The point A shows us that the normal idling voltage of the maf is 1.198V. When the engine accelerates, the signal changes to approx 2.6V(point B). Then during the deceleration, the signal drops sharply to the normal idling voltage which is 1.198V(point C).
Explain in detail an electrical fault that would make this unit operate incorrectly.
Dirt, oil can coat the sensing wire. The contaminated sensor often overestimates the amount of air entering the engine at idle and therefore causes the fuel system to go rich. At high engine speeds, the contaminaton can cause the sensor to underestimate the amount of air entering the engine. As a result, the fuel system will go lean.
ECT sensor Volt/division: 0.5V Time/division: 5S
ECT is a negative temperature coefficient. As the coolant temperature increases, the voltage drops. As shown above graph, the voltage of ECT is 1.439V. It means that coolant is half way between cold start and a warm idle condition.
If the ECT sensor has a poor connection(high resistance) at the wiring connector, the ECU will supply a richer-than -normal fuel mixture based on the resistance of the ECT sensor. Poor fuel economy can be caused by a defective sensor or high resistance in the sensor wiring. If the ECT sensor was shorted(low resistance), a leaner-than-normal fuel mixture would be supplied to the engine. A too-lean fuel mixture can cause driveability problems.
IAT sensor
Volt/division: 0.5V
Time/division: 5S
The IAT sensor is also a negative temperature coefficient(NTC) thermistor that decreases in resistance as the temperature of the sensor increases. The above graphs shows that the voltage decreases as temperature of the sensor increases.
If the IAT sensor is defective, it may be signalling the ECU that the intake air temperature is extremely cold when in fact it is warm. In such cases the ECU will supply a mixture that is much richer than normal.
If the wiring or the IAT sensor has excessive resistance, the ECU will supply a lower than normal fuel economy, and in serious cases, black exhaust smoke from the tailpipe during acceleration.
MAP sensor
Make: Toyota
Model: 4A-FE
Volt/division: 2V
Time/division: 1S
As the engine rpm increases, the intake manifold pressure rises and the voltage increases to 3.2V(point A).
When the accelerator is released, the engine vacuum rises and changes the MAP sensor voltage to 1.590V(point B).
Some dirt on the earth terminal can cause incorrect operation.
A defective vacuum hose to a MAP sensor can cause a variety of driveability problems including poor fuel economy, hesitation, stalling and rough idle.
Oxygen sensor
Make: Daihatsu
Model: YRV
Volt/division: 0.5V
Time/division: 1S
As shown patterns, approx 0.2V indicates a lean mixture and approx 0.8V indicates a rich mixture. It is important to check the cycle reaction time. Most lamda sensors will go from rich to lean in about 50 - 100ms and from lean to rich in about 75 - 150ms. If the oxygen sensor is taking slightly longer to reverse readings, this is an indication that is getting sluggish.
Normal closed loop Ziconia oxygen sensor voltage is -
Rich when high volts(Catalyic converter cleans up NOx)
Lean when low volts(Catalyic converter cleans up HC and CO)
TPS sensor
Make: Toyota
Model: 4A-FE
Volt/division: 1.0V
Time/division: 1S
Throttle position voltage is approx 0.3V(point B, throttle closed) at idle. Then as the throttle opens at 15 degrees, the throttle postion voltage reaches approx 1.0V(point A). The TP sensor voltage at idle is usually about 10% of the TP sensor voltage when the throttle is wide open, but can vary from as low as 0.3V to 1.2V, depending on the make and model of vehicle.
Any blind spots within the internal carbon track's swept area, will cause "flat spots" and "hesitations".
