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SONIC, TECH NOTE SERIES
o2 SENSOR MIXTURE METERS & THE TCCS CLOSED/OPEN LOOP MODES
File Name- TNSTCCS1.TXT
Sept 24/96
___________________
TABLE OF CONTENTS:
SECTION A). SDS O2 MIXTURE METER FUNCTIONS
SECTION B). TCCS CLOSED LOOP MODE
SECTION C). TCCS OPEN LOOP MODE
SECTION D). HOW IT REALLY WORKS
SECTION E). CONCLUSIONS
SECTION F). GAUGES AND INSTRUMENTATION.
___________________
GLOSSARY OF TERMS:
EGT-Exhaust gas temperature
O2- Oxygen sensor
TCCS- Toyota Computer Control System {engine computer}
ECU- Same as above TCCS
LED- Light emitting Diode
CLOSED LOOP MODE- Programmed mode in the TCCS
OPEN LOOP MODE- Programmed mode in the TCCS
WOT- Wide open throttle position
SDS O2 meter- circuit card with LED display
SECTION A). SDS O2 MIXTURE METER FUNCTIONS:
The LED display O2 meter reads the very narrow voltage fluctuation that
the O2
sensor outputs to the TCCS ECU. The meter will display a pulse of LED
lights
that are different colors, from left to right the LEDs are colored Red,
yellow and
Green.
*The red LED lights show leaner mixtures than Stoichiometric pronounced
{stock i metric} ratio of 14.7:1 of approximately 14.9:1 to 16.9:1
*The yellow LED lights on the meter suggest the near-perfect Stoichiometric
mixture of 14.7:1. The O2 meter displays the Stoichiometric range on is
two
yellow LED's, they show an air fuel mixture of +/_ 14.7:1, this is the
perfect
mixture required by the Catalytic converters to meet emission tests. NOTE,
this
is not the perfect mixture for producing HP.
Conventional oxygen sensors are designed to be sensitive only in a narrow
range
right around Stoichiometry which is 14.7 parts air to 1 part gasoline.
This ratio
is where the amount of air and fuel is matched to obtain the most efficient
combustion. The Stoichiometric ratio is important to maintain for modern
catalytic converters to operate effectively because this is where the
three
major pollutants are at their lowest average level. At ratios leaner than
14.7 to
1, NOx levels rise while at ratios richer than 14.7, CO and hydrocarbons
rise.
*The green LED lights display mixtures richer than Stoic up to say 11.9:1,
this
is approximately where maximum HP is produced. The perfect mixture for
HP
will vary depending on the engine and conditions. When the first or second
green
LED is on this is very close to the best mixture for maximum HP and Tq.
16.9:1 14.7:1 11.6:1
R R R y y G G
Lean Stoic Rich
SECTION B). TCCS CLOSED LOOP MODE:
When the 7M or 2JZ are in closed loop mode and everything is operating
correctly the LED's will pulse from the far left RED to the first or second
YELLOW LED. Under some conditions the first GREEN LED will light. This
pulse
will increase in frequency depending on engines RPM. Closed loop mode
is used
by the TCCS during, idle, medium to moderate loads. With the throttle
valve open
half way the engines will build boost and go like mad with the half-open
throttle valve, the turbo just blows by the half-open valve. In this condition
the
ECU will not shift to open loop mode and normal fuel mixtures in this
condition
will be approximately 14.5:1 to 15.9:1. As I have mentioned in earlier
tech notes
the EGT temperature is hotter in this condition than under full WOT conditions
where open loop mode is activated by the TCCS. The EGT in this condition
will
hit as much as 1500 degrees' F.
The ECU will use closed loop mode until the throttle plate is opened
about 3/4
open to WOT {put the pedal to the metal}. Revving the engine 6500 rpm
in any
gear with the throttle half open will not cause the ECU to go into open
loop
mode, but the pulsations of the O2 meter will be extremely fast. Open
loop will
not be started until the engine is under high load and the throttle plate
is at or
over 68% throttle opening, only then will the ECU shift to open loop mode.
When
the throttle is wide open the ECU will move to open loop under all conditions.
