rap2chin;1689963 said:
I sorry I mean the boost guage is hooked up. So is the boost controller I'm hopin its hooked up correctly. My boost controller is all the way up and I'm still just runnin 8psi. Why? I want 12 dang it. Haha. And real quick. What the point of havin an SC400 afm?
Taken from
http://suprasonic.org/lexusriemer/lexusnotes.html
SONIC TECH NOTE SERIES:
Information provided is given free of charge in good faith without prejudice.
January 21, 1997
THE 7M-GTE TCCS, LEXUS AIR FLOW METER UPGRADE AND Vf DATA v2.3
File name: LEXUSair.txt
Hi Supras. I wrote this TNS in response to many requests for info on the Lexus air flow meter upgrade and its functionality, as well to answer questions and misunderstandings of the TCCS's {Toyota Computer Control System} Vf line output information and the learned value trim system. As the Vf output and the Lexus airflow meter upgrade are related topics I thought I would write this tech note paper to explain the systems in more detail.
INTRODUCTION:
The Lexus V8 engine uses the same type of Karman vortex air flow meter design as the 1987 to 1992 Supra 7M-GTE turbo engines. The only difference in the two air flow meters is the size of the air flow meters two main passage ways, or chambers. The Lexus air meter allows more total air flow through the meter at the same Karman vortex square wave frequency.
When air passes through the Karman vortex air flow meter, a vortex generator creates a swirling of the air downstream of the generator. This swirling effect is referred to as a Karman vortex. The frequency of this Karman vortex varies with the velocity of the air entering the air flow meter and other variables. A photocoupler LED and metal foil mirror are used to detect changes in these vortices. This system generates a variable frequency square wave signal that is sent to the TCCS.
Because the Karman Vortex is not a mass type air flow meter, the Karman Vortex system must use other sensors for density and temperature correction compensation. Example: The air temp sensor is located inside the Karman Vortex air flow meters sensor unit but is a totally separate measuring system for the TCCS.
The HAC sensor {high altitude compensation} sensor is located inside the TCCS on 1989 to 1992 7m-GTE's engine and mounted externally from the TCCS on the 1987 &1988 7M-GTE's. As the frequency of the square wave {Karman Vortex} varies with the intake air density. Due to this fact air and altitude corrections are necessary in the TCCS by using the HAC sensor data.
If the Karman Vortex air flow meter system were to fail completely the TCCS will enter Fail Safe mode. Under this mode injection pulse width and ignition timing will be set to the Fail safe fixed values based on other engine sensor conditions. This is the normal injection pulse width and ten degrees fixed ignition timing.
The variable frequency square wave signal is how the TCCS engine control computer knows what volume of air is entering into the engine. The square wave signal is output by the air meters electronics to the TCCS ECU. This signal is a five volt signal switching on and off faster and faster as the volume of air passing through the air flow meter is increased.
If the TCCS reads an air flow meter square wave frequency value equal to a pre programmed value stored in the memory of the TCCS the TCCS will shut off the fuel injector pulse to save the engine from detonation. This is called Hitting the Fuel cut. There is room to spare above this level in the fuel map but the TCCS cuts the fuel at this point to be sure there will be no detonation. Detonation is an uncontrolled explosion inside your engines combustion chambers. When this happens in an engine it is not uncommon to see pistons and other engine parts in the exhaust system of the car. The TCCS will never let this happen to the engine, this is why it has the safety systems like the fuel cut built into it from Toyota. Other stand alone fuel systems on the market that use a PC notebook and software to build a fuel map for your engine will allow this Detonation to happen in a heartbeat. Its not that these systems are bad it just that they are not as smart as the TCCS, they work fine in a race car that have people running the system that know exactly what they are doing. They are not for the bulk of the population who want the car to pass emissions and run predictably with all the changing conditions needed for a street car and daily driver.
