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During certain situations, the injectors can be turned off. At high RPM, the injectors and spark can be cut off at the Rev Limit RPM in order to prevent the engine from overspeeding and causing engine damage. This can be a fairly sudden jerking feeling, and shouldn’t be used to hold an RPM point. DFCO stands for Deceleration Fuel Cut Off. When decelerating in gear, the MAP is very low, which means the fuel pulsewidths are very small. The engine also has a very high amount of internal EGR, which causes combustion to be very difficult. Also, torque is not even desired, so, fuel can be cut off. This will appear as a very lean condition, but don’t worry – it’s far from any kind of danger – there’s no fuel at all! When the throttle is opened, or the RPMs approach idle, or some other thing causes more load on the engine, the fuel injection returns. Because the manifold will be dried out during the time of no injection, extra fuel “Dfco Return Fuel” is needed to re-wet it, to avoid a long lean out period. Because there are distribution rings in the path of the injection spray, the voids in that ring need to be re-filled as well before fuel will flow steadily out of the discharge holes – Dry Ring Fill PW is used in this situation.

Rev Limit RPM = Above this engine speed, the fuel and spark will be turned off.
Dfco Enable Temp = Above this temperature, Deceleration Fuel Cutoff can be used.
Dfco Cut Fuel MAP = Below this MAP, Deceleration Fuel Cutoff can be used.
Dfco Return MAP = Above this MAP, Deceleration Fuel Cutoff will be exited, and fuel injection returned.
Dfco Return Fuel = When the fuel injection returns, extra fuel is required to wet the intake manifold walls, to avoid going lean
Dry Ring Fill PW = The fuel distribution rings need to be re-filled – since they don’t change size, this value should be correct in the default calibration.
Max drpm Drop rate = If the RPM is dropping very quickly, such as when shifting gears or other clutched event in a manual transmission, Deceleration Fuel Cutoff will be exited early, and fuel injection will return.
Fault Rev Limit = In the case of some sensor faults, the rev limit can be reduced to act as a protection and as a warning in case the driver wasn’t aware of a fault.

8 comments on “REV LIMIT DECEL CUT

  1. Can I change the settings of this on my hand controller?

    1. Yes. This is an adjustment menu in Go EFI Tuning.

  2. I’m getting my new system set up, it seems to ‘hang’ at about 1200-1400 rpm when coming back down to idle for a moment, then settles back to the set idle rpm. Is there a way to adjust for this? its a SBF with a manual trans.


    1. This is normal for EFI. We do it on purpose and should catch the RPM about 300 rpm above the target idle speed.

  3. Exhaust pops when I decelerate. How do I adjust?

    1. This is normal because fuel is being shut off under decel. If you should off decel the popping will go away. Just change Decel Cut MAP to 5.

  4. Engine almost dies after decelerating with a manual transmission.

    1. Change your cut map down to 18 and the return map to 20. Test this out and if you are still having issues try taking them to 5. This will shut off decel fuel cut.