This time – regarding data, available in the ISTA/Expert mode. I will start the review with the first menu: analysis of Rough run data.
Here, how the Rough run data look alike:
Legend:
I have to admit that this menu is relatively “usable”. Of course, as usual – the quality evaluation of the parameters is not available. What are deviations from the ideal allowed? What indicates serious problems? BMW does not say to us. We can only rely on experience.
Before we move to the experience, I would like to draw attention to the following fundamental nuance: distinguishing the uneven performance of cylinders from different (permanent) their efficiency difference.
- Different (remaining) efficiency of cylinders:
Unit of cylinder mechanical efficiency measurement: scale 2.
As we see, the red and yellow curves are fluctuating around 0.0;
Both blue curves are fluctuating around +3.0;
Green and grey curves are fluctuating around -4.0.
Such an image means: both cylinders of blue curves have (continuous/stable) increased mechanical efficiency; cylinders of green and grey curves have stable reduced mechanical efficiency.
According to the legend of the curves:
a. The efficiency of cylinder No. 1 and No.6 is the largest;
b. The efficiency of cylinders No.3 and No.4 is average;
c. The efficiency of cylinders No. 2 and No.5 is the smallest.
Why does such a situation form? Obviously, cylinders No.1 and No.6 have the best supply of air and fuel. The situation of No.3 and No.4 is slightly worse, but cylinders No.2 and No.5 don’t have either fuel or air. What exactly – this is already the next step in the diagnostics.
Such performance of the cylinder causes the “diesel car feeling” – permanent vibration. Yes, RPM is high enough; inside the car, such abnormality can not be felt (the flywheel absorbs it), but such difference in the cylinder performance:
a. gives increased load on the CO catalytic converters and damages them;
b. reduces max torque of the engine;
c. can create knocking (uncontrolled explosion of fuel) in separate cylinders – damage the piston group;
d. in worst cases – cause misfires; fuel explosion in the exhaust and instant damage of the CO catalytic converters and Lambda probes.
Causes of the defect:
a. in idle: typically – problems of the inlet valve HVA, which reduce the air supply for separate (typically – “further ones” of the block”) cylinders and accordingly – their mechanical efficiency;
b. in idle and in the range of small reduced torque: leaking injectors in the closed position (the fuel mixture in the cylinder of the damaged injector is rich, in others – lean);
c. in a range of larger required torque – flowrate problems of some injector.
Notes. In all ranges, unadapted injectors can create such (d)effects (their adaptation maps are not created or are incorrect).
- Uneven performance of cylinders
The fundamental difference from the previous image – curves of the cylinder performance are zigzags, jumps “up/down”. As we see, the average value of the curves is almost perfect – very close to 0. Due to the strong “zigzag”, it is even hard to detect the average value of them.
Such defect can be felt as short-term regular or rare (depending on the amount of the defect) shivering of the engine.
Cause of the defect – misfires or unregular bad fuel burning. Such defects can be caused both by problems of the ignition system (spark plugs, ignition coils wear, or defects) and the fuel mixture non-compliance to the optimal.
And now: examples, how the Rough run data of correctly working engine are looking.
Idle:
Low required torque (20 .. 40 Nm; accelerator position around 10%):
Average required torque (pedal position around 25%):
Larger required torque (accelerator pedal position around 45%):
If you are interested in the quality parameters of this menu, do as “usual”:
a. open the Rough run menu;
b. turn off the ignition coil of some cylinder for a running engine.
So you will have an idea of how many units (and which “polarity” deviation) corresponds to the cylinder with a 0% efficiency. Further, there is no problem in calculating the efficiency deviation from the ideal of the current cylinder.
