[Richard L]

Failsafe detection is instant but not much good in practice due to inherent spiking of the flow in a dynamic environment. This will result in incessant boost cut.

The HFS-3 has inbuild low-pass filter to arrest those spikes, use the FS-DL trimmer to delay the onset of boost drop. Heavier filtering results in slower reaction time. This trimmer can be set between 0.1s to 0.6s, default is ~0.4s from factory.

You can choose to have a faster reaction time but you have to widen the failsafe window trimmer settings (WL and WH). The width of the window is also governed by the start of injection.

Boost drop is the most effective. But you can use the second failsafe option - Map switching. This channel is originally designed for third party ECU with the ability to switch ignition or fuel map upon receiving a failsafe signal from the HFS3.

As you have the factory DME, you might be able to inject a voltage into the air temperture sensor of engine temperature to force the DME to alter fuel or ignition map on the fly because it sees abnormal temperatures readings.