Re: CIS-E fuel modification @ WOT

["Scott Mo." <scottmo@teleport.com>]

CIS-E Gang,

I have read a few of the posts regarding the add on WOT coolant temp
sensor resistance change and modifying the PA current etc. but I haven't
followed this thread too closely, so forgive me if I am missing out on
something. I don't want to rain on anyones parade, but here are a few
thoughts regarding this sort of modification:

On the CIS E and CIS E-III equipped vehicles, has anyone measured the
exhaust gas composition under WOT conditions to see what the actual A/F
ratio is? There seems to be some assumption that the A/F ratio is too
lean at WOT and faking out the coolant temperature sensor or adding more
current into the Differential Pressure Regulator (PA) will make the A/F
ratio richer and thus "better". 

I think it is important to know where you are starting from, A/F ratio
wise, before anyone goes out and feels they need to richen up the
mixture. It is quite possible that the A/F ratio is already rich enough
(close to 12:6 to 1) as is provided by the design of the air funnel in
the CIS air flow meter and by the fuel injection system with the extra
current sent to the Differential Pressure Regulator (PA, Pressure
actuator current)

Now regarding the exhaust gas measurement, I am not talking about using
one of the inexpensive O2 sensor A/F ratio meters, despite everyones
claims, they don't accurately measure A/F ratios below 14:1. I am
referring to a 4 or 5 gas portible exhaust analyzer ($5000) that can be
used during an actual road test. I suppose a FWD coupe could be tested
on a dyno under load with a stationary exhaust analyzer that most Auto
repair shops have.

A couple of other things to keep in mind:
The CIS-E-III uses a ignition control unit and a fuel injection control
unit, the coolant temp sensor has two temperature sensors inside (both
use the same resistance curve) and these two resistance readings are
sent to each control unit.  The ignition control unit has two timing
maps programmed inside, one for regular fuel and one for premium fuel. 

The premium timing map will provide greater torque at a lower engine
speed. The ignition control unit will switch to the premium fuel timing
map whenever the coolant temp is above 149F (65C). The knock sensor will
retard the timing several degrees at a time, if it senses knock and if
necessary after sustained knocking, the ignition control unit will
switch to the regular timing map. So if you fake out the coolant temp
sensor resistance on this vehicle, the ECU may use the regular fuel
timing map which isn't what you want for performance.

The service training booklet for this CIS-E-III indicates the following: 
"During full load operation, the fuel mixture will be enriched to
provide maximum engine output. When the full throttle switch is closed,
the fuel injection control unit will increase the differential pressure
regulator current by about 3mA. This value will vary slightly according
to engine speed. When operating in high altitude areas, this value will
also be lower. 

Altitude Correction:
The fuel mixture will be corrected according to altitude and air
presure. This is based onthe signal from the altitude snesor.
As altitude increases and air presssure decreases, the current to the
differential pressure regulator will be reduced to slightly lean the
fuel mixture. Tis isonly effective during open loo coinditons cuas as
warm-up and full throttle enrichment. It has no effect during oxygen
sensor regulation (closed loop). 

Deceleration and Engine Speed limitation

During Engine Deceleration, fuel to the injectors is shut off byh
increasing the negative current to the differential pressure regulator
to about -50 to -60mA. This helps reduce fuel consumption and exhaust
emissions. The engine speed at which this will occur is regulated by
coolant temperature.

This will also ocur at about 6600 RPM to limit the engine speed" 
End quote:

The CIS-E-III uses a differential pressure regulator current between
+10mA (rich) to -10mA (lean). The nominal CO% adjustment point is 0mA.

The earlier CIS-E uses a differential pressure regulator (Pressure
actuator) current between  +120ma to -40ma, this corresponds to a
differential pressure of ~1.6 bar to 0 bar. This is the pressure
differential between the upper and lower chambers that regulate the
amount of fuel that is sent out to the injector.

The service info on the earlier CIS-E system indicates: 

"CIS E vehicles are equipped with a full throttle enrichment. Full
throttle enrichment will only take place "after" the engine has reached
operating temperature and provides additional fuel for the increased
performance requirements of the engine. When the engine speed is above
4000 RPM, and the throttle is fully open, the full throttle switch,
located on the throttle housing, closes sending a voltage signal to the
electronic control unit. The control unit increases the differential
pressure regulator current to a fixed rate that is approximately 3 mA
above the basic adjustment value to enrich the fuel mixture." 

CIS-E Acceleration enrichment:
"Acceleration enrichment will also only take place when the engine is
below normal operating temperature and is only effective for a few
seconds. The amount of acceleration enrichment is dependent upon:
Engine coolant temperature, Movementspeed of the air flow sensor plate
potentiometer, total travel of the air flow sensor plate, and engine
RPM. The resistance curve of the sensor plate potentiometer is such that
the rate of enrichment si great at lower engine speed and less at higher
engine speed." End quote.

I have the coolant temperature resistance chart versus the coolant temp
for the CIS-E, CIS-E-III. 

If you consider the sophistication of these systems, doing some sort of
hack that fakes out the coolant temp sensor may not get you where you
want to go, performance wise. Doing a minor increase on the PA current
may work, provided you can actually measure the corresponding change in
A/F ratio and you know what the A/F ratio is for a stock setup before
the modifications. 

Your mileage may vary, especially if you fool with the CIS injection
system.....
-- 
Scott Mo.
1989 200TQ
http://www.teleport.com/~scottmo