How to act:
After driving session (do not switch off the engine)
- Plug ELM327 adapter into OBD socket
- Start diagnostics software (for example: Touch Scan or Scan Master ELM)
- Open OBD mode 6 (‘On-board monitoring’ for Touch Scan; ‘Monitored test results’ for Scan Master ELM)
Disclaimer: as usually – no information from the manufacturer regarding algorithms, all information gathered from analysis and observations.
Note: this feature is available for the following engines: N43/N53; N54; N55, etc.
Each cylinder has misfire counter outputs, and they contain two kinds of information:
a) counter of misfires for the actual session;
b) counter of misfires during sessions.
The counter of misfires for an actual session is zeroed, when the driving session is started.
Counter of misfires during sessions is calculated as following: long_count – 1 + 0,1 * act_count, where act_count is count of misfires for previous actual session, but long_count is counter during sessions.
(some resources describe relevance: 0,9 * long_count + 0,1 * act_count).
Sample: the counter of the actual session is 33, the counter during sessions is 2. Starting new driving session, the counter of an actual driving session will 0 (it is being zeroed), but counter during sessions will be: 2 – 1 + 33 * 0,1 = 4.
The image: how the counters of an actual session and during sessions are placed.
For N53 series engine: last 12 lines;
For N43 series engine: last 8 lines.
Interpreting the results:
- Misfire counters during sessions should be 0. If some of these counters are different from 0: corresponding cylinder has problems with ignition.
- Misfire counter of the actual session should be close to 0. Acceptable values: up to 5 during the long driving session (more than an hour).
Exception: some MSD80 software releases are very sensitive to the uneven road. Misfire counters may have increased values after driving on the uneven road.
How to clear misfire counters.
The counters can be deleted in the following way:
a) engine OFF;
b) engine ON.
Repeat the procedure, until all counters of misfires during sessions become 0 (the counters will decrease with speed – 1, till the value of 0 will be reached).
When long-term and short-term misfire counters are observed, we have made the decision, what to do.
In this entry – possible scenarios.
I assume the basic problems of the engine performance are repaired – DME has no error messages, recorded in the error message memory; adaptations and other live data indicate correct values. But the performance of the engine is uneven, and misfire counters are checked: they indicate problems with fuel ignition.
If an increased number of misfires is indicated by all or almost all cylinders:
1. check the spark plugs. For engines of the new generation (direct injection), the spark plugs have to be replaced quite often. for example, for N43/N53 engines, the spark plugs serve not more than 20 .. 30’000 km;
2. if the spark plugs are installed recently, and the engine restored the ability to work in Stratified charge mode recently (and problems started directly after restoring Stratified charge) – check the installed spark plugs! In their catalog, Bosch has mistakenly indicated, that they manufacture spark plugs, which can be used in N43/N53 series engines. Also, NGK in their catalog has indicated inappropriate spark plugs (indicated, that spark plugs, which are suitable for N52 series engines, can be used ion N43/N53 series engines). Use only OEM codes of spark plugs, don’t buy cheap alternatives!
3. if the engine has been operated with worn out spark plugs for a long time (their air gap – enlargened), also ignition coils can be already damaged – in this scenario (if the air gap of the spark plug is increased), they have much higher loads.
If one/two cylinders indicate an increased number of misfires:
1. start the elimination of problems with the cylinder, which indicates the largest problems. Keep in mind – in case of misfires of one cylinder the performance of the engine can be such uneven, that the DME self-diagnostics sometimes falsely indicates also some “connected” cylinder. The connected cylinder is a cylinder, which follows the damaged cylinder (the one, who truly has misfires) by firing order. For example, for N53 series engine in case of misfires of the 5-th cylinder, false misfires in cylinder No.3 can be indicated (because the firing order is 1/5/3/6/2/4 – it means, that cylinder No.3 ignites the fuel directly after cylinder No.5);
2. if similar (it means, the misfire counters are different, but not so significant, that we could say – the problems are only in one cylinder) misfire number is indicated by two “following” cylinders (by firing order), start the elimination of the problem with first one by firing order. For example, if similar problems are detected for 2-nd and 6-th cylinders, start the elimination with cylinder No.6 (because the firing order is 1/5/3/6/2/4, and the 6-the cylinder is “before” the 2-nd cylinder);
3. when the cylinder, who is the guiltiest, is chosen, take off the decorative cover of the engine and perform activities, described below. Of course, you can follow the suggestions of dealer or ISTA – replace all spark plugs, ignition coils, injectors, but – is one damaged spark plug/ignition coil worth to change 11 or 17 good working elements and unreasonably spend more than EUR 2000? In my opinion – it’s not.
Possible causes of an increased number of misfires:
1. spark plug;
2 ignition coil;
I eject damages of the engine – unclosing of the valves, high wear of the engine block, etc. Such problems can be indicated by checking the compression of cylinders. In addition – in case of such damages, the adaptations of the injector of the current cylinder and incorrect mechanical efficiency of the exact cylinder should be present.
How to act:
1. For the engine with 6 cylinders – replace the ignition coil of the “damaged” cylinder with the ignition coil of next cylinder (by placement). For example, if the problem is in cylinder No.5, replace its ignition coil with one of cylinder No.4 or No.6. Why exactly with the next cylinder? Because the next cylinder (by placement) will not be the connected one, it means, it will not be next by firing order. For an engine with 4 cylinders – choose cylinder, which is not next by firing order. For example, if the problem is in cylinder No.3, DON’T choose the cylinder No.4 for replacement (because the firing order is 1/3/4/2, and the 4-th cylinder is next after cylinder No.3 by firing order);
2. perform several at least 10 .. 15 minutes long driving sessions. Read the misfire counters repeatedly. Check, if the problem is still in the same cylinder, or it has “traveled” the the “new” cylinder. Remember, that long-term counters contain information regarding many (even more than 10) last driving sessions. For this reason, the short-term counters have to be checked carefully. Long-term counters will show long-term tendencies. If the long-term counter of the “old” cylinder has reduced, but for the “new” cylinder – increased: there is no doubt – the cause of the problem is found;
3. if the replacement of the ignition coil didn’t help, next step – switch the spark plugs with the next cylinder by placement. Further actions – the same as described above;
4. if the replacement of spark plugs also won’t help, switch the injector with one of the next cylinders. Also this time – act as described before. To spare your time – don’t encode the injectors and don’t perform other service procedures (re-adaptation of the engine). Even, if the fuel mixture won’t be perfect, it can not be the cause for many misfires.
One of three steps, mentioned before, will allow identifying the damaged part for sure. When it’s detected and replaced, perform some more driving sessions, to make sure, that the engine works correctly. If any cylinder still has misfire problems – repeat the test procedure for this current cylinder, as described before.
After solving the misfire problems, don’t forget to re-adapt the engine!