combustion sensors/burn times

I work on G3606 that drive gas compressors. Most of our units are in the 12000-15000 hr range. Lately, we have had issues with burn times. We get a "Combustion Data intermittent" code. I do not remember the code number but can provide it on Monday. When watching the burn times, we notice a lazy burn time usually on whichever Cyl is noted in the fault. When watching the unfiltered burn times, we see **** flash on that cyl and sometimes on other cylinders as well. What does the **** mean? When watching with ET, it will show "abnormal data". Sometimes replacing the combustion sensor has helped but other times it does not seem to. I was more interested in the cause of the stars (****).


Also along the same issue, when we have a unit start cold (hasn't ran in 4 or more hours but has hot start), we will see all of the cyls showing these stars and it is noticeable that the engine is not running correctly. Do those stars indicate a misfire possibly?