Basics Of Fuel Injection
This section will give you a basic understanding of the TCCS (Toyota Computer-Controlled System) functions.
 
General Description Of The TCCS EFI Block Diagram
TCCS Block Diagram  ESA (Electronic Spark Advance)
EFI (Electronic Fuel Injection) Main Components of ESA And Their Functions
Main Components of EFI And Their Functions ESA Block Diagram
 
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TCCS

The TCCS uses an ECU (Electronic Control Unit) with a built in microprocessor. The ECU stores such data as the optimum fuel injection duration (the duration is the length of time the injectors are held open, the longer the duration the more fuel that is injected), injection timing (when the injectors are opened), ignition timing, and the correct idle speed for various running conditions. The ECU is feed input from various sensors and then chooses the data stored that is suitable for the current engine conditions, and then sends the most suitable signals to the actuators. The TCCS can be divided into three main sections, the sensors, the ECU and the actuators.
 

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TCCS Block Diagram
 
TCCS Block Diagram
 
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EFI

In an Electronic Fuel Injection system fuel is delivered via fuel injectors. The system works by monitoring various sensors which inform the ECU how much fuel needs to be delivered. The EFI system in the ST185 uses a high pressure fuel pump and a fuel pressure regulator mounted in the fuel rail to keep the fuel pressure in the rail at a constant pressure. On problem with turbocharged cars is that the boost has a negative effect on the pressure when the injectors open. This problem is addressed by the use of fuel pressure regulator that increases fuel pressure when the boost pressure increases. A vacuum line runs form the intake manifold to the fuel pressure regulator, when there is boost pressure in the intake manifold, the fuel pressure regulator will increase fuel pressure by 1 psi for every 1 psi increase in boost.
 

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Main Components of EFI And Their Functions
 
 
AFM (Air Flow Meter) Ignition Switch (Starting Signal)
TPS (Throttle Position Sensor) Turbo Pressure Sensor
Water Temperature Sensor Knock Sensor
Intake Air Temperature Sensor Oxygen Sensor
Vehicle Speed Sensor Air Conditioner Switch
Distributor Cold start Injector
Fuel Injectors ECU
 
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Air Flow Meter
 
The air flow meter detects intake air volume so the ECU can determine the basic injection duration, and the basic ignition advance angle. The AFM uses a potentiometer to detect air volume, the potentiometer is attached to a flap in the AFM that opens more as air volume increases. The AFM operates on a 5 volt supply from the ECU.
 
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Throttle Position Sensor
 
The TPS is mounted on on the throttle body. It converts the throttle opening angle into a voltage, and the ECU uses this information to detect whether the engine is idling or under heavy load. It also detects engine acceleration by detecting the speed at which the throttle opening angle changes. The TPS uses an idle contact to in inform the ECU when the throttle is completely closed (idle) and a variable resistor, which linearly converts the throttle opening angle into a voltage signal. The TPS operates on a 5 volt supply from the ECU.
 

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Water Temperature Sensor

The Water Temperature Sensor informs the ECU of the coolant temperature, which plays a role in ECU's adjustment of injector duration and ignition timing. The sensor itself varies it's resistance with temperature, and as such the ECU knows the coolant temperature at all times based on the voltage returned to it by the Water Temperature Sensor. 
 

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Intake Air Temperature Sensor
 
The Intake Air Temperature Sensor works in much the same way as the Water Temperature Sensor, varying it's resistance with air temperature, which informs the ECU of the incoming air temperature. This sensor is located within the AFM.
 
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Vehicle Speed Sensor
 
The Speed Sensor informs the ECU of the vehicle's speed.
 
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Distributor
 
The Distributor consists of three signals, that can be seperated into two categories.

First G1 and G2 signals, which sense the standard crankshaft angle, allowing the ECU to determine the position of each piston and thus determining injection timing, which cylinder is to be fired,  and ignition timing.

The Ne signal informs the ECU of engine speed and crankshaft angle.
 

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 Fuel Injectors

Fuel is injected into the intake port of each cylinder before the intake stroke in accordance with injection signals from the ECU, via the Fuel Injectors. A fuel injector is mainly made up of a needle valve, a plunger and a solenoid. By applying voltage to the injector the solenoid engages and opens the injector allowing fuel to be delivered.

Fuel Injector
 
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IGNITION SWITCH
 
The Ignition Switch (Starting Signal) determines whether or not the engine is starting.
 
