[T3] Lean Cruise

[Max Welton]

--- On Fri, 3/8/13, Jim Adney <jadney at vwtype3.org> wrote:
> Second barometer? Is that a second MAP sensor?
> 
> Please explain.

At power-up the typical megasquirt ECU takes a single reference 
sample from the MAP sensor to represent the ambient air pressure. 
This happens in the instant before the engine starts turning. 
Ambient pressure is about 80 kPa in COS and something like 100 
kPa at sea-level.

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.

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