The Fuel Cut Defeater is another simple "interceptor" design. It modifies the signal from the engine’s MAP (Manifold Absolute Pressure) sensor and stops it from exceeding a particular level before feeding to the ECU. Therefore, the ECU does not sense the over-boost condition brought about by the Variable Boost Control and hence does not cut the fuel supply via the injectors.

The circuit is built on a small PC board and there are just four external connections: ie, +12V, 0V (chassis), MAP sensor and the output to the ECU.

The circuit (Fig.1) is very simple and is based on a TL072 dual FET-input op amp package. IC1a is connected as a unity gain buffer (with its output connected directly to the inverting input) so that there is negligible loading of the MAP sensor signal.

Input protection for IC1a is provided by the series 10kW resistor and by diodes D1 & D2 which clamp any large signal transients.