ISX15 CM2250SN surging whilst at speed/load

[Rawze]

Anything much above abut 248kpa on that boost setting is going to shorten engine life over time. = running too lean and eventually cracked head or blown head gasket prematurely.

Below about 233kpa is under-boosting and is very hard on the turbo with excessive heat in the exhaust.

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stop guessing blindly...
If the power is shifting, and its suspected that anything whatsoever in the programming at all is contributing towards it, then use Calterm to monitor what is happening in the engine. Monitor specially the the 'CBL_Fuel_state' parameter and others related to it. This will tell you exactly what is happening and why.
use this screen file + some desktop recording software (like OBS studio, etc.) to record what is going on on a test drive ...
ref: https://rawze.com/forums/showthread.php?...6#pid28636

Post a link to a desktop recording of when its running right .. and then transitioning to acting up or screen shots) again when its acting up via that CT session screen I linked to. I can translate the numbers into what its doing.

lastly.. are these engine deleted?.. (de-mandated)?. if so then copy the program out of the ecm and e-mail it to me for a review of what some yahoo did in there, as more than 90%+ of all delete programming out there is half-aarssed and harmful to the engine.