The most efficient option for evaluating the misfire counters is the average misfire data of the existing session and last sessions, found at the end of the ODB Mode 6 menu. Read here about how to interpret these data.
ISTA offers (if/when offers) one of two types of counters: cumulative (counters, which indicate the total number of misfires in each cylinder) – these data are available for some older F series vehicles (typically: with Siemens DME) and the short-term event indicators (for example, B series engines; Bosch DME).
In this entry – regarding lifetime/cumulative counters.
Whether you see these counters with ISTA or any App, the interpretation of the data is the same.
These misfire counters count all misfires of each cylinder since its “beginning of life”. Counting starts with the deletion of the adaptations. When adaptations are deleted, these counters are reset.
Nuances, which you should keep in mind:
a. Even if you deleted the adaptations a little while ago (and made sure that these misfire counters are 0), the absolute values of these counters are not the correct data! There are several reasons. First – directly after deleting the adaptations, the fuel mixture in cylinders is not correct/accurate (DME hasn’t created new adaptations); accordingly – in some or even in all cylinders, the misfire density can be (and typically is) increased. Second – uneven roads too (potholes, on the gravel road – pebbles, rocks) will provoke the identification of fake misfires. Third – Bosch DME has problems with the identification of misfires in idle (due to principle, how these misfires are identified. Patent war between Siemens and Bosch). Accordingly, Bosch uses all types of trickery to find the culprit in idle too. One of the trickeries – during the warm-up phase (first minute after the start) of the CO catalytic converter, use the Siemens algorithms, after – when not able to identify the actual culprit, continue to increase the misfire counter for the cylinder, which misfired in the warm-up phase.
b. These counters should be evaluated in the following way – read their values before and after the driving session and calculate the delta for each cylinder. In such a way, you will get the misfire data of the last session.
c. Some misfires in each cylinder – it is normal! Look for the “leader” between cylinders. The solution to the problems starts exactly with the “leader” of misfires! Remember – if the car has a manual gearbox, misfire counters can create significantly increased values in all cylinders. Actually, a misfire (in some cylinders in random order) is identified each time the gear is switched (especially relevant for B series engines). What to do in this situation, read here.
d. Try to provoke the car, especially in the most unfavorable mode – exactly when you sense the misfires. Low RPM and large load? Ensure that the engine runs exactly in this mode! Allow it to misfire! Parallelly, control main parameters: Lambda value; Integrator(s), if they are available. For N43/N53 series engines, Lambda allows the detection of the injection mode (Homogenous/Homogenous lean/Stratified charge) – which makes diagnostics much easier.
e. If the Expert mode of ISTA is available (newest F series vehicles and G series cars), use it! Here, on the same menu, you will see both misfire events and the performance of each cylinder in real-time.
f. The most popular culprits for the misfires are ignition coils and spark plugs. Replace the ignition coils regularly! If you are basically driving in the city mode, regularly clean the spark plugs from carbon residues (Service procedure in ISTA, available for B series engines). Use only OEM ignition coils and the exact model intended for the exact engine! Don’t experiment with the “sport” ignition coils or “better” models.
