[alfa] Bigger injector comments...

[Eric Storhok <alfa@xxxxxxxxx>]

I won't spend much time echoing the very correct comments that bigger 
injectors really don't buy much, and that re-mapping will give you the 
proper fuel mixture easier.

Some other comments, thought-
The O2 sensor is the fastest of all the gas sensing sensors on the car- if 
you have one cyl that is just barely lean, while the others are barely 
rich, its quite capable of seeing it.  We have to design around this, 
actually, as it can cause some interesting a/f control problems....  What 
is slow is the computer's reaction to it.  Well, not exactly slow, but more 
correctly, measured.  The reaction rate is a rather large input to the 
ability to meet emissions, as you want to properly balance the time rich 
and the time lean to optimize emission.  Even for a large excursion rich or 
lean, it will ramp the same way, and it takes a while to get there.

Also, to assume that the O2 sensor will adapt to any changes is not quite 
correct.  Most computers have a limit to how rich or lean they will go to 
try to correct.  I'm fairly sure that the early Bosch cars will go pretty 
rich when it sees a lean signal, probably as rich as 9:1 at the extreme- 
this based on the data I get from all of you who try to drive with dead 
sensors plugged in.... ;)  Anyway, typical digital systems only correct 25% 
before giving up.  True, that will cover the majority of changes...  but 
that also assumes that the adaption software corrects in the areas that are 
open loop...  (the only faster sensor on the car?  crank position)

Finally, whoever mentioned that their engine ran too lean with the original 
mapping (I think that was you, Peter), you might want to check out why.  I 
would more expect that the engine would run overly rich and not lean- which 
means that "ideally" leaner to about 12.5:1 would peak the power.  The 
reason I think this is that all OEM's know that we are allowed to do 
virtually anything to save the catalyst, and a rich mixture when open loop 
keeps the exhaust temps in order.  Earlier systems are far more crude than 
current modern ones that delay going open loop until a temp model says so, 
which is another reason I would expect all the Bosch cars to run 11-11.5:1 
at WOT.  If it's not, you might want to look into why, specifically leaks...

Eric Storhok
Ann Arbor, MI

AROC Detroit Homepage:  http://www-personal.umich.edu/~alfa/index.htm
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