Re: CIS-E fuel modification @ WOT

[ejfluhr@austin.ibm.com (Fluhr)]

Q-list resident-theorist Tony Lum proposes:

>Please excuse lame ASCII art, but here is my proposed change to CIS-E using
>existing WOT switch, one 12 volt SPDT relay and a resistor TBD (to be
>determined).  The resistor would be picked based on desired enrichment at
>WOT and should have zero effect at cruise.
>
>WARNING: use this circuit at your own risk-its a cerebral/experimental
>excercise for right now.  Bruce Bell is in the process of trying this out
>to see if there are any potential gains.
>
>Comments invited :^)

My main concern is how the ECU reacts to the sudden change in resistance
(i.e. voltage level?) it sees at the temp sensor.  Will it instantaneously
jump into is cold-run enrichment mode, cranking the pressure actuator
current from ~10mA to ~40mA (give or take, depending on the value of 
your FS resistor)?  Perhaps the CIS-E III systems will suspect something
is wrong and flag a fault code?

Also, you might have to be careful with tripping the WOT switch at
low rpms ( < 3000?), since the mixture may be too rich for the car and
cause the engine to bog.

I still like the idea of changing the 3mA value in the ECU to something
higher, perhaps around 10mA.  If this value is stored in a PROM, perhaps
it can be found and changed.  It is certainly a much more elegant
solution than a black-box add-on (whether it is made by Techtonics Tuning
or the "Quattro-List Black-Box Club" ;).


For those with a "Bosch Fuel Injection & Engine Managment" book, there
is an interesting picture on page 28 of the "Continuous Injection - Theory"
section.  It should that, assuming the engine is running at 10mA of
pressure actuator current at 14.7:1 air/fuel, 12.6:1 is somewhere near
20mA.  This is only an increase of ~10mA.  Can you achieve that by
using the fake-temp-sensor method?

Another interesting idea that occured to me is that it is better to
trigger the WOT switch later in the RPM range rather than sooner, which
seems to be supported by my driving experiences.  If you trigger the
WOT switch at ~3000rpm and hold the throttle down, the engine goes
open loop right away and enriches the mixture, giving you a bit of
extra power.  However, as the rpms increase, the ECU (I am guessing)
holds the pressure actuator current static, so that the engine starts
to approach stoichiometric, then surpasses it and begins running lean.

Now, if you run just shy of the WOT switch until, say, 5000 rpms, the
ECU will maintain the air/fuel ratio at stoichiometric.  Then, when
you close the WOT switch at 5000rpms, you get that extra bit of
enrichment, giving you a tad bit extra power, which is better than
the lean condition theorized about in the prior paragraph.


Later,
Eric
'85 Coupe GT
---
Eric J. Fluhr                                Email:  ejfluhr@austin.ibm.com
630FP Logic/Circuit Design                   Phone:  (512) 838-7589
IBM Server Group                             Austin, TX