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Fuel or Ignition mode for RPM limit.


Jeremy Towers

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I am hoping someone can tell me how the RPM limit works in progressive "Fuel Cut" mode. I recently activated my RPM limit on this setting and noticed a puff of white smoke form my exhaust which I would normally associate with detonation. A leaning of the mixture at full throttle sounds dangerous to me. Does the ECU cut fuel completely to certain cylinders? The explanation in the help menu is rather... limited, so hopefully someone can elaborate. My engine is running with sequential injection by the way.

Thanks

Jeremy

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Hi Jeremy.

It would be wisest to use ignition cut in most situations as the extra fuel on cut cylinders is not going to hurt anything, and infact can provide some cooling (it can create pops and bangs in the exhaust with the unburnt fuel however).  The progressive cut works the same on fuel and ignition, where there is a pattern in the background cutting certain cylinders in one of 2 ways.

The two ways are 'adaptive' and 'constant'.  The adaptive makes sure the same cylinders are not being cut every single time, allowing for even heat distribution (not heating up some cylinders more than others for example).  The second cuts the same cylinders everytime... This exists as a preference for some people only, as it does give a slightly smoother feel.

If you have that down (how it's cutting), it just leaves explaining the progressive thing, which the help file does quite well (below).  In effect, you end up with a cut feature that doesn't plaster you against the windscreen (progressive)... It will use a percentage of the full cut set by you, based on your TPS and Control Range settings in the 'advanced mode'.  And progressivly reintroduce everything at a specified rate... ie. Not ALL THE POWER BACK AT ONCE - Which is handy mid-corner ;)

If you are not using the advanced mode, it still works the same but the values 'limit ignition trim' and 'limit control range' have been preset to -5deg and 200RPM respectively, and cannot be adjusted.

Hard Cut (Advanced Mode Feature)

This setting selects whether a hard cut will be implemented at the point specified by the Hard Limit Addition. The following options are available:

· OFF - hard cutting is turned off.
· Ign 100% cut - the hard cut is ignition only.
· Fuel 100% cut - the hard cut is fuel only.
· Fuel and Ign 100% cut - the hard cut is both fuel and ignition.

 

Percentage Cut

The percentage cut is a measure of the amount of power cut from an engine. For example 0% cut is full power, and 100% cut is the engine turned off.

 

Limit Control Range (Advanced Mode Feature)

Specifies the RPM range that the limiting operates over. The Limit control range operates under the specified RPM limit. For example, with a RPM limit set to 7000 and a control range of 200, the limit would operate between 6800 and 7000 RPM. A typical Limit Control Range would be 200RPM.

 

Limit Ignition Trim (RPM, MAP and Speed ONLY) (Advanced Mode Feature)

Specifies the amount of ignition trim applied when limiting system is active. A typical value would be -5 degrees.

 

 

Hard Limit Addition (Advanced Mode Feature)

Specifies the RPM past the end of the Limit Control Range at where the hard limit will apply. A typical Hard Limit Addition would be 200RPM.

 

Cut Effect (Advanced Mode Feature)

The cut effect specifies the type of cutting sequence.

· Adaptive - the cutting sequence is continually adapting for a particular percentage cut. (Typical Setting)
· Constant - the cutting sequence is fixed for a particular percentage cut.

 

End Cut (Advanced Mode Feature)

Specifies the percentage cut at the end of the control range. A typical End Cut value would be 90%.

 

Start Cut (TP 100%) (Advanced Mode Feature)

Specifies the percentage cut at the start of the control range with 100% throttle. A typical Start Cut (TP 100%) would be 60%.

 

Start Cut (TP Low) (Advanced Mode Feature)

Specifies the percentage cut at the start of the control range with TP Low throttle. A typical Start Cut (TP Low) would be 30%.

 

Note: If Start Cut (TP Low) is set above Start Cut (TP 100%), only Start Cut (TP 100%) will be used.

 

TP Low (Advanced Mode Feature)

Specifies throttle position at where Start Cut (TP Low) applies. A Typical TP Low would be 15%.

 

Note: If TP Low is set to 0, throttle position will not influence the start cut. Only the Start Cut(TP 100%) will be used.

 

Exit Decay Rate (Advanced Mode Feature)

Specifies the rate at which the percentage cut is reduced after exiting the limit. This is measured in % cut reduced per 20ms. A typical Exit Decay Rate would be 1.

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