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Old 11-24-2010, 09:44 AM  
Poolside OP
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Joined: Apr 2003
Location: Long Beach, CA
Oddometer: 11,865

In a nutshell if you don't mind, cause JJ and I are going to get into much detail later. Color illustrations too!

When the motor is running at a steady state RPM, and the throttle isn't being moved at all, the ECU is in closed loop.

If the throttle is advanced any amount from that steady state, any tiny amount to make the RPMs rise, the ECU is in open loop. There's a lot of complexity in this 'transitional state', especially with small throttle advancements.

At some point after the throttle angle was changed, the motor 'meets up with the throttle' say, and again maintains a constant RPM. The ECU returns to closed loop.

There's a lot of mythology about what happens during open loop and closed loop modes. Much of it concerns how rich the mixture is in either mode.

You know when you traveling at 50mph on a hot day, and just b-a-r-e-l-y crack the throttle, the motor often immediately pings a few times, or feels like it goes 'soft'? That's part of open loop operation.

The EFI's version of the carburetor's accelerator pump is the majority part of that transition. And that softness cannot be fixed with air temperature adjustment. It can be helped a little that way. Maybe a 30% improvement.


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