Fuel Injection

Fuel injection is a system for mixing fuel with air in an internal combustion engine. It has become the primary fuel delivery system used in automotive petrol engines.


 1.        First we listen to the injectors as the engine is idling. Next we use a stethoscope, vacuum line or long screwdriver. Be careful of moving parts. They should sound like a sharp tap, not a dull thud or nothing.

This is a crude test to see if they are being actuated and are opening.

OK ✓ Not OK ..........

Can you get to all the injectors? Yes✓ No .........

Comments: There was a Small tapping noise coming from the vacum line when it was held aboove the injectors

2.       To Check the voltage to the injectors when idling or Key On. This makes sure you have battery voltage to the injectors so they can work.

Record battery voltage: 12.47
Record voltage at each injector you can get to by back probing. Be careful to not puncture or damage wiring.

Cyl #1	Cyl #2	Cyl #3	Cyl #4	Cyl #5	Cyl #6
14.13v	14.14v	14.12v	14.13v	-	-	Volts

3.        With engine idling, watch injector firing by using an LED tester or test light (with normal incandescent bulb). Hook up test light and connect tip to pin that has back probed connector to injector -. As the injector is grounded by the ECM to fire, the test light should also be grounded to fire, and will flash.

Cyl #1	Cyl #2	Cyl #3	Cyl #4	Cyl #5	Cyl #6
✓	✓	✓	✓	-	-	Tick if flashes OK

4.        With engine idling, watch injector firing by using a multi-meter set to read % (duty cycle). Record the readings for each cylinder at idle in the boxes below.

       

Cyl #1	Cyl #2	Cyl #3	Cyl #4	Cyl #5	Cyl #6
5.2%	5.3%	5.2%	5.2%	-	-	Duty cycle %

5.        With the multi-meter still set to read % (duty cycle), accelerate the engine with short, fast throttle openings (don’t over-rev or damage the engine please), and note in the boxes below the maximum % reading you can get on the multi-meter: note the RPM.

Cyl #1	Cyl #2	Cyl #3	Cyl #4	Cyl #5	Cyl #6
14.7%	14.4%	14.4%	14.5%	-	-	Duty cycle %

RPM + - 2000

6.        Set the multi-meter to read Hz, and with the engine idling, record the readings for each cylinder in the boxes below:

Cyl #1	Cyl #2	Cyl #3	Cyl #4	Cyl #5	Cyl #6
0.009	0.009	0.011	0.009	-	-	Hz

7.        With the multi-meter still set to read Hz, increase the engine RPM (don’t damage the engine), and watch how the Hz changes. Record your highest reading in the boxes below: Take the readings at the same RPM as you used in question 5.

Cyl #1	Cyl #2	Cyl #3	Cyl #4	Cyl #5	Cyl #6
0.022	0.020	0.021	0.20	-	-	kHz

RPM + - 2000

The Injector

­A fuel injector is nothing but an electronically controlled valve. It is supplied with ­pressurized fuel by the fuel pump in your car, and it is capable of opening and closing many times per second.

Inside a fuel injector

When the injector is energized, an electromagnet moves a plunger that opens the valve, allowing the pressurized fuel to squirt out through a tiny nozzle. The nozzle is designed to atomize the fuel -- to make as fine a mist as possible so that it can burn easily.

A fuel injector firing

The amount of fuel supplied to the engine is determined by the amount of time the fuel injector stays open. This is called the pulse width, and it is controlled by the ECU.

Fuel injectors mounted in the intake manifold of the engine

The injectors are mounted in the intake manifold so that they spray fuel directly at the intake valves. A pipe called the fuel rail supplies pressurized fuel to all of the injectors.

In this picture, you can see three of the injectors. The fuel rail is the pipe on the left.

In order to provide the right amount of fuel, the engine control unit is equipped with a whole lot of sensors. Let's take a look at some of them.
(http://auto.howstuffworks.com/fuel-injection3.htm)

Inputs/Outputs Report

 In this report, I will be explaining the function of the different sensors. Also I will detail how this system relates to a closed loop circuit and why. There are seven inputs I will be discussing and also three outputs which directly relate to these inputs, which will also explain the closed loop theory.

The  sensor inputs I will be discussing are the Coolant Temperature Sensor (ECT), Throttle Position Sensor (TPS), Oxygen Sensor (O2), Manifold Absolute Pressure Sensor (MAP), Mass Air Flow Sensor (MAF), Camshaft Position Sensor and the Crankshaft Position Sensor. First of all, it should be stated that all of these sensors are electrical switches which are linked to the ECU and send information which contribute to the adjustment of engine output at any given time.

The Coolant Temperature Sensor, is located in the coolant passage just before the thermostat, monitors just what it suggests, the coolant temperature of the engine. This sensor is a thermistor, which is really a resistor, and depending on the temperature of the coolant in the engine, changes the resistance of the switch which therefore changes the voltage output to the ECU. For example, if the temperature of the coolant increases, the resistance of the switch decreases and the voltage output will increase. This sensor contributes to the fuel efficiency of the engine. A basic reading from this switch would be about 2-3k ohms at 20⁰C, this will change due to the temperature.
When coolant is cold resistance through the sensor is high and less voltage can pass, but once coolant properly warms up resistance through the sensor is reduced and more voltage can pass.

