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Rich Spot After Revs


Jeffersonc
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So I'm in the process of street tuning my RB25 and would like some advice on what I could adjust to eliminate this rich spot in my tune. It's only after I rev the engine, (the throttle plates are now closed) It stays good for a quick moment then goes really rich then finally clears up. It also happens when driving and I decelerate. For a split moment it will go rich before the decel fuel cut comes active. I have changed the accel from 60% down to 30% but with no change. It revs up nice and clean without issues. This is an RB25 with RB26 ITBs if that makes a difference. I am street tuning and breaking it in (first time tuning) before going to the dyno and getting my tuner to start adding boost and making any required changes. 

I tried attaching a small video but it was too large. 

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Yup, that was my plan on tomorrows drive, I will log it and get you that.
How does the master fuel work? Reading the help browser it makes it sound like it's the set amount of time (ms) the injector sprays fuel for every injection event. This would require you to make adjustments to fuel table 1 to achieve the same targeted afr numbers lets say.
If I make correct sense of this, then perhaps my situation with having the ITBs is, once they shut it becomes such a sudden "stop" in airflow through the intake ports and engine vs a single TB that would give a smoother off throttle movement due to the greater plenum volume. 
I can work off that trying both directions and seeing its effects , if I'm making sense of this?

Found a solid forum post explaining it. Other then his stalling issue, its a ton of good information I can use. 

https://www.hpacademy.com/forum/general-tuning-discussion/show/link-g4vi-pec-vxx-master-fuel-setting

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No, the fuel master is just an overall multipler, you just use this to initially scale the fuel volume to suit the injector size etc.  You only need to change it if your fuel table numbers are too big or too small, yours are a little small but not enough to be a problem I think.  If you halved your master fuel then you would need to double the numbers in your fuel table to get the same fuel volume injected. 

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On some forum someone mentioned that the fuel equation was about something like this, for what it's worth :

Base pulse width= Master Fuel x MAP/100 x %VE/100

This means for example that if we substract 25% from, or multiply by 3/4, the Master fuel we therefore need to add 33% to, or multiply by 4/3, the values in the Main Fuel table (%VE) to get the same Lambda correction. I did just that and was able to confirm from checking in the Real Time values table that the % of Lambda correction was exactly the same as before. Since 100 is the maximum value that can be entered in the Main Fuel table the maths simply say that reducing the Master Fuel "will allow" or "require", depending which way you look at it, a higher resolution/finesse of tune from the Fuel Table and logically result in a "smoother" Fuel Table without peaks and valleys that some folks occasionally comment about

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Note all this is explained in the help file.  If you have the help browser open and click on any ecu setting, the help browser will give you an explanation or further information about that setting.  Below is what you get if you click on master fuel:

UKY2E3g.png

 

Also, the fuel table can take numbers up to 150.0% and it is not VE, it is just "percent of master".  It will not make your table smoother, but if you have very small numbers in your fuel table then you will lose resolution since the smallest adjustment increment is 0.1%.

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