This entry is dedicated to the topic – how to work with Rough run data, how this information can help us in our work.
True though, harsh reality will introduce its corrections. I planned to describe both ISTA and INPA, but…
Let’s start with basic things: Rough run data display mechanical efficiency of each cylinder. DME, measuring the momentous speed of the flywheel, measures the efficiency of each cylinder and, knowing, in which cylinder the fuel burns in the exact moment, knows, how to calculate relative contribution (comparing to other cylinders) of a current cylinder.
Rough run data are measured in idle and in range of small RPM. It’s interesting, that INPA stops displaying Rough run data, as soon as DME confirms, that it’s not idle mode anymore, instead, ISTA (from the Main menu) continues to display data also till higher RPM (to 1500 .. 2000 RPM).
Usually DME measures time – how much times passes, while the flywheel carries out sector, dedicated to each cylinder, that’s why usually reduced (<0) Rough run data value means – flywheel has turned faster, mechanical efficiency of the cylinder is increased. I deliberately use the term “usually”, because not the developer of DME or INPA/ISTA doesn’t guarantee exactly such interpretation.
Even more – to make a situation even more complicated, it’s possible, that the numbering of cylinders doesn’t match one, we expect.
We are used to the concept, that cylinders are numbered, starting from 1st, then follows 2nd, 3rd etc. And, for example, for the “line engines” numbering is started from the front of the vehicle.
In turn, DME usually numbers cylinders according to firing order. Why? It is easier (more logical) to create all software performance.
Accordingly – the task of “arrange cylinders in the correct order on the screen” lies on diagnostics software (in our case: ISTA/INPA).
What to do in a situation, when, for example, DME is intended for use both of 4 or 6 cylinders (for example, MSD80)? ISTA reads all information regarding car’s configuration and chooses correct order for cylinders (or at least – so would the software of dealer’s level supposed to work).
INPA uses the same script for N43 and N53 series engine – the “mess” with cylinder order displaying us guaranteed – there is a menu, where the cylinder order of N43 series engine don’t matches nor firing, not placement order!
And at last – I’ve identified cases, when (obviously, by human factor/result of mistake) the cylinder order even for the N52 series engine don’t matches nor firing, not placement order!
About what is this entry?
At first – to evaluate, the performance of which cylinder is disturbed (less efficient), we have to understand (clarify), which data are displayed (smaller efficiency is an indication, increased above 0 or decreased above 0) and have to understand, how the cylinders are measured.
Every day I use INPA to analyze the performance of the engines. INPA gives much more information (several tenths of time), comparing to ISTA.
But, understanding, that INPA is not available in dealer centers, and also several diagnostic sets (ICOM) are performing only after ISTA, I decided to try out this – official – tool.
Short version – I don’t understand, how BMW AG can offer to its diagnostic specialists a toll, for which during several years very gross mistakes are not corrected? How can offer a diagnostic tool, which basic functionality doesn’t work?
For example, ISTA D, version 3.51.13, using diagnostics module of MSD80:
a) when trying to turn off the injector of cylinder No.1, menu shows, that the injector is turned off, but in reality, it’s not done;
b) trying to turn off injectors of the 2nd and 3rd cylinder – some of them are turned off, but, when trying to turn off the injectors of cylinders No.4 .. 6, the error message appears;
c) even, if the injector of any cylinder is successfully turned off, Rough run data can NOT be seen, it means, if they were chosen to display, this selection is canceled, and it’s not possible to repeatedly choose the display of Rough run data (while the injector is turned off);
d) while any of injectors is turned off, it’s not possible to exit DME menu, to choose Smoothness menu on Service section (Main menu on the top of the screen).
I have a question to BMW AG – if I cannot see Rough run data, Lambda values, and other information, while any component is triggered, so – WHAT’S the point of such triggering? What’s the point of just simply to turn off the injector? Moreover, this data displaying is turned off by intent – INPA allows to see data mentioned before if the injector of any cylinder is turned off.
Here, the screenshot of the current ISTA D version:
1. The menu states, that the injector is turned off, but the engine performs as before; as we see, possibility to exit the ECU call-up menu is turned off;
2. Error message, when trying to turn off cylinders No.4. .. 6.
Obviously, specialists of BMW AG dealer centers are using this Rough run menu… I don’t know, for what and how; obviously, the engineers of BMW AG are not using ISTA for their own needs – only in this way I can explain such fundamental errors of code and logic!
But, returning to Rough run data.
ISTA: as for this tool the turning off the switching of cylinders is not available; to find out, how the Rough run data are to interpret, we have to do the following:
a) open ECU call-up menu, choose Rough run data for displaying;
b) take off the decorative valve cover, turn off the ignition coil (remove the connector) of the 1st cylinder for short time (several seconds);
c) observe Rough run measurements for cylinder No.1 (whatever the displaying order of cylinders would be, 1st cylinder always will be a 1st cylinder of the 1st bank).