RPM sensor(cam or distributor)
Make: Toyota
Model: 4A-FE
Volt/division: 10V
Time/division: 20ms
This trace is an AC signal. When the trigger wheel is at the point where the air gap is the smallest, full magnetic saturation of the pickup coil has now been reached the induced voltage.(point A,peak voltage)
As the reluctor wheel pickup moves away, the air gap increases causing reluctance to magnetic field flow resulting in the magnetic lines of force collapsing across the trigger coil and inducing a voltage in the opposite direction. (point B, peak voltage)
Injectors(petrol)
Make: Toyota
Model: 4A-FE
Volt/division: 10V
Time/division: 10ms
Point A: Source voltage(Battery voltage: 14.4V) supplied to injector
Point B: Driver transistor turns on, pulling the injector pintle away from its seat, starting fuel flow
Point C: Peak voltage is caused by the collapse of the injector coil
Point D: Driver transistor turns off, ending fuel flow
Injector on-time is approx 3ms as shown above pattern.
Ignition primary
Make: Toyota
Model: 4A-FE
Volt/division: 50V
Time/division: 5ms
The ignition primary waveform measures the negative side of the ignition coil. There is no current in the coil's primary circuit until the dwell peirod(A-B). When the coil is earthed, the voltage drops to zero at point A. The induced voltage is produced by a process called magnetic inductance. At the point of ignition, the coil's earth circuit is removed and the magnetic field collapses across the coil's windings, this induces approx between 150 and 350 volts at point C(starting spark). At point D, the spark ends.
IAC(Idle air control)
Make: Toyota
Model: 4A-FE
Volt/division: 5V
Time/division: 200ms
An Idle air control controls idle speed by controlling the amount of air that passes around the throttle plate. More airflow results in a higher idle speed. The purpose of IAC systems is to stabilize idle speed during cold engine and after warm-up operations. As shown above patterns, it shows us that a duty-control rotary solenoid is used for IAC. By changing the duty ratio, a change in magnetic field causes the valve to rotate. Basically as duty ratio exceeds 50%, the valve opens the bypass passage and as duty ratio drops below 50%, the valve closes the passage.
Dual trace oscilloscope captures
MAP against Injectors(petrol)
Volt/division: A:2V / B:20V
Time/division: 50ms
Channel B shows Injector's pattern. At point A the injector is opening and the voltage is zero, because the injectors are earth triggered. When the injector is closed at point B, back EMF is produced.
Channel A shows MAP sensor's pattern. The voltage is approx 1.58V during idling.
The ECU uses the map reading to determing the fuel injector open time. The longer the injector is open, the more fuel gets into the engine.
RPM(distribution G) against Injectors(petrol)
Volt/division: A:2V / B:20V
Time/division: 50ms
Channel B shows Injector's pattern. At point A the injector is opening and the voltage is zero, because the injectors are earth triggered. When the injector is closed at point B, back EMF is produced.
Channel A shows RPM's pattern. When the trigger wheel is at the point where the air gap is the smallest, full magnetic saturation of the pickup coil has now been reached the induced voltage.(point C,peak voltage)
As the reluctor wheel pickup moves away, the air gap increases causing reluctance to magnetic field flow resulting in the magnetic lines of force collapsing across the trigger coil and inducing a voltage in the opposite direction. (point D, peak voltage)
The injector pulse is direclty related to the engine speed sensor input. As RPM increses, it needs to spray fuel faster.
Oxygen Sensor against Injectors(petrol)
Volt/division: A:20V / B:0.5V
Time/division: 1S
Ignition primary against Injectors(petrol)
Volt/division: A:2V / B:20V
Time/division: 50ms
<not good pattern>
Ignition primary voltage against Ignition primary current
(only clamp meter is provided so there is no oscilloscope pattern photo taken)
We can use five-gas exhaust analyser for emission testing and engine analysis. The five gases are HC(Hydrocarbons), CO(Carbon monoxide), CO2(Carbon dioxide), O2(Oxygen) and NOx(Oxides of nitrogen).
