Throttle cut
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Contents |
[edit] Definition
Throttle cut is any condition which causes the ECU to reduce the throttle pedal 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.
- Boost deviation
- Actual boost pressure exceeds desired boost pressure by around 200-230mbar (3-3.3 psi). The ECU will only restore throttle angle once actual boost pressure falls to at or below the desired boost pressure.
[edit] Examples
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.
| 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.
| 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 |
[edit] Getting rid of throttle cut
- 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.
- Use a master boost controller in parallel to set a hard limit on the actual boost.
- Use a throttle cut defender to "trick" the ECU into thinking the actual boost is lower than it is.
- Adjust the Motronic ME7.1 boost maps to prevent initial boost spikes. 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.