Note: Pre-Ignition is not Detonation. Pre-ignition is an unwanted early explosion of the air fuel mixture in the cylinder before the spark plug was due to spark. In most cases with Toyota engines this is caused when the spark plug electrode or carbon deposits exceed 1700 deg F. When pre- ignition occurs the engines performance will fall off and the sparkplugs and pistons can become pitted or even partially melted with prolonged exposure to pre-ignition.
FUEL CALCULATIONS:
The theory behind the Lexus air flow meter upgrade for the 7M-GTE engine is to slow down the square wave frequency coming from the air flow meter into the TCCS. The square wave signal coming from the air flow meter is a key input value required by the TCCS to calculate the BASIC FUEL CALCULATION, for any of the possible engine load condition.
The total amount of fuel injected into the engine is calculated in a number of steps by the TCCS. The air flow meters square wave signal as well as RPM, air temp, coolant temp & throttle position are all calculated to determine the initial pulse width value for fuel delivery under the present conditions. This initial calculation or best educated guess is called the BASIC FUEL CALCULATION. It is used as the starting point for the amount of fuel that is injected into the engine.
When the TCCS is controlling the BASIC FUEL CALCULATION on the fly to accommodate the rapidly changing engine conditions it is using input data from the oxygen sensor. When the TCCS is LEARNING about the amount of fuel correction that is taking place under the engines operating range It is watching and learning what is taking place with the fuel requirements.
By using a system called LEARNED VALUE {Vf} or the FUEL TRIM correction system. The TCCS uses its best guess or BASIC FUEL CALCULATION plus a +/- 40% floating correction factor determined by the LEARNED VALUE Vf system to give the engine the correct required amount of fuel under all conditions. In short, a very smart and well designed system indeed.
This + or - correction amount is controlled by an active control system in the TCCS called the LEARNED VALUE SYSTEM, Vf fuel trim. Under this system the TCCS uses two types of fuel trims called the long and short fuel trims.
The LEARNED VALUE Vf system is used by the TCCS during both open and closed loop operation to fine tune the fuel control to the engine in relation to engine wear, sensor shift and other problems such as combustion leaks and intake air leaks.
This long and short fuel trim is an automatic on the fly correction system that uses the engines sensors to add or subtract fuel from the BASIC FUEL CALCULATION to keep the fuel mixture going out the tail pipe on target under the fast and slow changing engine conditions, examples: Hot, Cold, idling, redline, wear in cylinders and head, or any number of engine operation conditions.
The current amount of fuel correction the long and short fuel trims systems are adding or decreasing from the BASIC FUEL CALCULATION can be read by reading the voltage coming out of the TCCS's Vf data output terminal in the diagnostics connector under the hood of the Supra. The Vf line feeds five stepped voltage values of 0,1.25, 2.5, 3.75, 5.0 volts. Each step in voltage is an indication of the amount of fuel trim to the BASIC FUEL CALCULATION that is taking place.
LEXUS AIR FLOW METER SPECIFICATIONS:
The Lexus air flow meter is equipped with an electronic square wave Karman vortex device that is mounted to the air flow meters aluminum body with three phillips screws. The air flow meters aluminum body has two separate air passage ways through it; a large one that contains the Karman vortex generator sensor, and a smaller one that is straight through and has an adjustable flow size.
-The Karman Vortex Electronic Sensor The electronics module on the Supra and the Lexus air flow meters have numerically different part numbers but are dimensionally exactly the same size. Due to the part number difference on the electronics module on the 7M-GTE and Lexus air flow meter, I only recommend the use of the aluminum body of the Lexus air flow meter for this upgrade. The electronic module from the stock 7M-GTE's air flow meter should be mounted onto the Lexus air flow meters larger aluminum body with the three small original Phillips mounting screws.