The mixture will jump to rich mixtures of 11.9 or 12:1 from the very lean
15.9:1. The EGT will start to drop down to approximately 1300 degrees
F.
SECTION C). TCCS OPEN LOOP MODE:
Open loop MODE is only used in the following conditions:
When the engine is cold and warming up at idle the TCCS will use open
loop
mode. As soon as the O2 sensor warms up to about 400 degrees F and starts
to
send accurate output the ECU will shift to closed loop mode. This function
is
necessary to keep the cats from flooding with fuel causing overheated
cats and
exhaust fire. This could happen if the TCCS used the closed loop mode
before the
O2 sensor had come to correct operating temperatures. After the O2 sensor
has
become lively the ECU will only use the open loop mode for high load conditions,
heavy loads for long periods and WOT.
SECTION D). HOW IT REALLY WORKS:
The 1987 to 1995 TCCS ECUs use learned value mode to trim the long and
short
fuel trims, which is shown by the Vf output voltage. The TCCS watches
and
learns what is happening in closed loop mode and this data is recorded
and used
to form the open loop mode fuel calculations. I have learned this information
from very reliable inside documentation on the function and control of
the TCCS
ECU. Some {quote unquote} ECU tuners say that the open loop mode is nothing
more than a fixed map picture in the memory of the TCCS ECU.
I know this is an incorrect statement. I have written proof that the
TCCS learns
where to put the open loop map. It is true that there is a base map that
is in
memory but the TCCS can trim this based on engine conditions, air leaks,
fuel
pressure problems, old age or any of the other possible contributors.
In open
loop mode, the O2 sensor meter will display the shift from the usual pulsating
closed loop swinging LED's to just locking in on one LED suggesting the
mixture
coming down the exhaust system.
SECTION E). CONCLUSIONS:
The TCCS ECU truly is a look and learn system, a fantastically advanced
fuel
system designed for a very refined and advanced high performance street
car
like the Supra. After market ECU's and stand alone fuel systems are good
only
because the ECU programmer is the tuner and has full control of the engines
requirements. This is fine if he knows what the engine requirements are,
I don't
think he does, not without a lab full of equipment. These stand alone
systems do
not have the built in flexibility of the TCCS system. A race car fuel
system is
not what I want in my street sleeper. A street car has many different
requirements than a race car. When I was working the development of the
Lexus
air meter fuel upgrade I witnessed first hand what this little baby can
do. It
learns.
The O2 sensor meter is another useful gauge that gives the driver a visual
look
at what the ECU is doing to keep your engine safe under all the driving
conditions your engine will see. Stop and start traffic, highway cruising
or with
your right foot to the floor board on the street dyno or track. I use
this gauge
along with many other meters to give me a good indication of how the engine
is
doing.
On a bone stock Supra this O2 meter is extra gear most likely not needed.
Your
TCCS is looking at the condition of your engine hundreds of times a second
and
responding to the engine's needs. On the other hand; if the Supra is modified
with the boost cranked up, large injector size, big exhaust, air filters
and
upgraded turbos it is a good idea to see that your TCCS is doing its job
correctly.
SECTION F). GAUGES AND INSTRUMENTATION:
I find the O2 meter good piece of mind, I like to know what is happening
under
the hood. By watching my test probes in the engine bay I know how hard
or easy
my 7M-GTE engine is finding life in my Supra GTE. Some additional readings
I
monitor in my car are as follows.
*Vf output- Jeff M's little fire cracker
*O2 data- SDS meter
*EGT Exhaust temp meter- HKS 60mm peak hold warning meter
*CHT, Charge air temp {before & after Intercooler}- Auto Avionics
*CHT, Cylinder head temp {#six spark plugs base temp}- Auto Avionics
*Oil Temp, {probe in oil pan}- HKS DIN warning meter
*Water Temp {probe in rad side of thermostat housing}- HKS DIN warning
meter
*Oil Pressure- HKS DIN mechanical meter
*Boost Pressure- Auto meter mechanical
Written By
Reg Riemer
/
{SONIC} Supra Owners Network In Canada
FROM THE HOME OF THE SUPRA GTE
Information provided is given free of charge in good faith without prejudice.
Calgary Alberta Canada. T2V-3G6 Hm#403-259-3106
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