Fuel Cuts

Cars affected: Evo 1-7

Symptom:

A very sudden de-acceleration due to the fuel being cut to the injectors, similar to your foot slipping off the accelerator except it will recover almost immediately. It occurs if over boost is detected while accelerating hard (common at roughly 4000rpm in 2nd, 3rd or 4th gear but possible at other rpm and gears). Also it is more common if the outside air temperature is colder.

Problem and cure:

Fuel Cuts are the Engine Management.s way of stopping serious over boost situations occurring. Instead of detecting the actual boost pressure the ECU (Electronic Control Unit) uses information from the Air Flow meter to work out the boost pressure. The ECU will cut the fuel at roughly 1.3 bar boost pressure (18.8 PSI) on the Evo 6 (approximately 1.5 bar on the Evo 7) but the specific cut point is dependant on atmospheric conditions at the time so it will not be the same from car to car. Fuel cuts are more likely to occur in winter as the air is colder and therefore more dense. Early Evo models may have a lower cut point that is in relation to their standard boost pressure level setting. Fuel cuts commonly occur after fitting an upgraded aftermarket induction kit and/or exhaust due to the increased air flow they create but fuel cuts have occurred on standard cars before. It is also possible for fuel cuts to occur due to a faulty Wastegate Actuator but it is not that common (see elsewhere). Do not live with fuel cuts! The sudden cutting of the fuel sends a shock through the engine and drivetrain which in itself can be harmful. You can temporarily 'drive around' fuel cuts by avoiding using full acceleration or if very worried keeping below 4000rpm at all times (as if you were running in the engine). The cure for fuel cuts depend on what is causing it and also what you intend to do with your car. If you believe the over boost is due to any upgraded parts that have been fitted then the boost level can be dropped fairly easily by a manual alteration to the Boost Control system, although dropping the boost obviously partially defeats the object of fitting performance parts. If you intend to modify your car further then you will require an upgrade to the Engine Management to either eliminate the cut point or .work around. it. It is not recommended that you use a .Fuel Cut Defenser. as they tell the ECU that the fuel cut point has not been reached by electronically reducing the air flow signal and this can lead to a lean mixture as the ECU will reduce the fuelling to suit. If you are having problems with fuel cuts then consult a qualified garage/mechanic that knows about Evos and also let them know what you intend to do with the car in future.

Approximate cost of repair:

Depends on the fault.

Adjusting the boost level down slightly will take 30 minutes with no parts required.

A new Wastegate Actuator is approximately £200 inclusive (plus fitting approx. 1 hour)