Overrun Fuel Cut (or OFC for short) is a method used by some OEM ECUs to turn off fuel injection under certain conditions - such as rolling down hill with the throttle closed (ie under engine braking.) It can help with fuel economy and cylinder cooling if correctly configured. By default, most basemaps have it disabled.


You can access the Overrun Settings from the Entity Tree under "Injection", as well as show the status from the "Overrun Status" DRO.



The following settings are present:

Enabled

This allows you to overall enable or disable the Overrun Fuel Cut Strategy.

Min RPM

The minimum RPM for Overrun OFC to operate. If the RPM is below this, then OFC will not activate.

Max MAP

The Maximum Manifold Pressure for OFC to operate. Usually this is the MAP you see when in overrun, and is typically quite a low number, <40KPa in most applications.

Max TPS

This is the maximum throttle percentage for OFC to operate. i.e it will never operate in the above example of the throttle is more than 2% open - obviously because OFC should only operate when the throttle is completely closed.

Min CLT

The minimum temperature that the engines coolant should be before allowing OFC operation. Cutting Fuel during warm up can cause a very "messy" engine to work with.

Init Delay(s) & Cut Time(s)

Once all of the above conditions have been met, a timer will start to count (it is reset to 0 every time the engine leaves the above conditions.) When the timer reaches the time entered here in seconds, then OFC will begin to operate, steadily tapering the fuel percentage over the "Cut Time". If for example the Injectors are at 10% duty normally under these conditions, then once OFC activates in the above example, after 2 seconds, the fuel will taper from 10% duty to 0% duty over the Cut Time, which is 5 seconds. The Injectors will continually now not inject fuel for as long as the engine remains in the conditions.

Return Time

When you return from OFC, for example the driver presses the throttle or the MAP increases due to load increasing, then the fuel percetage will 'softly' regain from 0% back to the normally commanded amount over the time in seconds specified here.


Fuel add trim(%) & Fuel add dur(s)

Because the inlet manifold will have been "dried" during OFC, some extra fuel is usually needed for the return to normal operation. These two settings define by how much the cvommanded fuel amount should be enriched, and also for how long this enrichment should occur