THE LARGE CHAMBER In the large passage way through the aluminum body of the lexus air flow meter, filtered incoming air is measured with the TCCS Karman vortex measuring sensor mounted in the air flow meters body large chamber. Air travelling down this passage way is measured by the Karman Vortex generator sensor, therefore this air is known to the TCCS ECU as the KS {square wave} signal. The volume of this chamber is fixed in size but is much larger than the stock 7M-GTE air flow meters main measuring passage way.
I may refer to this chamber as the measured CHAMBER, or Large chamber. Only air that passes through the main measured chamber is accounted for by the TCCS engine control computer.
THE SMALL CHAMBER The Lexus meter also has a smaller adjustable capacity passage way. The adjustable passage way allows a percentage of the fresh filtered air that is not measured by the TCCS engine control computer to go directly into the engine. The volume amount of this direct in air can be adjusted by a custom Sonic air screw located in the center of the this small chamber. The adjustment screw in this chamber can be set to any position allowing the chamber to be from 100 % open to 85% closed in the chambers air flow.
As the filtered incoming air that passes through this smaller chamber does not come through the larger measuring chamber this air is an unknown portion of the total filtered induction air. Any air that passes this chamber is not known by the TCCS engine control computer because the Karman vortex sensor did not measure it. It took the back door in you might say.
Example A: If this small chamber would be plugged off or adjusted to a fully closed position; this would cause all of the filtered induction air to be sucked through the measuring chamber instead of through both the measured chamber and the small direct in chamber. If all the induction air is sucked through the measured chamber this would cause the Karman vortex sensor to measure all the induction air and report this to the TCCS for use in the BASIC FUEL CALCULATION. Closing the small chamber caused an increase in the square wave frequency for the same amount of total filtered induction air volume. The TCCS would see the air and increase the amount of fuel used in the BASIC FUEL CALCULATION.
Example B: If the smaller direct in chamber is opened up to 100 percent of its size this would allow some of the air that was forced through the large measuring chamber to bypass and go directly past the sensor. This would cause the TCCS to see less air volume and reduce the amount of fuel in the BASIC FUEL CALCULATION.
This back door air causes the electrical square wave signal produced in the large chamber by the karman Vortex sensor to slow down in frequency by a percent relative to the amount of air that sneaks into the engine through the small chamber. You might say it starts to lie to the engine or withholds information.
THE LEXUS ADVANTAGE STARTS HERE:
When this larger volume Lexus air flow meter is installed on a Supras 7M-GTE engine control system this causes the unknowing stock Supra TCCS engine control computer to think that less air is entering the engine than actually is. The amount of physical air your engine is using under standard conditions is still the same regardless of which air meter is plugged into the system. The TCCS does not realize this!
Example: A Man consumes the same amount of air when sitting in a chair breathing through his mouth as he does breathing through his nose. The amount of air used in this condition does not change if the persons mouth is 70 % open or 20 % open. From this example it follows that the difference to your Supra engine control system from the change in air flow meter size is; The Lexus air flow meter lies to the TCCS engine computer about the volume of air coming into the engine.
The Lexus flow meter causes the TCCS to see a slower square wave signal from the air flow meter than the stock air flow meter would send to the TCCS. This tells the TCCS that there is less air than there actually is coming into the engine but in reality there is not less air coming in. The air flow meters function is to measure the air coming into your engine. When we change the size of the air flow meter body we are in actual fact changing the scale of the air reading that is sent to the TCCS.
THE FIRST LIE:
The TCCS engine computer responds to this less measured air condition and reduces the amount of fuel it puts into the engine by adjusting the fuel injector pulse width to inject less fuel. Because there is not less air coming into the engine, this less fuel adjustment to the BASIC FUEL CALCULATION makes the engine run leaner than the engine is designed to for a very short time, a few milliseconds. Because the TCCS is a learning fuel system it sees that it has set the mixture too lean and uses its built in adaptive systems called, the Vf Learned Value long and short fuel trim systems to compensate for its error.
