Fuel Level Switch
The IST includes a fuel level switch to detect impending supply issues.  Under normal operation (IST full), the switch is closed.  If the fuel in the IST falls below approx. 20%, the float will fall and the switch opens.  This function can be used to initiate a variety of safety precautions.  This setup will provide advance warning that will allow you to save your engine.  The following alternatives are suggestions; the car builder has full latitude to implement in any form:

Alt 1:  Programmable Engine Control Unit (ECU) -- Active Safety Feature

If the ECU receives a low fuel level signal from the IST, it will revert to "safe mode", where the following actions are taken to avoid engine damage:
  • Decrease boost
  • Retard ignition timing



Alt. 2:  Electronic Boost Controller (EBC) -- Active Safety Feature

The EBC controls boost normally, with the Boost signal passing through the relay.   A low fuel level signal from the IST will open the relay, interrupting the Boost signal.  Boost will revert to the minimum level, as determined by the physical spring in the Wastegate. 


Alt. 3:  Warning Enunciation -- Passive Safety Feature

If it isn't feasible to automatically control engine operation, as in Alts. 1 and 2, a passive safety feature such as a warning light or buzzer can be implemented.  This option requires driver attentiveness and quick intervention, which makes it less desirable.