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Fuel table values not necessarily increasing with increased MAP


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Hello all,

Ive noticed when approaching 20psi mark, that whilst the AFR remain good, im not actually requesting higher figures in my fuel table.

IAT are in a good place, normally increases by around 10c after the pull in the current weather, finishing at 30c. ambient is around 10c.

Is this a case of running out of efficiency, or possibly high back pressure? 

There is a rising rate fuel reg, and pressure is increasing accordingly with MAP. Differential fuel pressure at the start of the run is 310kPa to 290kPa

Any help appreciated,


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If on 'Fuel Equation Mode' = 'Modelled', this is quite normal. The values in the fuel table is volumetric efficiency, not actual percentage of master fuel (like in traditional mode).
Post a copy of your tune file and short log showing exactly what you have described above.

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Even in traditional mode the the injector pulse width is already multiplied by MAP and target lambda, so assuming volumetric efficiency is relatively constant then the fuel table number shouldn't change with boost.  The traditional fuel table should give a similar shape as a modelled/VE fuel table.  

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I hugely appreciate that. Thankyou. Where I had scaled up the table for increased Map, I felt concerned I was then reducing those numbers to be on target for my AFR.




On a similiar note. Would the numbers ever decline, would you actually notice running into high back pressure, or is that never reflected in the fuel map?

I had assumed, that the fuel map would generally be a result and a picture of your torque curve at least 


Thankyou again for your help

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Trying to think of a better way to explain it but having difficulty finding the right words.  You can think of the fuel table as an indication of volumetric air flow, or air flow assuming the density was standard atmosphere conditions (ie boost pressure only affects the mass, not the volume).  Anything that restricts the volume of air the cylinder inhales will reduce the fuel table number.  So yes, increasing the restriction or "back pressure" on the exhaust side would reduce the fuel table number just like a partially closed throttle etc on the intake side.  

The fuel map shape will reflect the torque curve assuming the engine was NA, then boost pressure is basically a multiplier on top.  

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