There are times that the PCM may be looking up a certain operating parameter from the memory right at the very instant that the chip calibration is changed. It doesn't really happen that often, surprisingly. It's not going to hurt anything when it happens, but it does happen occasionally. The newer trucks are more prone to it than the older ones only because there are far more things going on in at any given time with the newer ones. Consequently, if there does happen to be an interruption in the data fetching, the PCM says "What the ****?" and shuts down. Sometimes, if it's a recoverable error, the truck will simply hiccup and be on it's merry way. Other times, the PCM will not allow a quick reboot and shut the truck off completely. This is why it's better to switch the positions on the chip while coasting....there are very few things "going on" inside the PCM on a deceleration event.
Keep on truckin'!
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Tuning, PCM flashing, and burning chips for 7.3s since 2008. Repairing all aspects of 7.3L Powerstrokes for 25 years.
Eight 7.3L PSDs in the driveway including a 1994 Crown Vic and 1973 F100/2002 F350. Looking for the next victim.
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