Throttle cut

From S4wiki
Jump to: navigation, search


Throttle cut is any condition which causes the ECU to reduce the throttle plate angle, even if the actual accelerator pedal potentiometer is at WOT.

The two main causes of throttle cut are

ESP activity (a.k.a. traction control)
The ECU senses that one or more wheels are losing traction. It does this if ESP is enabled and the ABS wheel sensors show a large discrepancy in wheel speeds.
Negative boost deviation
Actual boost pressure exceeds desired boost pressure by around 200-230mbar (3-3.3 psi) for an extended period of time. The ECU will only restore throttle angle once actual boost pressure falls to at or below the desired boost pressure.


Throttlecut.csv shows a 3rd gear run where the ECU cuts throttle.

Notice the throttle plate angle drops suddenly from 100% to 43%-48% when the deviation goes over ~200mbar.

Throttle cut onset
TIME RPM Throttle Plate Angle Boost Pressure Desired Boost Pressure Actual Deviation
497575 4025.75 99.6078431372549 2327.109375 2490.625
497645 4046.75 100 2315.1953125 2508.90625 193.7 .9228 1.084
497716 4114 100 2302.1484375 2503.0859375 200.9 .9201 1.087
497786 4151.5 99.6078431372549 2271.1328125 2508.2421875 237.1 .9055 1.104
497856 4200.5 45.8823529411765 2263.1640625 2488.203125 225.0 .9100 1.099
497926 4230 43.921568627451 2248.3984375 2457.65625

Notice the throttle does not return to 100 until the boost pressure actual returns to almost exactly the boost pressure desired.

Throttle cut recovery
TIME RPM Throttle PlateAngle Boost Pressure Desired Boost Pressure Actual Deviation
499748 5183 48.2352941176471 2200.546875 2222.8515625
499819 5211 48.2352941176471 2208.0078125 2226.5625 18.6
499889 5246.5 48.2352941176471 2216.2109375 2217.34375 1.1
499959 5294.5 77.6470588235294 2220.234375 2194.8046875 -25.4
500029 5319 100 2227.1875 2166.2109375

Getting rid of throttle cut

  • Find and fix all possible electrical or mechanical causes of overboost - N75 failure, leaking or broken wastegate lines, broken wastegate actuators, etc.
  • Adjust the ME7.1 requested load maps to prevent initial boost spikes, or numb the boost deviation thresholds. Alternately, the maps can be adjusted such that the requested boost is always at or above 200mbar below the hard MAP limit. In the latter case, it is strongly recommended that an MBC in parallel be used to prevent overboosting, since the ECU can not know how far above MAP limit the manifold pressure is.
  • Use Lemmiwinks to cut SEL Scaling. However, this also reduces maximum horsepower, so it is not the optimal solution. Also, in some cases it can exacerbate throttle cut, since the requested boost is now lower. If the actual boost remains just as high, there is a higher chance of deviation induced throttle cut.
  • Add back pressure to slow the ramp. If you are using open dumps or test pipes, try using a more restrictive exhaust system.
  • Use the "3/4" throttle mod (putting a stopper below the accelerator pedal), which prevents the driver from pushing the throttle to 100%. This, however, can also reduce overall power.