Way too rich on boost

[MichaelR32GTR]

I’ve been collecting some logs and my on boost afrs are going super rich on boost

 

on a rb26 - 2.8 stroker with 76mm precision, E85 on about 38psi boost, starts off fine around 0.78/0.77 lambda, then from 7000rpm onwards it starts going 0.75 lambda, then 0.74, 0.73, 0.72 by 8500rpm

 

i have made some adjustments via afr target table but that didn’t change anything 

 

I’m assuming next thing to do is adjust via VE table, question is, how sensitive  is the table, will removing a value of 1 say instead of 101 to 100 be a big enough change to see it slightly leaning out ?

[Adamw]

Im assuming it is still ITB's with TP Vs RPM on the main fuel table?  Typically for this type of set up you would enable a 4D fuel table with MGP Vs RPM on it's axes, most of it will be zeros with some fuel pulled out in the high boost/high RPM corner.  

[MichaelR32GTR]

 

Main Fuel table is TP vs RPM yes, 

In FUEL—> FUEL CORRECTIONS—> 4D fuel table is ON

 

On its axis is MAP (KPA) and RPM

yes your correct, table is mostly zeros except for around 6500rpm and 280, 320, 360kpa which has 1.0 in that row

then 7000rpm to 9000rpm and 280,320,360kpa has 2.0

 

im not familiar with this table sorry, is it basically adding fuel in the rows with 1.0 and 2.0 ?

 

[MichaelR32GTR]

I should add that as I lower boost to say 33/34psi (or so) that it’s target afrs are perfect, as I raise boost from there to high 30’s it starts going super rich 

[rrob]

The 4d table should be removing fuel as the turbine back pressure rises. 

[MichaelR32GTR]

So I should have values in the minus at the desired areas 

[Adamw]

Yes, negative values in the 4D table.  "-5" in the table would remove 5% fuel.  

[MichaelR32GTR]

Thankyou !!

[MichaelR32GTR]

Working out some calculations for how much fuel I should add 

 

just a question in regards to existing values in the 4D table 

 

if in one box it currently has a value of  “2.0” and I need to remove 4% of fuel, would that value now be “-2.0” which is taking away the existing 2.0 value and then another minus 2 to give -4% ?

 
thanks !!

 

 

[Vaughan]

1.02 * 0.96 = 0.9792 so to remove exactly 4% you would use a value of -2.08 (would have to be -2.1 for the 1dp available in the table) but yes -2.0 would be around a 4% reduction from +2.0

[MichaelR32GTR]

Now that I have taken some fuel out using the 4D table and it’s targeting 0.77 lambda nicely 

 

should I change my afr target table to match the 0.77 afrs on boost?

 

afr target table on boost is currently on 0.85 lambda 

 

or won’t matter and won’t make a difference and just leave as is 

[Adamw]

If open loop lambda table is on then you are meant to tune to the target that is in the table, you if you change the target later the AFR will change automatically without retuning.  If you change the target now it will go very rich.

But it would be best to change the target then retune so the measured lambda does match the target.

[MichaelR32GTR]

I haven’t had much time to finalize tweaking afrs, but I’m headed in the right direction with the help I was given 

 

can I ask, if 4D fuel is enabled, what would happen if all the boxes are 0 and boost is increased instead of removing fuel with minus (-) values 

[Electredge]

21 minutes ago, MichaelR32GTR said:

I haven’t had much time to finalize tweaking afrs, but I’m headed in the right direction with the help I was given 

 

can I ask, if 4D fuel is enabled, what would happen if all the boxes are 0 and boost is increased instead of removing fuel with minus (-) values 

If 4d fuel is enabled and the table has only zero's then it will be doing nothing to change the fueling. It will basically be multiplying the final fuel value by 1