View Full Version : FAQ Submission: FI and other Toyota Jargin by Luni

12-01-2004, 11:05 PM
By Luni

The turbocharger is a centrifugal compressor driven by the otherwise-wasted energy in the exhaust stream. It is a 2 chambered housing with a shaft through the center extending into both chambers. A turbine wheel is mounted on one end of the shaft and is in the exhaust stream, and an impeller wheel is mounted on the other end. That is the compressor end, and it is connected to tubing that goes to the intercooler, and then to the throttle body. A turbocharger is really a very simple device, and as long is it regularly fed clean , high quality oil from the engine lube system, and allowed to cool down before engine shutdown, will last nearly as long the engine itself.

There are two alternate paths for the exhaust flow at the turbo. One is across the turbine, and the other is out the wastegate, allowing it to bypass the turbo. Since more energy at the turbo means more air to the engine, which means more energy to the turbo, which in turn means more air to the engine, which means...well, I think you get the point. The wastegate is necessary to limit the airflow output from the turbo.
The wastegate isn't simply open or closed; it modulates to maintain very precise control over the turbo's speed and output.

Compressors are pumps, and pumps create flow. When the turbo creates more airflow than the engine is consuming, then the air becomes pressurized. So boost pressure will rise and fall as the turbo output increases and decreases. Thats why the wastegte controls the speed and airflow of the turbo. And pressure and flow are directly related. That means you can not get "more flow at the same pressure..."

The wastegate actuator is simply a can with a rubber diaphragm on one end, and 2 ports with hose fittings on the front end. Looking into the engine compartment form the driver's side, it can easily be seen just to the right of the turbo compressor inlet. The hose on the left is connected to the turbo, and the hose on the right is connected to the T/VSV. (more on that later) There is a spring that holds the diaphragm in place that has a yeild value of about 7 psi.. As pressure builds in the turbo, air begins to fill the actuator and pushes against the diaphragm. When the pressure exceeds the spring value, ~ 7 psi, the actuator moves out, pushing a rod, and opening the wastegate.

(Turbocharger Vacuum Switching Valve) is a "factory-installed boost controller". It is simply a solenoid-operated valve that, when energized (open) allows air to escape from the actuator, lowering the pressure in the actuator, and allowing the wastegate to modulate closed. This vented air actually flows back into the intake airstream between the airflow meter and the turbo intake so it does not distort the ECU's air/fuel ratio calculations.

The T/VSV is a normally closed-energized open valve. The ECU will energize (open) it whenever you boost IF 1) engine coolant temps are up to normal , and 2) ambient (intake) air temps are above ~ 32 deg F. (There may be some variation with that number). If the T/VSV is open (high boost mode) and the ECU gets a signal from the knock sensor, it will de-energize (close) the T/VSV. Likewise, if there is an over boost signal from the boost pressure sensor, it will de-energize the T/VSV as part of the "fuel-cut" sequence.

NOTE: Unless you have an aftermarket boost controller, disabling the T/VSV will lock you into low-boost mode!! It WILL NOT increase boost.

The normal range of max boost ranges from 7.1 to 11.8 psi, according to the Factory Repair Manual. Low boost problems are almost always a result of some problem in the boost control system and rarely with the turbo itself..

The boost pressure sensor is simply a pressure transducer that monitors manifold pressure and reports it to the ECU as a voltage value. If the voltage exceeds about 4.4 volts (~12 psi on '91, 92' and early 93's, ~16 psi on late 93's and up) the ECU initiates the fuel-cut sequence. It de-energizes the T/VSV to lower boost, retards ignition timing, and restricts fuel delivery by limiting the injector cycle. The "check-engine" light will come on for about 20 seconds, and a code 34 will be stored in the diagnostic memory. You will be in "limp mode" and unable to boost again until you shut off the engine and restart it. No other reset is required to return to normal operation. You do not have to pull any fuses or disconnect the battery (Internet legend!)

For a complete schematic diagram of the turbo and boost control system, go here:

Click on "Boost Control"

Since the rate and amount of airflow to the wastegate actuator control's its operation, we can increase the boost by either restricting the airflow into the actuator chamber, or by increasing the bleed rate of the air escaping the actuator. Boost controllers range from simple orfice plugs inserted into the hose connecting the turbo the the actuator, to complex multi-valve electronically operated devices, but again, the all do the same thing: they manipulate the amount of air (pressure) in the actuator.

Since the FC response is programmed in at ~ 12 psi*, you must somehow eliminate it or alter it to boost above ~12 psi. Fuel-cut is initiated when there is a 4.4 volt signal to the ECU from the sensor, so ALL fuel cut defeat (FCD) system either prevent that from happening, or delay it . Some methods simply eliminate FC completely by preventing any thing over 4.3 volts from ever reaching the ECU. This includes the Greddy BCC, the Zener diode, disconnecting the hose, etc. The HKS FCD is an adjustable FCD that has one setting that raises fuel cut to ~17 psi without eliminating it.

