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Old 07-22-2014, 06:37 PM   #45
Mack Reeves
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Default Re: EFI, Alpha-N vs Speed Density fueling Strategies

Originally Posted by pbp1 View Post
No, as long as you are not in Closed Loop while on the two step. That is a big no-no!
But whether you are in Alpha-N or Speed Density, the cylls that are not being dropped still need the fuel based on the load and RPM.
When you are on the 2 step, the engine load is still controlled by the throttle and measured by manifold vacuum. In other words, as long as you are on the floor, the engine is still under 100% or max load, the RPMs are just being limited by dropping cylls.
Now, the problem with being in closed loop while on a rev limiter (or two step) is that the dropping of cylls will cause the O2 sensor to read false lean and if you are in closed loop, this will cause a ton of un-needed fuel to be added as O2 correction.
The FAST XFI has internal rev limiters that you can use even if you are using an external ignition box. The benefit of using this feature is that closed loop is automatically turned off when any rev limiter is active, but this only works if you are using the XFI's two step feature. If you are using a different system that does not have this feature, or if you are using the rev limiter in your ignition box, you must set your closed loop activation RPM high enough to be above your two step RPM. Using the XFI's limiter is really nice because you can have closed loop active down low in the cruising around the pits areas and burnout areas. This helps the car run and drive better if you haven't had an opportunity to perfectly tune or "clean up" those driveability areas.
In your above reply you mention that FAST will turn off closed loop automatically when you are on the two step.. Is this in 2.0?? Where do you turn this on or is it totally automatic??? I have been told set your closed loop higher than your two-step RPM... But you do not get the clean driveability I the pit area and other low RPM areas... Thanks in advance for your help.....
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