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Re: The "Power Box"

> It seems to me that the "Power Box" advertised in the Roundel (modifies the
> fuel injection pressure) might not work on some BMW's.  Most of the fule
> injection systems in late model BMW's have a fuel pressure regulator that
> keeps pressure constant and dumps excess fuel back into the fuel tank when
> pressure increases.  The amount of fuel sprayed into the cylinder is a
> function of how long the injector stays open.  The fuel pressure does not
> change.  Maybe the power box somehow disables the pressure regulator or
> requires its removal.  Has anyone installed one of these yet?         

The amount of fuel sprayed into the cylander is a function of both 
injector duty cycle as well as fuel pressure.  Fuel injector 
manufacturers often publish an injector's flow, but this is in terms of a 
certain pressure.  All high pressure fuel systems work by dumping exess 
fuel to the tank.

Does anyone out there know just how much extra pressure motronics will 
handle before the closed loop compensation will not longer compensate?  
This will more than likely result in: Poor emissions, Poor gas milage, 
increased engine wear, if you go too far it may even melt down your 
catalytic converter.  Ooooh, sign me up for one of these!  It seems like 
this device is nothing but an aftermarket pressure regulator!.  These are 
cerainly not _that_ expensive!!!

This device could be usefull if you did some extensive engine work (hot 
cam, bigger displacement, etc...) and needed more fuel pressure.  Most 
engine systems do not run in closed loop mode at full throttle, so your 
engine setup may _requre_ fooling the computer into supplying more fuel 
(easiest way = bumping fuel pressure), so the engine was not running 
too lean at full throttle.  At part throttle it would hopefully read the 
O2 Sensor and reduce injector duty cycle accordinly, provided you were 
within the computer's margin for error.  Some computers would probably 
have limits on this duty cycle.  (the computer may eventually think HEY! 
at this rpm, load, air flow reading, the O2 Must be wrong! and maybe give 
an error flag.)

I have been studying fuel injection systems in detail in the last few 
months, and have made a few assumtions in the above paragraph.  If anyone 
can correct my logic above, please do so if it is at fault.  I am 
currently assisting a friend in developing our own fuel injection 
system.  Our prototype so far is running in "alpha-N" mode (judjing duty 
cycle buy reading only throttle angle and RPM... tune with a laptop)  
The  prototype is in a friend's drag race Mustang and is both the '94 
points leader in his class and the record holder (AMRA S/S).

Larry Harris
'86 Mustang LX 5.0 Coupe   '82 BMW 635CSi Euro
Meyers Tow'd Dune Buggy    '83 Toyota Tercel (178K)
People who live in stone houses shouldn't throw glasses.