My observations show, that ISTA usually interprets the data in the following way:
a) increased mechanical efficiency: indication <0;
b) decreased mechanical efficiency: indication >0.
Attention: Rough run data, displayed by ISTA:
a) displayed in ECU call-up menu coincides with data, displayed by INPA;
b) displayed from Main menu (Service function) shows 100/256 times increased values – they can drop out min/max range (+/200 units).
Unfortunately, Rough run data of many DME versions (by efficiency 0) exceeds data, displayed in ISTA Main menu (displaying range -200 .. +200), which means – unfortunately, it’s not possible to calculate, what efficiency would correspond, for example, +/-5%.
Short conclusion – ISTA (Main menu: Vehicle management/Service function) IS NOT suitable for analysis of Rough run data.
In the image: ISTA Rough run data (ECU call-up menu).
Analysis of INPA Rough run data.
Also, INPA usually shows similar “polarity” of Rough run data – decreased efficiency of the cylinder is displayed with >0 data value.
Disconnecting the ignition coil of the 1st cylinder can see, what value INPA shows when cylinder efficiency is 0. This value can be significantly different for different versions of DME!
For example, there are versions, where 0 efficiency by INPA will be displayed around +8.0 units; there are versions, where the 0 value will correspond to +0.2.
Accordingly – it’s possible to evaluate, which value will correspond to the cylinders if they will work with, for example, +/-5% unevenness. In first case it will be: +/-0.4; in second: +/-0.01.
It’s important to make these calculations – for some software releases absolute values of Rough run data differs for even 100 (!!!) times – that’s why, when talking to Rough run, I never mention absolute values (without connection to 0 efficiency they will not give any information).
When the “polarity” and scale of Rough run data are clear, we have to identify, in what order cylinders are numbered. If current INPA loader is used for the first time, it is useful to check the sequence of ALL cylinders, one by one turning off (for several seconds) their ignition coils and observing Rough run data.
Of course, if corresponding INPA loader is used repeatedly, it’s no need to check the cylinder order – it’s enough to check your notes or recall your memory.
Attention: INPA offers (and usually this menu works, unlike ISTA) turning off of cylinders (injectors). When the cylinder displaying order (for current loader) on the screen is known, its possible to check, in which order the cylinders are displayed in cylinder switch-off menu. The procedure is simple – again, one by one, turn off the cylinders (using INPA menu) and by Rough run data check, in what order they are switched off. And again it’s recommended to make notes – they will be useful in the next diagnostics sessions.
When the basic things are clear:
a) “polarity” of Rough run data;
b) values of Rough run data, which matches efficiency 0;
c) displaying the order of cylinders in Rough run menu INPA/ISTA;
d) displaying order of cylinders in injector turning-off menu (if it works);
we can evaluate the mechanical efficiency of each cylinder!
Even more – we can try to find a leaking injector, turning off the engines one by one and evaluating Lambda, which is reported by wide-band Lambda probes – more information here.
Turning off the first cylinder, it’s Rough run data showed +7.0 units. Conclusions:
a) decreased efficiency: increased (>0) Rough run value;
b) +7.0 units corresponds to 0 value; +/-5% coridor corresponds to around +/-0.35 units;
c) checking, it was found, that data is displayed by firing order (1/5/3/6/2/4).
As we see, for example:
a) efficiency of 2nd cylinder (by firing order) = 5th cylinder (by placement) is around -13%;
b) efficiency of 4nd cylinder (by firing order) = 6th cylinder (by placement) is around +5%;
c) efficiency of 6nd cylinder (by firing order) = 4th cylinder (by placement) is around +10%.
Additionally – exactly the Lambda probe of 2nd bank shows rich mixture (U<2.00V = Lambda around 0.99) – obviously, exactly the 2nd bank has some problems with fuel distribution between cylinders.
I can say from experience: around +/-5% efficiency jittering is normal to the used engine. This is a small difference between cylinder efficiency and subjectively the engine works very evenly (no permanent vibration observed).
Around +/-5% is the threshold, which as permanent (not compensated) difference is acceptable to the engine with Valvetronic (DME of MSD80 type works slightly different – they try achieve total compensation of the mutual efficiency of cylinders – for these DME Rough run data regularly change “polarity” – it means, they are inclined to, if DME works in full functionality mode).
Note: in the bottom part of the INPA menu the status of flywheel adaptations is visible. In INPA Rough run menu, learnbit (Status: Segmentadaption) of flywheel adaptations has to be colored – only then Rough run data of cylinders will show correct values! If the learnbit is not colored, perform braking with an engine in overrun mode (4st gear from 100 .. 110 km/h) for at least 5 seconds – till learnbit gets colored.
ISTA doesn’t show adaptation status of the flywheel – unfortunately, unadapted flywheel could be one of the reasons, why ISTA shows incorrect Rough run data.