"Fuel Cut" is the common term for what happens when the ECU detects what it thinks is too much air entering the engine. Under normal conditions, the car would almost never see this much air volume, so if you modify the car (say, by turning up the turbo boost) and more air is flowing in, you may reach the point where the ECU says "no more!"
When the ECU sees this level of air flow, it immediately reacts by SHUTTING OFF fuel to the engine. If you're in a low gear, it feels like you hit a wall. Even in third of fourth, it can be a pretty scary feeling, as the engine just shuts down for a second or two, then comes back online.
There are a couple of solutions to this. One is to fool the computer into thinking there is LESS air coming in than there really is. There's room for this, since the factory fuel program is so conservatively rich. You can modify the airflow sensor, use the Super AFC, or both, to reduce the airflow measurement that the ECU is seeing.
The other (more precise) way of getting around this problem is to have your ECU reprogrammed by Technomotive. See our Tip of the Week on ECU mods.
Usually we see cars exhibiting fuel cut at around 18psi of boost at normal temperatures. At colder temps, it can happen earlier, and it seems to vary from car to car as well. Note that if you're seeing fuel cut at lower, or normal, boost levels, you may have an intercooler pipe leak that is letting pressurized air escape under boost.
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