Idle. Stratified charge. Part 3

As already mentioned here, in idle (also if the Stratified charge is used), injection is done with two portion method.

Here you can find information about correction, applied to the injectors in idle, and also live data. So far everything seems clear.


First 3 rows in the picture – opening times of injectors.


Corrections of injectors (idle, Stratified charge). First 3 lines – reference values, next three lines – live data.


But – everything is not so simple.

MSD80 knows how to measure leaking of injectors and how to identify in idle: how large part of correction (when the evenest performance mode in idle is reached) is due to changes in reaction time of injector (differences from one, defined by manufacturer/encoded on its body) and how large part of correction is due to incorrect/poor injection of fuel (the fuel has poor atomization – if burns worse, and due to this reason, the cylinder has decreased mechanical efficiency).


How MSD80 does that?

In idle, when Stratified charge is used, MSD provides the test – changes the proportion of both following injection portions. Once in two-three seconds, the proportion of these impulses is changed to 1:2 or 2:1 and back, keeping the amount of injected fuel unchanged.

The first portion of injected fuel (and also fuel, which has gotten in the cylinder due to, possibly, leaking injector) mixes with air very well – it’s enough time for it. Instead, the last injected portion is burned as it gets in combustion chamber. So, if the injector (due to some defect) don’t inject the fuel as a tiny mist, problems are guaranteed – this second portion of fuel will burn badly, the mechanical efficiency of cylinder will be reduced, half-burned fuel will get in the exhaust.


So – MSD changes proportion of both injected fuel portions and observes mechanical efficiency of cylinder. In the case of correctly performing injector, mechanical efficiency won’t change during tests, but, if the fuel atomization is poor, the efficiency of cylinder will change during test (will improve, when more fuel will be injected in the first portion).


Make attention to the opening time of cylinder 4.


When MSD does that?

With high priority – after deleting adaptations (during the creation of new adaptations) and, if increased unevenness in idle is detected. In other cases – after a certain count of motor hours, with lower priority.


Why MSD does that?

Of course, MSD cannot eliminate problems of injectors – if some injector injects fuel not in an ideal way, the situation can be changed, only replacing or cleaning it. But, MSD have to know, how to react, if the mechanical energy of cylinder has to be changed (for example, if a load of engine changes – when AC is turned on; the load of the alternator has increased, etc.), changing RPM (in range of small RPMs), or correcting unevenness of the idle. Knowing exactly, how large part of corrections refers to the reaction of injectors (offset type correction), and how large part – to the quality of atomization (multiplicative type correction), MSD can predict the behavior of the injectors very precisely.


Interesting nuances

Of course, there is no exact information from the manufacturer, so I can only make observations. Correction, which refers to the leaking of injector and atomization, MSD will apply to the first impulse of injection, for the other impulse the only correction of retention time (encoded on the injector + measured) is added. Diving the components of this correction, also the math of injectors management gets easier. Accordingly: ../F5/Shift+F6/F1 opening times in idle shows the length of the second impulse and ../F5/Shift+F6/F5 part of applied correction, which refers to the correction of retention of the injector.

Instead, ../F5/Shift+F6/F5 correction part, which refers to atomization and leaking, is applied to the first impulse of injection and in ../F5/Shift+F6/F1 cannot be seen (is not included).

If required correction is beyond value when the length of the one impulse drops to 100 us, also the another impulse is shortened. This method (of strong correction) is used if necessary correction is higher than around -1.5 mg/stk.

By -3.0 mg/stk, length of both injection impulses drops to the minimum allowed: 100 us. If with such (around -50 %) correction is not enough to even the mechanical efficiency of the cylinder, MSD records the error message regarding overrun of the correction value of the injector.


At the end

I remember the times when my car has problems with NOx system (error message 30E9). Then, the turning on of the AC happened with a “hit”. In the same time – when the NOx system was restored, this defect also disappeared. The AC turned on very smoothly. For a long time, I was thinking – a software bug. But now it’s clear – AC didn’t turn on as supposed, because MSD had no options (Stratified charge was not working) to measure the quality of atomization and response time parameters of injectors and accordingly – correctly manage the injectors in idle at rapidly changing conditions.


I have to admit – I’m truly impressed with work, done by Siemens (and BMW as an author of a technical assignment)! And how many still undiscovered features…