Resistance	0.95 kΩ
Voltage, engine cold	3.3 V
Voltage, engine properly warm up	1.3 V

The Throttle Position Sensor, located externally on the throttle body, senses the position of the throttle butterfly and the rate of throttle opening.It measures the position of the throttle valve, whether it’s wide open or closed and sends it to the ECU.
This sensor is a variable resistor that’s resistance changes as the throttle butterfly opens and closes. The more the throttle butterfly opens, the more acceleration applied to the engine which will mean that the engine will need to alter fuel output, controlled by the ECU. Generally when testing this sensor, at closed throttle the reading should be approximately -1.25volts and at wide open throttle should read approximately 5volts, as specified by the manufacturer.

Resistance	0.54 kΩ
Voltage, engine idle / throttle close	0.6 V
Voltage, wide-open throttle	1.8 V

The Oxygen Sensor is part of the emission control system as it plays a big part in keeping the air fuel ratio as ideal as possible to restrict excess fuel being emitted as exhaust gases. Also, because of this, it is expected to find this sensor mounted in the exhaust manifold. This sensor is able to measure the amount of unburnt gases in the emissions, a lean mixture will give a reading of approximately 0.1volts and a rich mixture will read approximately 0.9volts. This sensor is one of the most important in keeping an engine fuel efficient and is the main source of feedback for a closed loop circuit.

The Manifold Absolute Pressure Sensor is mounted on the intake manifold and monitors the pressure in the manifold vacuum. When the pressure changes the sensor will change its voltage output to the ECU for adjustments to be made. The reading of the sensor will, again, change depending on the vacuum, for example, a reading of 0.5-1.5volts means there is a high vacuum and low pressure which will suggest that the vehicle is idling or decelerating. Whereas a reading of 3.0-4.5volts means there is a low vacuum and high pressure which suggests that the vehicle is accelerating hard or perhaps there could be a mechanical fault.

The Mass Air Flow Sensor measures the air entering the engine at any given time.It Measures the quantity of air flowing to the throttle body and sends it to the ECU There are different types of these sensors but the one to be discussed currently is the hot wire air flow sensor. This works by air passing by a hot element and cooling this element, which then generates more voltage to maintain the heat. The voltage increase is how this is measured. Output at idle can range from 0.4-0.8volts whereas at wide open throttle the voltage will generally be around 4.5-5volts.

Now, the Camshaft Position Sensor is positioned either directly on or next to the Camshaft. This sensor picks up the motion of the magnetic field generated by the movement of pins on the camshaft. The different speeds this camshaft turns will allow the magnetic field to fluctuate which in turn will alter the speed of the engine. This sensor is used with the Crankshaft Position Sensor to ensure correct ignition timing as well as operation and performance of the engine. 

The Crankshaft sensor is made out of 3 segments, centre part is a magnet, and the other 2 are sensors. Magnetic field is induced between the sensors and the magnet, as the magnetic field is broken, pulse signal are produced. These pulses are send to the ECU to determine the position of the pistons. The ECU then calculates the engine speed and controls ignition timing. But if the knock sensor detects detonation the ECU will retard the ignition timing up to when the detonation is ceased. It measures the RPM of the crank-shaft and the position at which the pistons are at, and sends it to the ECU.

As the seven inputs have now been discussed, it is only fitting to move on to the three actuator outputs selected for this report. The spark plugs, the fuel injectors and the Variable Valve Timing with Intelligence ( VVT-i) system.

Firstly, the spark plug, a small plug fitted into the cylinder head of the engine. The number of spark plugs used on an engine will depend upon the number of cylinders this engine will have. Spark plugs use a ceramic insert which isolates the high voltage to the end of the electrode making sure that the spark is only generated at this point. If the spark were to be created anywhere else it would cause a massive fault with the spark plug and will need replacing. The spark plug must be properly insulated so that the voltage generated can jump the gap, be conducted into the engine block and be grounded. If the gap of the spark plug is too great, it could cause the voltage to become weak or non-existent. Now spark plugs in the engine are used to ignite the air fuel mixture in the combustion chamber. This mixture is compressed and when ignited causes an explosion which pushes the piston down at a great force. The spark can range from  400,000-1,000,000volts each.

Second, the Fuel Injector, sits on the fuel rail of the engine and delivers fuel to be mixed with the air in the combustion chamber. Each injector will have an electrical plug to be attached to it, which is also attached to the ECU. The fuel however is pushed into the injector and when the pressure is at a certain point, the spring will lift the pintle off its seat and cause a passage way for the fuel to be sprayed into the chamber. Now, there are no specifications from the manufacturer on what an injector should read but if testing all these injectors and one voltage is signal is significantly different from the others then there is more than likely a fault with that particular injector.

Lastly, the VVT-i system. This system maximises engine performance by making the air intake and exhaust valves as efficient as possible. This system is able to adjust overlap time between when one valve shuts and another opens, which ensures power when you need it and optimal fuel efficiency. From this will also create a cleaner exhaust as less unburnt gases will be emitted.

Now that both the inputs and outputs have been explained, this can all be related to a closed loop circuit. A closed loop circuit is when a control system is able to get feedback. In this case, the ECU is able to receive information in order to alter faults in the engine where ever necessary. To put it simply, the sensor inputs send information to the ECU which evaluates this information and sends information to the actuator outputs accordingly. The oxygen sensor being at the end of the cycle is able to send feedback to the ECU, this will then enable the ECU to make adjustments and after the cycle is repeated, see the outcome of the adjustments and if any further adjustments are necessary to maintain the air fuel ratio and maximum fuel efficiency. This circuit is continuously working and operating as the engine is.

In this report, I have explained the function of the sensor inputs and actuator outputs of a Toyota petrol engine. Also I have explained how this system relates to a closed loop circuit and why