1. Listen to the injectors as the engine idling. Use stethoscope, vacuum line or long screwdriver.
Sound like a sharp tap? Yes
Can you get to all the injectors? Yes
2. Check voltage to the injectors when idling or Key on. This makes sure you have battery voltage to the injectors so they can work.
Battery voltage: 14.23V
Voltage at each injector
Cyl#2: 14.13V
Cyl#4: 14.13V
Cyl#6: 14.13V
3. With engine idling, watch injector firing by using an LED tester or test light.
Testing with Toyota 4A-FE
4. With engine idling, watch injector firing by using a multimeter set to read %(duly cycle).
Cyl#1: 5.0%
Cyl#2: 5.0%
Cyl#3: 5.0%
Cyl#4: 5.0%
5. With the multimeter still set to read %(duly cycle), accelerate the engine with short, fast throttle openings and note maximum % reading you can get on the multimeter.
Cyl#1: 15.5%
Cyl#2: 15.5%
Cyl#3: 15.5%
Cyl#4: 15.5%
6. Set the multimeter to read Hz, and with the engine idling, record the readings for each cylinder in the boxes below:
Cyl#2: 32Hz
Cyl#4: 32Hz
Cyl#6: 32Hz
Formula to calculate the pulse width of each injector Pulse width ms = (duty cylce / 100) / Frequency kHz
Cyl#1: (5.0 / 100) / 0.032 = 1.56ms
Primary & Secondary Ignition Patterns
Make: Toyota
Model: 4A-FE
1. Labscaope setting
Coil wire on top of the distributor cap
number 1 spark plug connection
negative side of the ignition coil
2. Primary Voltage Patterns
Cyl 1
Cyl 2
Cyl 3
Cyl 4
Firing Voltage(A)
over 300V
over 300V
over 300V
over 300V
Burn Voltage(B)
50V
50V
50V
50V
Dwell Time(C)
6.7ms
6.7ms
6.7ms
6.7ms
Burn Time(D)
1.3ms
1.3ms
1.3ms
1.3ms
The cylinders are displayed from left to right by firing order. By having a parade display, the signals can be compared with one another.
Raster is the best scope position to view the spark lines of all the cylinders to check for differences.(spark line length and transistor-on point) Cylinder #1 appears at the bottom of the screen and all other cylinder patterns are displayed upward in the engine's firing order.
Burn time is usually more reliable than KV firing voltage so it can be used for diagnosis.
3. Secondary Voltage Patterns
Cyl 1
Cyl 2
Cyl 3
Cyl 4
Firing Voltage
5.0kV
4.0kV
5.0kV
5.0kV
Burn Time
1.4ms
1.3ms
1.4ms
1.5ms
Snap Acceleration
12kV
12kV
12kV
12kV
The height of the firing voltage should be between 5kV and 15 kV with not more than a 3kV difference between highest and the lowest cylinder's firing voltage.
Following are guidelines for spark line lenght(Burn time):
0.8 ms : too short
1.5 ms : average
2.2 ms : too long
Disconnect one spark plug wire(Cyl #3) and short to the engine with a jumper wire. Start the engine and let it idle.
Cyl 1
Cyl 2
Cyl 3
Cyl 4
Firing Voltage
5.0kV
5.0kV
3.0kV
5.0kV
Burn Time
1.4ms
1.3ms
1.9ms
1.5ms
This spark plug has a long burn time comparing with other cylinders due to a grounded plug wire. Less energy is used to fire the spark plug, the burn time was longer.
There is no a spark tester. So we could not do some experiments. Instead some theories are put here.
If the spark line is too short, possible causes include the following:
1. Spark plugs gapped too widely
2. Worn cap or rotor
3. High-resistance spark plug wire
4. Air-fuel mixture too lean
If the spark line is too long, possible causes include the following:
Discuss why would we bother checking the voltage supply to the fuel injectors.
The fuel injector contains an armature and a spring-loaded needle valve. When a certain voltage is applied to the solenoid coil, the armature is pulled in or pulled off. If there is no the supply voltage, the armature will not work. Therefore, the injector won't spray fuel.
If we find lower voltage at the injectors than at the battery, what can that mean? And how would injector operation be affected?
It could be faulty EFI relay, a bad wiring harness or faulty connections at the side of negative.
Negative trigger
TPS sensor
1: 4.995V
2: 0.001V
3: 0.611V
What is the purpose of the reference voltage to the throttle postion sensor?
If it does not receive reference voltage from ECU, the TPS can not deliver the proper signal.
In other words, if there is no fixed resistor between supply line and ground, a movable contact can not get a voltage relating to the resistance of the potentiometer.
What could cause problems so that there is not the correct reference voltage at the throttle position sensor?
loose connector
If there is a bad ground voltage reading(e.g above 0.5V), the TPS does not work properly.
Open the throttle to about the half open position. (2.298V)
Open the throttle to the full open postion (3.881V)
Describe how a TPS sensor works.
