Even with a DiabloSport tune, you may find that you are still running a little lean, or you want to try and richen the fuel mixture.
CAUTION: IF YOU DO NOT HAVE THE AIR FUEL RATIO OR ARE NOT TECHNICALLY COMPETENT, DO NOT ATTEMPT THIS PROCEDURE. IT IS BEST LEFT TO AN AUTHORIZED DIABLOSPORT CMR TUNER.
You need to know your current A/F ratio. Without this data, you will not know how far to adjust your fuel delivery parameter. The best way to get your A/F ratio is to install an A/F meter. There are a few threads here on what to use and how to install it.
Ignore the A/F ratio except at WOT. At cruise, the car tries to maintain 14.7:1 automatically. One way to know your A/F sensor is calibrated correctly is to verify it seems to hunt around 14.7:1 at idle.
In some off-throttle conditions, you'll see a huge lean spike - may even just a flash on the gauge. That's because the injectors are shut off to give you engine braking. The A/F ratio in those conditions is irrelevant because the engine isn't under load.
Now, for WOT - tune to 12.8:1 A/F ratio which is where most dynamometers have been showing the best power.
Any significant measurement above the 12.8:1 parameter @ WOT may be too lean. Conversely, any significant measurement below that may be too rich.
You can add fuel using the Predator. Itís important to write down the default parameter for future reference. Also, remember when you adjust it that it's somewhat counter-intuitive. WARNING: If you add 10% and you feel like that wasn't enough and you want it at 12%, do NOT go and set it to 12% on the next one. It's cumulative and that would set it to 22%. You can either reset the parameter to the default data (remember, you wrote this down, didnít you?) or, you can add a small incremental addition. Say you set it at 10%. You tested and you are still lean. You want to be closer to 12.8:1 ratio so you decide to add 2%. Simply add 2%.
Adding or Subtracting Fuel in the Predator:
Go to your XXCAI tune > Modify Parameters > WOT Fuel
You have three tables to work with based on RPM values:
1,000 to 3,800
4,000 to 5,000
5,000 to 7,000
Add or remove fuel in your desired increments to each and every table using the arrow keys on the Predator keypad.
Adjusting fuel amounts is counter intuitive.
Moving the cursor LEFT adds fuel, moving the cursor RIGHT removes fuel.
Differing values for each table are NOT recommended per Diablo Sport. This means that if you add 10% to one table you must add 10% to all tables.
Hereís an example for calculating a fuel adjustment:
Actual AFR divided by Desired AFR.
So for example, if your AFR is coming in at 14.0:1 (a Lean Condition which requires adding fuel), then you take 14.0/12.8 = 1.09, so you would add 9% more fuel.
On the other hand, if your Actual AFR was 11.0:1 (a Rich Condition and you need to remove fuel) and you desired 12.8:1, then 11.0/12.8 = 0.86, so you would subtract 14% fuel.
Once you have changed the parameters, save the tune then reload it.
Remember, setting this parameter more than once results in a cumulative total change.
If you set it at 10% and find you need 12%, do not add 12% when you modify the parameter a second time. Rather, add 2% more for the new total of 12%, unless you decide to return the default parameter and start over. Adding or removing in small increments may be easier for you to do and will help fine tune your fuel settings.
Just remember, these changes won't take until you save your modified tune and reload it.