sorting out my proflo, one issue

[Mike R Brown]

Jason Haines wrote:
> 
> Do you have a way to check air fuel ratio (other than the rich/lean
> indicator in the Pro Flo)? When you get the Pro Flo O2 sensor installed,
> check to see if you are going leaner than 14.7 (red light)? How about fuel
> pressure - any chance you are loosing fuel pressure under those conditions?
> I am working with a Pro Flo right now and I am chasing a transient fuel
> condition (goes lean) that will not respond to global or transient fuel
> changes (I too have gone as high as 20% without any change in the
> condition). It looks like the fuel pressure is dropping when the lean
> condition occurs. The other less likely issue could also be fuel rail
> "hammer" - does the fuel pressure start jumping up and down very quickly
> when the problem occurs?
> 
> Jason
> 

	There is not much transient management in the stock Weber code at all. 
A little extra added as the TPS changes, a little more when it detects
an increase in load (via remembering what the MAP ADC reading for the
last injector firing on the current cylinder pair).  Transient Fuel
modifier doesn't do what you might expect and when you'd expect it to. 
It modifies the decay rate of extra fuel added, but this transient fuel
is for higher RPMs and delta loads.  The built in A/F tables are very
lean in the off idle region.  Increasing Global might help if in your
situation the lean condition wasn't too bad, but what tends to happen
that the regions bounding this are gets way too rich and the engine
continues to stumble masking the condition you are trying to fix.
	These units have a problem with how they deal with the air temperature.
With the MAT sensor mounted in the rear of the manifold all you are
reading is the temperature of the aluminum.  You might notice when you
get the motor good and heat soaked, that when you move the throttle off
of the idle stop the MAT reading on the display changes.  This isn't
because fresh air is moving past the sensor as you might think.  They
artificially limit the MAT reading at closed TPS to fake the code so it
thinks the air is denser than it really is thus making a richer
mixture.  This is the Band-Aid trying to fix the 'blower roll' problem. 
It doesn't...
	Another problem is the code that detects the wide shutter in the
distributor to synchronize the injectors doesn't work.  Every time you
start the motor the injectors are spraying on a different pair of
cylinders.  If it would stay the same at least you could tune it for
that condition, but changing every time you start it you can drive a
person nuts.  This also can lead to some weird stumbles.  As the RPM
increases the phasing of when an injector pair fires changes.  This is
to let the fuel vapor sit on top of a closed valve for a bit of time. 
One of these phase changes occur just above 1500 rpm, right in the
middle of the stumble zone.  With the injectors out of sync sometimes
you are spraying on a closed value, sometimes on an opened valve, and
sometimes on a closing value.  An engine with an aggressive cam in it
magnifies these problems.

Good Luck,
Mike
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