Misfire counters. Part 2

In this part, I will compile information, which is worth a closer look. Thank you to many participants of the BMW commune for questions!

 

Several times I encountered information, reported by BMW users: the shivering of the engine (also in idle, when it’s easier for DME to detect the misfires) can be felt, but misfire counters are 0.

We have to keep in mind several nuances:

a) of course, misfire counters have to be checked after driving session, NOT TURNING off the engine. If the engine will be switched off, misfire counters of the actual driving session will be deleted, even long-term counters, which are recorded in the memory, can give a reading of 0 misfires;

b) even for a perfectly working engine, in a longer period of time DME counts some events of a misfire. It can happen because of uneven roads or swifter change of driving conditions. Even, if not other obstacles, we have to keep in mind – each cycle of fuel ignition is unique, every time fuel burns differently. From several million times, when the fuel is burned, there, for sure, will be some time, which will be more different, and DME can indicate it as a misfire.

 

Misfire counters can indicate 0 in all conditions in the following cases:

a) the software of DME has been changed. Sometimes, when ”specialists” are not able to find a real cause of the DME error messages of misfires (for example, an improper model of spark plugs installed, problems with injectors, NOx system; not re-adapted engine, etc.), “masters” prefer to turn off the misfire-detecting algorithms and deleting the appropriate error message from the error message map;

b) OBD equipment doesn’t read misfire counters of the exact DME, or don’t support OBD mode 6 at all.

 

If still (after driving session, not turning off the engine) all misfire counters are 0, the following test has to be performed:

a) take off the decorative cover of the engine;

b) turn on the engine;

c) for several seconds, disconnect the connector of the ignition coil of any cylinder.

 

Check the misfire counters (not turning off the engine). The counters of the actual session of the appropriate cylinder has to be in several tenths or even hundreds of units.

 

Turn off and turn on again the engine. The misfire counters of previously “damaged” cylinder now have to be 0, but the intersection counter has to be 1/10 of the previously detected number of misfire cases (for example 5, if before 53 events of misfires have been identified).

.

If any group (or both) don’t indicate a misfire, it’s clear, that either DME or OBD equipment has problems with detection or indication of misfires.

The error message of DME has to contain the error messages regarding misfire of this cylinder and also it’s disconnection (due to group misfires, if the cylinder was switched off by DME). If no such error messages exist (at least – first one) – restore the DME software and encoding/configuration to one, offered by the manufacturer.