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Turbo Pressure Sensor
 
This sensor is responsible for informing the ECU of the turbocharging pressure in the intake manifold, and also feeds the signal for the stock turbo pressure gauge in the instrument cluster. The ECU uses this signal to determine if an over boost situation occurs. As of date, I have not been able to find out if the ECU uses the signal from Turbo Pressure Sensor to aid in the determination of other parameters, such as fuel injection duration and ignition advance.
 
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Knock Sensor
 
A knock sensor is used in the ST185 to allow the ECU to detect knocking (detonation or pre-ignition). The sensor is screwed into the block and it listens for knocking, if knock is detected, the ECU will retard the timing to save the engine. There are many theories as to whether the ECU does anything else, and also as to how much the timing is retarded. My personal belief is that when knock is detected the ECU retards timing one degree at a time for a certain number of degrees until there is no more knock, and then will increase it until knock is detected, and then lower again, producing a cycle, however if knock does not cease within a certain amount of degrees of retard, it will retard it back to base, resulting in a loss of power feeling.
 
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Oxygen Sensor
 
The O2 sensor is responsible for informing the ECU of the density of oxygen in the exhaust gases. By knowing the oxygen content of the exhaust the ECU is able to determine the air-fuel mixture. The ECU uses signals from the O2 sensor as one of the parameters to determine injection during what is called closed loop mode. The ECU ignores the O2 sensor's signal during open loop mode.

Closed loop is used to keep the engine as close to a stoichiometric (14.7:1 air-fuel) ratio as possible, and is used when the engine is in low load situations, i.e highway cruising.

Open loop is used at WOT (wide open throttle) when the engine is under high load, i.e accelerating, with throttle angle above a certain percentage. Once in open loop the O2 sensor is ignored and a fixed fuel map is used by the ECU. This fuel map is usually around 13:1 air-fuel ratio. The O2 sensor is also ignored when it is cold.

The O2 sensor is easily contaminated, and as such leaded gasoline should never be used, as well as silicone sealants/gaskets that are not O2 safe.
 

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AIR CONDITIONER SWITCH
The A/C switch senses whether or not the A/C compressor is on or off.
 
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COLD START INJECTOR
 
The Cold Start Injector is used to inject extra fuel into the intake air chamber during engine cranking to improve stability. The cold start injector is turned on when the coolant temperature is around 20oC or below, and is controlled by the ECU until the coolant warms up to around 40oC.
 
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ECU
 
The ECU first determines the basic injection duration based on the intake air volume signal and the engine rpm signal. It then determines the injection duration actually required by the engine by adjusting the basic injection duration based upon the signals from various engine sensors, about the operating conditions of the engine. At the same time the ECU determines the basic ignition advance angle from engine speed and the air intake volume, and adjusts this angle depending on signals from various other sensors.

The ECU sends the appropriate signals, based on various sensor inputs, to the igniter. The igniter is responsible for shutting off primary current resulting in the spark plugs igniting and sends an ignition conformation signal back to the ECU after ignition.
 

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EFI Block Diagram
 
EFI Block Diagram 1
EFI Block Diagram 2
 
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ESA (Electronic Spark Advance)
 
In order to maximize engine power, the air-fuel mixture must be ignited when the maximum combustion pressure occurs, which is about 10o after TDC. However, the time from ignition of the air-fuel mixture to the development of maximum combustion pressure varies depending on engine rpm and the manifold pressure, ignition must occur earlier when engine speed is higher and later when engine speed is lower. For the ST185, boost pressure also influences the point at which ignition should occur. The ESA system provides the engine with nearly ideal ignition timing. The ECU determines ignition timing from its internal memory, which contains optimum ignition timing data for each engine condition, and then sends the appropriate signals to the igniter.
 
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Main Components of ESA And Their Functions
 
 
AFM (Air Flow Meter) Ignition Switch (Starting Signal)
Water Temperature Sensor Distributor
TPS (Throttle Position Sensor) Igniter
Vehicle Speed Sensor Knock Sensor
Air Conditioner Switch ECU
 
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ESA Block Diagram
 
ESA Block Diagram
 
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 This page was created by Dennis Heath.
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Please note that I am not a mechanic by trade, and that any information offered on this web page is free and without guarantee. Should you choose to perform any of the procedures listed on this site, you will be doing so of your own free will, and I will not be held responsible or liable for any damages that might occur from using information obtained here.