Rather than simply discarding the incorrect air flow reading from the Lexus air meter, the TCCS will continue to correct for the detected mixture error using the long and short Vf fuel trims. This is how we take advantage of the TCCS and upgrade the fuel map of the system. If the TCCS just corrected the incorrect air flow reading this upgrade would never work.
The actual amount of the fuel mixture adjustment correction made by the TCCS's long and short fuel trims can be determined by using the Vf data output. The prime function of the Vf voltage data is to display what the condition of long and short fuel trim levels is.
The Vf data line emits 5 stepped voltages in the range of 0, 1.25, 2.5, 3.75, 5.00 volts. The TCCS will always output one of the five voltages to the Vf terminal in the diagnostics connector under the hood. The voltage is measured at anytime between the E1 and Vf pins in the diagnostics connector when E1 and T1 are not shorted. Remember that the voltages are stepped in 5 levels as mentioned above! Depending on your car you may see 3.5 volts rather than 3.75 volts, this is normal and you can ignore the difference in the voltages.
The following is an example of the Vf voltage reading compared to the fuel correction required to make the fuel mixture correct:
[0 volts] Maximum Lean, reduction of the fuel mixture from the BASIC FUEL CALCULATION
[1.25 volts] Minimum Lean, reduction of the fuel mixture from the BASIC FUEL CALCULATION
[2.5 volts] No correction at all to BASIC FUEL CALCULATION
[3.75 volts] Minimum Rich, increasing the fuel mixture above the BASIC FUEL CALCULATION
[5 volts] Maximum Rich, increasing the fuel mixture above the initial calculation
NOTE: THE TCCS IS ALWAYS MAKING THE AIR/FUEL MIXTURE CORRECT FOR YOUR ENGINE. THEREFORE THE Vf VOLTAGE INDICATION SHOWS YOU HOW HARD THE TCCS IS WORKING TO MAKE THE AIR/FUEL MIXTURE CORRECT.
Remember that {0 volts Maximum Lean} does not say that the car is running lean! It is saying is that the TCCS is leaning the BASIC FUEL CALCULATION to make the mixture perfect for the current conditions. There was too much fuel calculated for the BASIC FUEL CALCULATION causing the engine to run RICH for a short time so the TCCS is reducing the fuel amount from BASIC FUEL CALCULATION. The 0 voltage LEAN is a very safe or normal reading, it is telling you that there is plenty of room to add fuel, lots of correction reserve left. Many stock cars running at high altitude will show a 0 volt condition, high altitude is less air for the engine, so the TCCS cuts back some of the fuel to compensate for the to rich mixture.
For more information see the text file at the FTP site on Vf output file name TNSTCCS2.txt.
This Vf information can be read at anytime from the Vf terminal in the diagnostics block {close to the battery}. A volt meter can be used to read the Vf data, but there is a better way! Last year after I supplied the supras list with my posting explaining the Vf line information, Jeff Montigny from the club followed through with a custom home built electronic meter that reads the Vf line voltages, the Montigny meter as it is called lights up 5 coloured LED's to show the correction taking place. See the example below to read about the meters five LED lights and the Vf line voltages:
Red LED [0 volts] Maximum Lean, reduction of the fuel mixture Yellow LED [1.25 volts] Minimum Lean, reduction of the fuel mixture Green LED [2.5 volts] No correction at all to initial fuel calculation Yellow LED [3.75 volts] Minimum Rich, increasing the fuel mixture Red LED [5 volts] Maximum Rich, increasing the fuel mixture
THE SECOND LIE {not really a lie, just not really the whole story}
Now that we have lied once to the TCCS about the actual air volume coming into the engine, and the TCCS believes without question that the air meter readings are always correct, we will now re-balance the first lie with a second lie. Not really a lie, we are just withholding information from the TCCS, what it does not know will not hurt it.