Throttle postion sensors are the potentiometer type sensors. The ECU uses their input to determine the amount of the throttle opening . Typical potentiometer is a variable resistance sensor with three terminals. One end of the resistor receives a reference voltage(5V), while the other end is grounded. The third terminal is attached to a movable contact that slides across the resistor to vary its resistance. The movable contact is connected to the throttle butterfly.
Discuss what type of sensor voltages should go to the ECU as the throttle is opened and closed.
When the throttle is opened, the sensor voltage increases. When the throttle is closed, the sensor voltage decreases.
WOT(Wide Open Throttle)- approximately 4.5V
Closed Throttle - approximately 0.5V
Describe problems which could occur to prevent the TPS from sending the correct voltage to ECU.
Due to overheating, inside of the TPS can be shorted or wiring harness shorted.
Loose connection or dirty connections also can be a problem to send correct voltage to ECU.
When there is a problem with a movable contact, it can cause a problem.
Draw a full circuit diagram for the TPS on this vehicle.
ECT(Engine Coolant Temperature) Sensor
Make: Lexus
Model: ES300
Ignition "On", No starting
Measurement voltage: 1.192V
Ignition: On, Engine starting and after two minutes
Measurment Voltage: 0.711V
Good gound voltage testing
Measurment voltage: 0.037V
As shown above measurement, a warmer engine shows a lower voltage.
Describe how an ECT sensor works.
As shown below a circuit diagram, two resistors are connected in series. Therefore, when the water temperature is cold, the resistance of the second resistor is larger and more voltage is needed to push the electrons across the second resistor. When the water temperature is warm or hot, the resistance of the second resistor is smaller and less voltage is need to push the electrons across the second resistor.
Draw the circuit diagram for the ECT sensor for this vehicle. Include some detail inside the ECU.
Describe how the ECT sensor voltage affects the fuel injection output from the ECU.
When the engine is cold(sending 1.xx volts to ECU), the fuel mixture must be richer to prevent stalling and engine stumble. When the engine is warm(sending 0.xx volts to ECU), the fuel mixture can be leaner to provide maximum fuel economy and lower exhaust emissions.
Describe what could go wrong to creat an incorrect voltage for the ECU.
If the ECT has a poor wiring connection(high resistance), the ECU will supply a richer-than-normal fuel mixture based on the resistance of the ECT. Poor fuel economy can be caused by a defective sensor or high resistance in the sensor wiring. If the ECT was shorted and has too low resistance, the ECU will supply a leaner-than-normal fuel mixture. A too lean fuel mixture can cause driveability problems.
Why is it important to measure the ECU earth?
If there is a bad ground voltage reading, it affects the ECT signal sending to ECU and it affects the engine operation. (In here, the bad ground voltage is above 0.5V)
Discuss what could go wrong so that the ECU earth or gournd is not good.
If affects the reference voltage so the ECT would not send an incorrect signal to ECU.
MAP Sensor
Ignition "ON", no engine starting : 1.812V
Starting engine and idle: 0.458V(?)
Short acceleration: 1.1V(?)
Describe how MAP sensor works to tell the engine how much air comes into the engine.
The typical MAP sensor consists of a silicon wafer sealed on one side with a perfect vacuum and the other side is exposed to an intake manifold vacuum. There are four resistors attached to the silicon wafer which changes in resistance, when strain is applied to the wafer. The resistors are electrically connected to a wheatstone bridge circuit and then to a differential amplifer, which creates a voltage in proportion to the vacuum applied. At idle, a high vacuum is produced.(low pressure and less air coming in). So it produces a low voltage. When the engine starting to accelerate and the throttle is opened, the pressure inside the manifold rises(low vacuum and more air coming in). So it produces a high voltage.
What could go wrong so the ECU did not receive the correct signal from the MAP sensor?
If there is air leak around the hose, it can cause driveability problems(stalling, hesitation) and poor fuel economy. Also there can be other causes such as loose connection, defective silicon chip.
Draw the circuit diagram for the MAP sensor on this engine.
MAF Sensor
<MAF>
<IAT>
The mass air flow sensor measures the amount of air flowing through the throttle valve. There is a heated platinum wire which is exposed to the flow of the intake air. By applying a specific electrical current to the wire, the ECU heats it to a given temperature. The flow of incoming air cools both the wire and the internal thermistor. The voltage is proportional to the air flow through the sensor.
Typical idle sensor voltage is 1V.
The ignition system includes the components as shown below -
Battery/Alternator
Ignition switch
Ballast resistor
Coils(Primary winding/Secondary winding)
Igniter(Ignition module)
Distributor
HT leads
Spark plugs
When the battery voltage is applied, the ignition switch is on and the negative side is grounded, the current flows through primary winding of the coil and magnetic field established. When the negative side is ground off, the magnetic field collapsed and induce a high voltage into secondary winding of the coil. Then the distributor sends the high voltage to each spark plug at the correct time. A high voltage arc occurs across the gap of the spark plug inside the combustion chamber.
