[T3] Lean Cruise

[Max Welton]

--- On Fri, 3/8/13, Jim Adney <jadney at vwtype3.org> wrote:
> > The problem I had was that in my normal day, I traverse
> a 1500'
> > altitude change. The fuel law didn't know that the
> ambient pressure
> > was changing and for a while it made nailing down the
> VE-table a real moving target.
> > 
> > Adding the second MAP sensor is one of the standard
> megasquirt modifications. It allows the ECU to read ambient
> pressure 
> > continuously. Problem solved.
> 
> The MAP sensor tells MS what the air pressure is in the IAD.
> That and 
> the RPM are only things that control how much air gets into
> the 
> cylinders. Ambient pressure may have some slight effect on
> the vacuum 
> advance and the air drag on the car, but it doesn't have any
> effect 
> on what's happening in the cylinders. That's one of the big
> 
> advantages of the D-jet system: It's independent of
> altitude.
> 
> I don't see that there was a problem to be solved.

A big part of the tuning process is using an application on a PC called TunerStudio to make real-time adjustments to the VE-table in the ECU to drive the measured AFR towards the target AFRs (also in the ECU). The tool is called VE-Analysis Live, or VEAL.

I work at 6000' and live at 7500' and was running VEAL in both directions. I found that VEAL was leaning-out the VE table in one direction only to enrich those same cells in the other. That stopped after I added the second sensor.

As far as how this plays into the fuel equation, I'm going to refer to the Megasquirt documentation.

http://www.megamanual.com/v22manual/mfuel.htm#equation

Max Welton
http://www.maxwelton2k.net/