Today’s patient – very unattended E63 with N62 series engine. The current owner has purchased the car without any diagnostics – hoping, that everything will be just fine. Unfortunately, he just barely made it to the service.
This car was chosen as a diagnostics example, because when starting the engine, it shivered, in the error message memory – ten error messages. A “normal” person would get confused easily – with what to start the repair? Many parameters are outside the allowed corridors! So I will explain, what I did – hopefully, it will be useful.
So, when opening the error message list, we see:
As you see, there are error messages regarding misfires of all cylinders, fuel mixture, the ventilation system of the fuel tank, efficiency of the catalytic converter.
When starting the engine, it shivered very strongly, as if with additional shake-up time by time.
To find the cause of the vibration, I opened the menu of cylinder’s mechanical efficiency.
Here, the cause of vibration. Cylinder No.6 – turned off, its mechanical efficiency is 0.
Note: Bosch DME in this menu usually displays the sequence of cylinders in the placement order, but – I still suggest to make sure about it!
How to do that? Read in the description of the Rough run menu (here)!
For a moment I opened the menu of the Lambda probes, the voltage of the wideband probe of the 2-nd bank was around 2.10V (by Lambda 1.00 the voltage is 1.50V) – the mixture is lean: 100% confirmation, that the cylinder (its injector) is disconnected.
What to do in such – completely “abnormal” – situation.
At first, we have to achieve, that the engine runs with all cylinders. Only then it makes sense to see further. If DME has no defects (internal failure), then – when starting a new driving session (sleep mode is not necessary, it’s enough to turn off and on the engine), DME will restore (will try to restore) the performance of all cylinders. Of course, if a group misfires will follow – the damaged cylinder will be disconnected, but, if the situation is not critical: all cylinders will stay on at least for a moment.
After repeated starting, the vibration has been reduced, but irregular shivering of the engine was still observed. When opening the Rough run menu, I made sure, that all cylinders are working. Yes, indeed, also the 6-th cylinder was running. These were good news.
Note: if the performance of the engine doesn’t restore after the restart, start with the ignition components: ignition coil and the spark plug. For the engines of direct injection, this defect can be caused by an injector (true thou, relatively rarer), but for the “regular” engines such defect of the injector isn’t observed.
When all cylinders are running, I move to the next stage – evaluate the fuel mixture. I’m opening the Lambda probe menu:
Wideband probes of both banks indicate a correct fuel mixture (by Lambda 1.00, Bosch DME wideband probes indicate 1.50V). This is a very important indicator. I will explain – why.
As we see in the error message list, there are error messages regarding misfires of practically all cylinders. Misfires can be caused by weared-out spark plugs, damaged coils, incorrect fuel mixture.
In this case – the fuel mixture is correct, at the same time the engine shivers irregularly: misfires are observed.
If there are misfires in case of a correct fuel mixture – the cause of the problem are the ignition coils or/and spark plugs. One of the directions for repair is clear now.
But this menu gave some more important information. Pay attention to the offset type LTFT:
As we see, in idle the DME has significantly increased the fuel consumption to reach a correct fuel mixture.
This problem is typical in the following cases:
a) lowered fuel pressure;
b) air suction in the inlet manifold.
Taking into account, that the DME has recorded the error messages also regarding the ventilation system of the fuel tank, with 99% probability, the air suction problem is one to blame.
Here, also the second direction of the repairs is clear – the smoke test have to be performed and also the airtightness problem of the inlet manifold has to be eliminated.
For engines, equipped with Valvetronic, I perform one more very important check: the ability of the DME to correct the mechanical efficiency of cylinders in idle (when Valvetronic is enabled).
This time after restoring the performance of all cylinders, I was confronted with a slight problem: DME stubbornly refused to turn on the Valvetronic:
As you see, the elevation, required (and also executed) by inlet valves, is around 9.5 mm. The restart and the deleting of the error messages didn’t help. The warming up of the engine till work temperature and waiting of 40+ seconds during the next working sessions didn’t help either. Obviously, DME considered, that the damages, identified before, are too serious. There was only one argument left: sleep mode. Ignition off, the key – out. Let’s wait till the lighting of Start/Stop button will disappear.
After Sleep mode there is good news: the Valvetronic is finally switched on!
And at this moment – I switch to Rough run menu.
Data indicate relatively good picture. Mechanical efficiency in all cylinders is “wavy”, but at the same time – no one of cylinders was strongly behind, indications of all cylinders were fluctuating around 0.
These are good news. In case, if any of the cylinders get extremely “lazy” (its bar indicates the positive value, which overreaches 5 .. 10% of completely turned off cylinder), a typical cause: HVA of the inlet has a freelance. HVA problems, instead, are caused due to unchanged oil. In the case of HVA problems, the repair is relatively expensive – the oiling channels of the engine have to be cleaned, the inlet HVA (or even better – all HVA’s) have to be replaced.
And at this moment it’s worth to check the fuel mixture once again:
As we see, the integrators are 1.25 or +25%, it means, that DME has suddenly increased the amount of the fuel mixture for 25%. Not taking into account, the fuel mixture is strongly lean (the voltage of the wideband probes are strongly above 1.50V).
And more – we see, that the offset type LTFT is 0, which means: DME has not confirmed the offset type adaptations (as we can see from the first image of this menu), which are so important.
Summary. Repair directions:
a) ignition coils and spark plugs. In case, if the spark plugs are very worn, the ignition coils also have to be replaced, because the spark plugs with an increased air gap damage the ignition coils;
b) smoke test for the inlet manifold, elimination of the air suction.
After these repairs: re-adaptation of the engine. Then – repeated diagnostics (evaluation of the fuel adaptations).
Hopefully, the next phase of the repair will be limited with a replacement of the thermostat and the error messages regarding the catalytic converter are recorded due to incorrect performance of cylinder.
Note: the error messages regarding the performance of the catalytic converter can be recorded due to incorrect fuel pressure (typically: lean ixture), misfires of cylinders, the incorrect split of the fuel mixture between cylinders. Therefore before blaming the catalytic converters, the correct performance of other hubs has to be restored.