[T3] Lean Cruise

Max Welton max_welton_2k at yahoo.com
Fri Mar 8 21:24:48 PST 2013


The engineer in me needs to explain this. Then I promise to 
leave it be. ;-)

--- On Fri, 3/8/13, Keith Park <topnotch at nycap.rr.com> wrote:

> Well, the D jet can apply a super
> lean condition to light throttle if you
> get the inner stop on the pressure sensor adjusted wrong,
> and I guess this
> has lunched engines in the past.  Im not sure exactly
> how this would compare
> with your profile, but its something to be careful about...
> you don't want
> to hear any knocking and pinging and on a square anyway, its
> REAL easy to
> hear that if its occurring with the engine lid off.

Sure. Makes the cabin smell bad though. ;-)

> Just keep an eye on the oil temp and more importantly the
> head temps.  You
> may be able to get away with things at altitude that we cant
> at sea level.

See, that's the thing. At sea level, as you pointed out, 
aero drag goes up. As I counter with more power, MAP goes up.
If it exceeds 65 kPa, my AFR goes back to the low 13s. 
I might not see the mpg I get at altitude, but the engine 
will be safe.

Now, that 65 kPa will occur at a smaller throttle position 
at sea level because ambient pressure is greater. The
reason throttle position is important here is that it 
effects the vacuum advance signal. The amount of ignition
advance appears to have an effect on measured AFR independent 
of the amount of fuel being supplied.

BTW, that 65 kPa threshold I'm using was arrived at 
experimentally by sifting through hundreds of hours 
of driving data logged through the ECU on a laptop 
riding in the passenger seat. It turns out that 
the coolant sensor mounted in the head reacts fast 
enough to allow me to tell when I'm moving things 
in the wrong direction.

> One thing I CAN say, some of the D jet "experts" get it
> wrong sometimes and
> Have gaps in their knowledge as well.
> 
> Keith

They aren't the only ones (cough). 

OK, I'm done.

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




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