The main conclusion from all described before – we can not rely on a Stratified charge when performing the test of exhaust gases, and the vehicles have to be able to perform this test also running in Homogeneous mode. Therefore in the sequel – about some nuances exactly for the Homogeneous mode.
The Homogeneous mode has several specific nuances, which are typical for direct injection (to which belongs N43/N53) engines.
First nuance: rail pressure of direct injection is 30 .. 70 times higher than for “regular” engines (150 .. 200 bar opposed to 3 .. 5 bar), opening times of injectors: much shorter than for “regular” engines. These short opening times of the injectors (which ensure multipoint injection, and also the possibility to inject the fuel at the moment before ignition – in the compression cycle) are possible, thanks to piezo injectors – they have very short reaction time.
In the same time, these injectors have their weak spot – they have a (relatively) wider scattering of the reaction time than for “old type” injectors. This problem is partly solved by coding – each injector is measured by the producer, its data – coded in DME. But the situation is even worse – this reaction time significantly changes depending on temperature; voltage, supplied to the injector; usage of the injector etc.
If, for example, average fuel amount, intended for injection, in idle is 6 mg/stk (opening time: 0.2 ms), MSD allows 3 .. 9 mg/stk (0.1 .. 0.3 ms) correction of real flow-rate! It means a triple scattering of real flow-rate for short opening times is allowed!
What consequences have this scattering of the parameters? In idle and in small/average load the engine (if only appropriate measures are not taken – information will follow) runs unevenly – with permanent vibration, because the fuel amount, injected in each cylinder, is different.
But there is a much more important problem than vibration – it’s increased CO/HC in the exhaust. Why it’s happening?
Even if the Lambda probe allows to reach ideal proportion of the fuel mixture in the exhaust, it can not change, in any way, the fulfillment of the cylinder, it means: if the injector of one cylinder injects less amount of fuel, but the injector of next cylinder – increased amount of fuel, the fuel mixture of these cylinders will not be optimal, even if the average fuel mixture of current bank (both cylinders) will be perfect. In this example, we will assume, that Lambda of the first cylinder is 1,2; Lambda of the second cylinder: 0,8; average Lambda is perfect: 1,0. Anyway, you can change the average Lambda, there is no way to reach accurate fuel mixture in each of cylinders.
In the image: the content of the exhaust gases of petrol internal combustion engine (before CO catalytic converters).
In the existing sample – the fuel mixture in first cylinder will be lean, after then the air leftovers will get in the exhaust and increased content of HC (also increased CO content, because of the lean mixture, the misfires will start); in the second cylinder the fuel mixture will be rich, after that the unburned and partly burned fuel will become in the exhaust: increased CO and HC amount.
Of course, not just like that the CO catalytic converters are installed – the task of these catalytic converters is to reduce the content of CO and HC. But also the performance of the catalytic converters has its limitations – if the content of CO and HC is excessive, also after these catalytic converters the amount of CO and HC will be increased.
In such situations, the CO catalytic converters have several problems:
a) increased load of CO catalytic converters decreases its life expectancy and efficiency;
b) MSD80 records error messages regarding the insufficient performance of CO catalytic converters, starts to heat them up reinforced, even more decreasing the life expectancy, decreases max torque of the engine; KOMBI will light up EML signal lamp;
c) increased content of CO and HC after catalytic converter will not allow passing the exhaust gas test in Technical Inspection.
How the manufacturer solves the problem with a different reaction time of the injectors? With individual adaptations of the cylinders, already mentioned in many entries!
How is it done?
MSD80 measures the mechanical efficiency of each cylinder (tests of mechanical efficiency) or proportion of fuel mixture (chemical tests) and corrects opening time of the injectors in such way, that the perfect fuel mixture is reached in all cylinders in all possible circumstances. In reality, it means, that several tenths of different multidimensional adaptation maps are created, after a certain time the chemical efficiency tests are performed, while driving; in idle – continuous tests of mechanical efficiency are performed.
These tests of cylinder efficiency are possible (with reaching the desired result) only then if ALL systems of the engine are performing perfectly. As soon as MSD80 self-diagnostic system detects any smaller issue – for example, problems with regulation of temperature (thermostat, water pump), oil pressure, not even talking about fuel pressure – these tests of cylinder performance will be stopped and the engine will continue to run with simplified algorithms.
What are the consequences of such performance mode?
a) idle – permanent vibration is observed;
b) in small/average load and high load with low RPM – vibration, decreased torque;
c) error messages regarding CO catalytic converters, fuel trim are possible;
d) increased amount of misfires in several cylinders;
and also all problems with the increased content of CO/HC in exhaust and problems with passing the exhaust gases test in the Technical Inspection, mentioned before.
First substantial conclusion – as even if not unrelated problems: error messages regarding water-pump, defects of the thermostat, error messages regarding oil pressure etc., can be a cause, why there are several as if not imminent problems with fuel mixture and exhaust gases!
But because of the problem, described before, very often the injectors, CO catalytic converters HPFP and other components are replaced unjustifiedly.
Why sometimes these repairs as if helps?
a) when performing such expensive repairs, usually also defects, identified by MSD80 self-diagnostics are solved;
b) re-adaptation of the engine is performed (it’s required by ISTA D repair plan after replacing injectors and other significant repairs), which, at least for some short time (if all problems are no solved), restores the creation of cylinder-individual adaptations and normalizes the performance of the engine.
Defects of which systems are the reason to stop cylinder efficiency tests?
As already mentioned before – as if not connected and as if minor defects. In turn, for example, the error messages regarding fuel pressure, VADOS, DISA, NOx system, will cause even more recognizable problems.
Depending on many circumstances (number of defects, circumstances of its registration etc.), MSD80 is able to modify following functionality (which is linked to optimization of fuel mixture):
This list is arranged in sequence “from smaller to larger damage”. Balancing of the cylinder performance in idle is turned off as the first solution in case of damage of any system; if the damage is more serious – the balancing of the cylinder performance while driving is also turned off etc.
problems with water pump will cause (a) and (b); problems with oil pressure – (a), (b), (c), possible – also (d).
Problems with NOx system are causing: (a), (b), (e), (f) and after certain time also (g) and (h).
One more important nuance (mentioned for several times in other entries) – if the engine has limited its functionality for some reason (error messages regarding some defect are recorded), full functionality usually (there are very few exceptions) is NOT RESTORED automatically!
To restore full functionality:
a) solve all problems;
b) delete the error messages;
c) delete old adaptations and re-adapt the engine.
In simple words – perform certain service operations, using ISTA D or INPA, and ONLY THEN the desired effect will be reached.
The effect will not be reached, only replacing the damaged spare part and deleting error messages regarding it!
Returning to the topic of the exhaust gases – all mentioned before regarding solving problems of all systems, deleting adaptations, re-adaptation of the engine is CRITICALLY important! If the engine has (as not even related to fuel regulation) at least one damage of the system, with very high possibility – the content of CO/HC was increased. If, performing the repair, even one of the required service procedures will be missed – no positive result (even performance of the engine and CO/HC content, corresponding to norms) will NOT be achieved even in a situation when all engine components are in perfect order!
Not following the correct order of service procedures, you will replace (unjustified) the injectors, CO catalytic converters, Lambda probes – you will spend several thousand EUR for no reason.