This second fib is a small one, changing the fuel injector size to a larger injector so the TCCS will no longer need make the short and long fuel trim corrections. The increased injector size allows more fuel to be injected at any given pulse width. (Remember that the TCCS leaned out the mixture because we caused a fib about the actual air volume coming into the engine.) By increasing the injector size to a larger injector we are allowing the correct amount of fuel to be injected into the engine with the short injector pulse width caused by the Lexus air flow meters false reading.
With the larger injector the TCCS will not see any lean condition and respond by correcting the error with the long and short fuel trims. The TCCS will not know the difference because it will see that everything is normal. The short fuel injector pulse width combined with the larger injector will inject the correct amount of fuel into the engine allowing for normal drivability.
THE ADVANTAGES: Some of the advantages to running with the Lexus air flow meter are as follows:
1. INCREASED FUEL CUT LIMIT The fuel cut system on the 7M-GTE engine is activated by the square wave signal coming from the air flow meters electronic vibrating mirror. When the square wave signal hits a programmed level the TCCS cuts the fuel off. The higher the air flow the faster the square wave signal. Due to the larger size of Lexus air flow meter, this large size slows down the square wave signals frequency to a lower level allowing for more boost and more maximum horse power. 2. LESS AIR FLOW RESTRICTION TO TURBOCHARGER & ENGINE As HKS has achieved with the VPC system, removing the restriction of the air flow meter helps the turbo respond faster and also allows for free breathing of the engine. The stock air flow meter is sized right for the stock CT26 turbochargers air flow requirements but as you increase the boost pressure beyond the stock setting and upgrade the exhaust system and the turbocharger you are allowing your engine to suck more air through the air flow meter. As this air volume increases the restriction from the air flow meter becomes more and more of a problem. 3. ALL FEATURES OF THE STOCK FUEL SYSTEM FUNCTION AS NORMAL Strong stable idle, improved mid range torque and high end performance without any drivability concerns at the higher boost pressures. 4. FUTURE UPGRADE PATH The use of other piggy back fuel computers such as HKS F-con and VPC can be used. Also TECHTOM upgrade cards and re-mapping can be done to yield a killer horsepower system without the need of additional injectors and AIC's. 5. FULL ADJUSTABILITY OF THE LONG AND SHORT FUEL TRIM SYSTEMS When the Lexus air flow meter is used on the 7M-GTE it must be used in conjunction with the custom air screw and the custom bolt on adjustable fuel pressure regulator that I have tested and developed for this upgrade. The adjustable fuel pressure regulator and air screw are used to allow the BASIC FUEL CALCULATION to be adjusted as close to the factory mixture setting that was required with the stock air flow meter and factory injectors. When the system is re-balanced the TCCS will display factory Vf line voltages allowing the engine to respond and run just as it did when it left the Toyota plant in Japan. The upgraded system will not be maxed out to the full rich or the full lean fuel trim corrections. This often happens with piggy back fuel systems that are not running correct programming.
CONCLUSION (Dyno tests on 1982 Supra GTE with 7M-GTE engine) The Hp and Torque numbers that I have posted to the Sonic FTP site are:
339 HP at the rear wheels 398 Ft/lbs of torque @ 14.5 psia of boost.
These HP and Tq numbers were achieved with the only fuel system upgrade being this Lexus fuel upgrade, custom air screw and adjustable FPR and big injectors.
This 7M-GTE engine has factory assembled bone stock internals. The intercooler is also bone stock 1989 MA-71 supra turbo. This engine has travelled over 120,000 KM's since it left the Toyoda engine plant in the red MA-71 that it was installed into.
The only modified parts were:
HKS Sport Turbo upgrade HKS EVC II HKS Super Power Flow HKS MA-67 turbo exhaust system
These runs were not made at the maximum boost pressure that I have run my engine but at with this fuel upgrade but I feel this is a very safe boost level for this upgrade.
This winter I will be installing an upgraded HKS intercooler, I will return to the Dynojet in the spring of 1997 with the new intercooler.
I hope this tech note helps with your understanding of the TCCS system used on the 7M-GTE engine.
Written by Reg Riemer
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