*(late 93's and later have FC set at ~ 16psi from the factory)

Here is some further information about the HKS FCD (this one is installed on an MR2):


Or a member from the MR2 Board named BillWOT has designed a simple, fully adjustable FCD that allows you to set FC at any value you want, from stock up to the system max of ~ 17.5. It will cost about $8 for parts and should take less than an hour to build and install. No, I won't build you one.

Here is a discussion and instructions for the $8 BlackBox FCD:
*note that installation is on an MR2 and you will have to modify the instructions to fit the location of the ECU on a Celica Alltrac or your Hybrid Swap Celica*


Car manufacturers measure airflow into an engine with sensors. It lets the ECU make a decision for the air/fuel ratio. The 3SGTE has what is called an AFM or Air Flow Meter. It is a silver box type chamber attached inline on the intake tube.

Another type of sensor to measure air intake in an engine. The MAP or Manifold Absolute Pressure sensor measures air pressures in the intake manifold, letting the computer make a decision for the air/fuel ratio. The 3SGTE is strange in that it has an AFM and a MAP sensor (however on the 3SGTE the MAP isnt called MAP, its called the Turbo Pressure Sensor). On the 3SGTE the MAP sensor is used to measure positive turbo pressure in the intake manifold. It serves 2 purposes. It gives a reading to the factory boost gauge, and it sends a reading to the ECU. As described above, the ECU will initiate Fuel Cut if boost exceeds the preprogrammed values. This MAP sensor sends those values to the ECU to make that decision. On a 5SFE or other engine, the MAP serves exactly the same purpose as the AFM on the 3SGTE.

TVIS or Toyota Variable Induction System is a system installed between the intake manifold and the head. It consists of a metal plate that has vacuum operated metal butterflies on it. Below 4500 RPM it is designed to keep the butterfiles in the path of the air entering the head. What it does is increase backpressure in the system, effectively raising low end torque. Above 4500 RPM, a vacuum signal tells the plates to move to the side where they are no longer obstructing flow, thus letting the engine breathe like it needs to at high RPMs. Its an effective way to make high range HP and low end Torque. After 300 or so HP it becomes restrictive, even at high RPM, and is usually in the best interest of the enthusiast to remove.

I give props to BillWOT because I stole the majority of this FAQ from him off the MR2 board. The information contained within is beneficial to the Celica community and he worded it in such a way to make it very understandable so I changed only what needed to be changed to make the words apply to a celica too. Thanks to Bill. And thanks to everyone else who reads this.

12-01-2004, 11:06 PM
And by Nuke:

some common problems with a turbo charged engine:

Boost Creep: An unwanted operating condtion that occurs when the engine overwhelms the wastegate. When this happens, the wastegate cannot move enough air to prevent the turbine blade from moving any faster and therefore the system can't maintain the preset boost level. This occurs because of 2 reasons:

1- An improplerly sized wastegate for that specific engine

2- A badly designed downpipe that doesn't allow teh wastegate to function to it's maximum capabilities.

Overboost: This term is used to describe an engine with a faulty or less than ideal boost control system. When a car overboosts it overshoots it's desired set psi. This usually happens as the turbo is spooling. It overshoots the set pressure and then drops back to the preset. This is usually an indication of:

1- A cheaply made boost controller
2- Long vacuum hosing between the pressure reference (the nipple on the turbo) and the wastegate actuator
3- A bleed or a small hole in the boost control system between the pressure reference and the wastegate actuator

fuel cut or boost cut An engine error condtion trigged by the stock 3sgte ECU. This condtion occurs when ECU sees excessive pressure in the intake manifold. And is described in detail above (Luni420 is the bomb)!

It's important to note that when fuel cut occurs, a check engine light comes on. Also, basic bolt ons (intake / downpipe/ b-pipe/ cat-back) can on some turbo cars cause fuel cut even without altering the stock boost control system.

Note: Be careful when using nitrous oxide on a turbocharged car. Nitrous may cause boost creep. This may also lead to fuel cut. Fuel cut + n2o = severe lean conditions in the engine and can be destructive to the car.

Missfires: A missfire occurs when the ignition system is unable to spark the gap at the sparkplug. On a turbocharged car, this can occur when the pressure is increased from stock settings. By doing so the car will seem to run rich and may back fire. It will also loose alot of high rpm power since it is more likely to misfire at higher revs. To remidy this problem the spark plug gap should be reduce when the pressure is raised, cars running n2o or water injection should further reduce the plug gap to accomodate for the desner (and harder to burn) mixtures.

Note: Many 600+hp supras have seen as much as 30 wheel hp gains from plug gap tuning. The desired plug gap is the highest gap the car can run without a misfire occuring...