In the normal air condition: O2(20.9%) + N2(79%)
In ideal perfect combution: H2O + CO2 + N2 <---- O2 + N2 +HC(fuel)
Bad combution: CO, NOx, HC
The Hydrocarbons are unburned gas and are measured in ppm(parts per million). Acceptable levels of HC are 100 ppm or less. If HC is more 100 ppm, it means that there are unburned gas(excessive oil consumption). The most common cause of excessive HC emissions is a fault in the ignition system. Therefore we can check the spark plugs, spark plug wires and ignition coil.
The Carbon monoxide is unstable and easy to combine with oxygen. It is a posionous gas and should be lessthan 0.5%. High levels of CO can be caused by clogged crankcase ventilation devices such as the PCV valve, hoses and tubes.(find the cause of rich mixture)
The Carbon dioxide is produced by combining the oxygen with the carbon of the gas. Levels of CO2 should be between 12% and 15%. If the CO2 level is low, the mixture may be either too rich or too lean.
The Oxygen should be used up during the combustion process. Therefore levels of O2 should be less than 1%. High levels of O2 at idle could be due to an exhaust system leak.
The Oxides of nitrogen is a colorless, tasteless and odorless gas when it lease the engine, but as soon as it reaches the atmosphere and mixes with more oxygen, nitrogen oxides are formed. NO and NO2 are grouped together and referred to as NOx. Acceptable level of NOx should be less than 100 ppm at idle and less than 1000 ppm at WOT.
Practical
Exhaust Gas Analyser
<front>
<back>
1. With the analyser probe sensing normal air, what are the four gas readings?
CO: 0.001%
HC: 5 ppm
CO2: 0.01%
O2: 20.68%
In the normal atmosphere, there are 21% of oxygen the and 79% of the nitrogen.
2. Start the engine idling cold and record the four gas readings.
CO: 0.160%
HC: 174 ppm
CO2: 14.41%
O2: 1.16%
3. When the engine has warmed up, record the four gas readings.
4. Run the warm engine at 2500 RPM, record the four gas readings.
CO: -0.00%
HC: 785 ppm
CO2: 15.21%
O2: -0.04%
5. At idle, create a lean condition with an air leak or vacuum leak, read the four gas readings.
CO: 0.014% HC: 2276 ppm
CO2: 15.15% O2: -0.05%
If there is a vacuum leak, the O2 should be high. There is something wrong with my measurements.
6. Accelerate the engine, by blipping the throttle a few times and record the four gas readings when the CO is highest.
CO: 1.083%
HC: 1546 ppm
CO2: 14.67%
O2: 0.03%
7. Make other changes to the engine at idle, such as turning on the air conditioning or rocking the steering wheel. Record the four gas readings.
CO: 0.032%
HC: 231 ppm
CO2: 15.10%
O2: -0.04%
A catalytic converter is used to reduce exhaust emissions outside of the engine. The converter converts harmful exhaust gases into water vapor(H2O) and carbon dioxide(CO2).
The three-way catalytic converter first separates the NOx into nitrogen and oxygen and then converts the HC and CO into harmless water(H2O) and carbon dioxide(CO2). The nitrogen(N2) passes through the converter and exits the tailpipe and enters the atmosphere which is about 78% nitrogen.
1. Explain the different readings you would get from a vehicle with a catalytic converter and a vehicle without one and why?
Acceptable exhaust emissions are as follows:
Without CAT
With CAT
HC
300 ppm or less
30 to 50 ppm or less
CO
3% or less
0.3% to 0.5% or less
O2
0% to 2%
0% to 2%
CO2
12% to 15% or higher
12% to 15% or higher
NOx
Less than 100 ppm
at idle and less than 1000 ppm at WOT
Less than 100 ppm at idle and less than 1000 ppm at WOT
2. Explain what light off point means and what happens?
The catalytic converter does not work when cold, so it must be heated to its light off temperature of close to 260 degrees before it starts working at 50% effectiveness. When fully effective, the converter reaches a temperature range of 482 degrees to 871 degrees.
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:
