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 \