I came upon this problem of the 6th cylinder by observing completely different oddities in the performance of this engine.
Yes, directly after the purchase, I noticed that not all cylinders work perfectly. Some sort of idle problems were fixed by the Integration upgrade of the Year 2023. Something I “wrote off” on the Bosch management system – creations of this company have long been slightly “simpler” (excuse my directness). As long as the car runs without error messages, shivering, and other critical problems, it has to be enjoyed.
Initial oddities, which I noticed – registered, but not confirmed, error message regarding the performance of the CO catalytic converter. Yes, the mileage was close to 300.000 km, many will say – what would you expect? It had to be replaced a long time ago! Bet I had a counterargument: the error message was registered by Lambda 1.07. The control probe indication of around 0.17V in such a situation is correct! If there is an air leftover, the CO catalytic converter in no way can burn excess air! Ok, let’s perform the cleaning of the spark plugs from the carbon (assuming that the misfires appeared due to their contamination). After cleaning the spark plugs, the situation seemed to improve slightly, and still, analysis of the Lambda probe indications after some time indicated that the whole exhaust is saturated with oxygen. Where and why is there excess air in the exhaust?
In idle, the engine performs perfectly.
But, as the problem with the excess air was detected on the go, the performance of the cylinders should be checked on the go, too. What is that?
Red curve – position of the accelerator pedal: around 20 .. 30% (starting with the 210th to 217th seconds).
The engine works in the naturally aspirated mode. And the efficiency of cylinder No.6 (light blue curve) reduced by 10 .. 15%!
Why so?
Pressing the accelerator pedal a bit more:
We see that the Twin Scroll turbo starts its work – the cylinders are “parted” into two groups. The performance of the first group (1st to 3rd cylinder) is larger, and the performance of the second group (4th to 6th) is lower. But again, in the range of the second group, Cylinder No.6 is very lazy!
What could be the reasons for the laziness of the 6th cylinder?
Let’s start with things that could not be the cause of this problem:
a. Valvetronic. It can be clearly seen that the problem increases when the required torque increases. The larger the required torque, the smaller the impact of the Valvetronic. Without options – dismissed;
b. Consequences of the knocking, as a result of which the DME has adjusted the ignition to extremely late?
In all cylinders, the knocking indicators are identical. If there were a problem, I would expect (at least) short-term increased indicators, which are compensated by short-term Ignition adaptation for this cylinder (even assuming that long-term adaptations have significantly modified the ignition map for the 6th cylinder). Let’s rule out ignition problems.
c. Twin Scroll turbo impact? Yes, such turbo loads the engine asymmetrically. But the cylinders No.4 and No.6 are loaded on one turbo unit air duct;
d. configuration of the exhaust manifold. Yes, for the 6th cylinder, there is a different exhaust manifold. But then the 1st cylinder should have similar problems! In addition, the problem can be seen by low RPM, by low required torque (and low flow of the exhaust gases in the exhaust system). No, this is ruled out, too;
e. mechanical damage of the cylinder (problems with the rings, scratches in the block walls); burned-out valves? No, dismissed: idle (and increased RPM without load) is perfect, peculiarity observed for a longer time – it is stable, not progressing. The problem increases when the RPM increases (it is not typical for mechanical problems, because the gases have a shorter time to leak). Pressure in the crankcase is correct; all fuel adaptations are correct. Dismissed.
Let’s move to the reasons, what could be the cause of this problem:
a. incorrect adaptations (misfires would be ones to blame, caused by problems with the overheating ignition coil);
b. the cylinder lacks air;
c. The cylinder lacks fuel.
I readapted the engine. Drove 1000+km, regularly switched on the cruise control, for DME to make adaptation work easier. Yes, it is possible that in separate segments the problem was slightly reducing, but absolutely definitely did not disappear.
Can the cylinder lack air? The problem stayed (and became more pronounced) in the form of a large required torque. In this mode, Valvetronic in no way impacts the inlet. The inlet manifold is common for all cylinders. Dismissed. Clogged intake tract?
I checked how the PCV is created – correct, oil steam is fed into the inlet, closer to the 1st cylinder. Is the inlet manifold placed slightly slantwise, or are liquid fractions leaking to the side of the inlet valves of the 6th cylinder? But the problem is also due to low RPM, low required torque! No, the clogged inlet track is dismissed, too!
The only reason: the cylinder lacks fuel.
In the normal situation, DME should be able to compensate for the flow rate differences of the injector. For this cause, the following adaptation types are available:
a. chemical efficiency tests (description here);
b. mechanical efficiency tests (these measurements are supposedly not covered by the Siemens patent and could be performed based on the crankshaft sensor readings).
Off topic. For N series engines, mechanical efficiency tests were performed only in idle (until MSD80/81), till 1500RPM (MSD87). At higher RPMs, only chemical efficiency tests were available. For B-series engines, an adapted flywheel gives correct/exact information regarding the mechanical efficiency of cylinders until 3200RPM.
What could be the cause? There are not many options – injector! But if the injector is not damaged, DME should be able to fix the previously mentioned efficiency problem. In what situation would DME not be able to “fix” the issue? For example, if the injector has poor atomization. In such a situation, DME (when performing chemical tests) would see that the injected fuel amount is correct, but still, the cylinder is “lazy”.
Obviously, the poor atomization is to blame. And what coincidence – again cylinder No.6! I was ready to order six new injectors (taking into account that the existing ones have served close to 400.000km), but then I thought – I do have diagnostic data of many B58! Let’s see how other cares are doing!
Here, for example, a G series car:
And here, one more:
And more, and more…
How is that possible? All the cars whose data I look at, ALL have problems with the 6th cylinder?
And a very short remark – yes, all cars have been readapted, the flywheel is adapted, Overrun mode indicates its correct performance.
At this moment, I understood that it makes no sense to buy new injectors! My only explanation – there are serious troubles with the software!
