Idle. Measurements of mechanical efficiency

As already mentioned in other entries, modern engines are performing the measurements of mechanical efficiency in idle. Measurements are done, taking into account short-term speed changes of the flywheel. If the engine identifies efficiency, different from ideal cylinder efficiency, it changes the fuel supply in each cylinder to balance efficiency of cylinders and ensure smooth (as much as possible) idle.


N43/N53 have following performance modes in idle:

a) Homogeneous mixture with Lambda 1.00

b) Stratified charge with Lambda 2.00 .. 2.50


In each of this modes, MSD performs independent measurements of mechanical efficiency.


Adjustments, applied to Homogeneous mode (results of the last test), unfortunately, are not available.

Adjustments, applied to Stratified charge (results of the last test) are available here: ../F5/Shift + F6/F5

Bar of each injector marks corridor of admissible values – min/max value. Results of the test show corrections adjusted to reach even idle.

Results of “work” of both modes are seen here: ../F5/F7

Note: Rough run data are in firing order (1/5/3/6/2/4); increased efficiency: value below 0.


As already mentioned in previous entries, the normal performance of MSD in idle is characterized:

Rough run data on all cylinders are fluctuating around 0 value, it means, each bar has to change “polarity” from negative to positive, not less than once in 5 .. 10 seconds.


Following problem situations are possible:

a) Rough run bars are correct for some time, but periodically they fluctuate, the uneven running of the engine can be felt (shivering);

b) Rough run data are showing long-lasting unevenness (feels like a diesel engine), additional fluctuation also possible.


In the first situation – obviously, misfires are ones to blame. Accordingly – check misfire counters with EML327, as described here.

In the second situation – obviously, MSD works in emergency mode. Unfortunately quite often these situations have typical features:

a) no error messages recorded regarding this emergency mode (as consequences of the unbalanced fuel mixture, error messages regarding misfire can be recorded, but these are only consequences to functional impairments of MSD);

b) normal functionality is not restored, even if perfect components (injectors, coils, spark plugs) are installed and error messages are deleted.

Note: regular misfires of any cylinder can be the cause of long-term disbalance (MSD calculates the average efficiency of each cylinder, misfire cycles with 0 efficiencies are included in total calculation).


Reasons, why the equalization of cylinder efficiency in idle is disturbed:

a) incorrect coding of the injectors (input of data with incorrect control sum), description here;

b) correction, necessary for at least for one cylinder is out of min/max limits (absolute values of parameters – inadequate flow-rate of the injector during short openings);

c) equalization is disabled because of problems with other systems, for example: fuel pressure; oil pressure; water pump, VANOS, etc. More about this read here;

d) required correction for each cylinder significantly differs from previous situation. Detailed description here.


Regarding case a: as mentioned in other entries – check (re-enter) coding.

Case b is more complicated. Unfortunately:

a) Homogeneous mode – there are no indicators, which could point to this problem (no status bits, no appropriate error messages); as already mentioned before – no data of last corrections applied are available;

b) Stratified charge: as already mentioned before, data of last corrections are available here: ../F5/Shift + F6/F5


If any injector requires correction (to reach even idle), which exceeds allowed limits, MSD stops further equalization of idle.


Example: the correction necessary for the injector of cylinder No.6 exceeds permissible limits (the opening time of the injector is strongly decreased, but even with very shortened opening time the necessary mechanical efficiency of the cylinder is not reached; ../F5/Shift+F6/F1 confirmed shortened opening time: engine at idle + Stratified charge selected):

Unfortunately, normal functionality of MSD is not restored:

a) starting new driving session;

b) deleting the error message memory of MSD.


If the Stratified charge has indicators (as mentioned before), which are identifying the current problem, then Homogeneous mixture mode has no direct evidence of it.


That’s how to look’s data of Rough run in the current case – data from the engine with the damaged injector of cylinder No.6 (in menu ../F5/F7 cylinders are displayed in firing order, it means, 6 matches cylinder No.4):

As can be seen, cylinder No.6 (No.4 in firing order) shows increased mechanical efficiency (Stratified charge data, which can be seen in the previous image, confirm – the fuel supply of cylinderNo.6 has to be strongly decreased to normalize efficiency of cylinder No.6 – in other words, it confirms problems with cylinder No.6), but in error message memory of MSD there are error messages regarding misfires of cylinders No.4 and No.5 (because on the beckground of enriched fuel mixture of cylinder No.6 the fule mixture for cylinders No.4 and No.5 is corrected to lean to reach Homogeneous mixture inside this current bank).

Note: Rough run data are in firing order (1/5/3/6/2/4); increased efficiency: value below 0.


What to do, if in idle incorrect Rough run data are observed (even the bar of only one cylinder has a longterm difference from 0 in one “polarity”).

a) check ../F5/Shift + F6/F5, eliminate problems with cylinder(s), which are showing increased differences from 0;

b) after solving the problem: delete all group No.2 of adaptations: ../F8/F2/Shift + F9*;

c) perform initial adaptations of flywheel and banks, as described here;

d) perform driving and idle sessions (several times 5 + 5 minutes);

e) evaluate Rough run data in idle for Homogeneous mode and Stratified charge.

*if OEM NOx sensor installed, please perform Forced desulphation session BEFORE clearing of adaptations, as described here.


The situation is even more complicated because Homogeneous mixture and the Stratified charge have different algorithms, it means – data of Stratified charge can be in permissible limits, but in Homogeneous mode – outside the permissible limits (and unevenness in a Homogeneous mode in idle will not be evened out). Therefore, if Stratified charge data exceed +/-1.0 mg/stk – this situation has to be paid special attention to.

If all injectors are performing correctly, these data have to be in limits around +/-0.75 mg/stk.


Note: if the engine has problems with NOx system, the Stratified charge is not used, and algorithms for evening the idle are paralyzed. Also, algorithms for evening the idle in Homogeneous mode are disturbed, lasting disbalance between cylinders – unfortunately, it’s a typical issue. To solve this problem, at first the problems with NOx system has to be solved, old adaptations have to be deleted and new ones have to be created. Only then the shivering in idle and imminent misfires will stop.


Related entries:

Stratified charge. Idle. Part 2

MSD80 diagnostics

N53B30. When adaptations failed