The primary winding has 150 turns of heavy wire and the secondary winding has 20,000 turns of fine wire. The secondary winding has about 100 times the number of turns of the primary winding.(Turns ratio 1:100)
Formular
Np: number of turns in primary winding, Ns: number of turns in secondary winding
Vp: voltage in primary winding, Vs: voltage in secondary winding
Ip: current in primary winding, Is: current in secondary winding
Example:
If Vp=30V, Np=10 and Ns=1000 then calculate Vs?
10 / 1000 = 80 / Vs
Vs = 80000 / 10 = 8000V
If Ip=6A then calculate Is?
10 /1000 = Is / 6
Is = 10/1000 x 6 = 60mA
Practical
Testing ignition coils
Coil Specifications
Coil#1 No CIT-118
Coil#1 Voltage 12V
Coil#1 Primary 1.2Ω (Test result: 1.2Ω)
Coil#1 Secondary 8.5k~9.5kΩ (Test result: 9.29kΩ)
<- Secondary winding testing
<- Primary winding testing
Earth leakage testing; 0L
Coil#2 No Bosch SU12R Coil#2 Voltage 12V Coil#2 Primary 1.5Ω (Test result: 1.5Ω) Coil#2 15kΩ (Test result: 14.76kΩ)
<- Primary winding testing
<- Secondary winding testing
Earth Leakage testing: 0L
Wasted Spark Coil Pack
Coil#1 Secondary 7.24kΩ
Coil#2 Secondary 7.05kΩ
pin#1 - pin#2 : 1.2Ω
pin#3 - pin#4 : 0.1Ω
pin#2 - pin#4 : 0.6Ω
pin#1 - pin#4 : 0.6Ω
How can we recognise which one is which?
1. Measure the resistance between each two pins.
pin#1-pin#2 : 1.2Ω
pin#2-pin#3 : 0.6Ω
pin#3-pin#4 : 0.2Ω
pin#1-pin#3 : 0.6Ω
pin#1-pin#4 : 0.6Ω
As shown above measurments, we can see that there are two coils and they are connected.
Current draw: 6.02A
Coil calculated Voltage drop 10.59V
Coil measured Voltage drop 10.19V
Ballast resistor calculated voltage drop 1.41V
Ballast resistor measured voltage drop 0.04V
Wiring up ignition systems
1. Wire up an ignition module using a function generator to trigger the module
2. Wire up an ignition module using a distributor to trigger the module
3. Wire up the wasted spark ignition system using the function generator to trigger the module
Waste-spark system uses one ignition coil to fire the spark plugs for two cylinders at the same time.
Waste-spark ignition is another name for the distributorless ignition system or electronic ignition. A 4-cylinder engine uses two ignition coils and a 6-cylinder engine uses three ignition coils.
Both spark plugs fire at the same time. When one cylinder is on the compression stroke, the other cylinder is on the exhaust stroke. The spark that occurs on the exhaust stroke is called the waste spark, because it does no useful work and is only used as a ground path for the secondary winding of the ignition coil. The cylinder on the compression stroke uses the remaining coil energy.
4. Wire up the coil over ignition system using the function generator to trigger the module
#1 - Battery, #2 - Earth, #3 - Trigger
Coil-on-plug system uses a single ignition coil for each cylinder with the coil placed above or near the spark plug. The advantage of the Coil-on-plug systems is that it doesn't need the spark plug wires thatoften cause electronagnetic interference.
5. Build the ignition circuit on a breadboard using two 2N2222 transistors
Ic = 800mA
First experiment
Measure the resistance of the ballast resistor and primary winding of the coil.
Resistance of the ballast resistor: 2Ω
Resistance of the primary winding of the coil: 3.2Ω
To calculate Rc, firstly refer to the datasheet of the transistor which is TIP31C. According to the datasheet, maximum Ic is 3A. For the safety factor, divide the maximum current by two. RT=12 / 1.5
RT=8 Rc=8-(2+3.2) Therefore Rc = 2.8Ω
Rb=(5-0.7) / 1.5 = 2.9Ω
Second experiment
Measure the resistance of the ballast resistor and primary winding of the coil.
Resistance of the ballast resistor: 2Ω
Resistance of the primary winding of the coil: 3.2Ω
To calculate Rc, firstly refer to the datasheet of the transistor which is TIP31C. According to the datasheet, maximum Ic is 3A. For the safety factor, divide the maximum current by two. RT=(12-0.7-0.05) / 1.5
RT=7.5 Rc=7.5-(2+3.2) Therefore Rc = 2.3Ω
Rb=(5-0.7-0.7) / 400mA = 9Ω(why Ib=400mA? - from the datasheet, the maximum current is 800mA, for the purpose of safety factor, divide the maximum current by two. Therefore I = 400mA)
