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Title: Air Flow Meter – Hot Wire [Print this page]
Author: WisdomAugust Time: 2019-2-16 12:59
Title: Air Flow Meter – Hot Wire
Air Flow Meter – Hot Wire
An air flow meter is used in some automobiles to measure the quantity of air going into the internal combustion engine.
All modern electronically controlled diesel engines use air flow meter, as it is the only possible means of determining the
air intake for them. In the case of a petrol engine, the electronic control unit (ECU) then calculates how much fuel is
needed to inject into the cylinder ports. In the diesel engine, the ECU meters the fuel through the injectors into the
engines cylinders during the compression stroke.
The AFM is once again located between the air filter and the throttle butterfly. Inside the component are two wires, one
of which is used to convey the temperature of the incoming air and the other heated to a high temperature (approximately
120℃) by passing a small current through it. As the air flows across the heated wire, it has a cooling effect on it causing
a temperature change; a small circuit inside the component increases the current passing through the wire to maintain
the temperature, and it is the recognition of this current that signals to the ECM the mass air flow.
Author: WisdomAugust Time: 2019-2-18 08:28
Connect the oscilloscope
1. Plug a BNC test lead(HT30A) into channel 1 on the DSO3064(A).
2. Fit a large black gator clip on the black (negative) plug on the test lead and an acupuncture probe(HT307)
or multimeter probe on the coloured (positive) plug.
3. Place the black gator clip to the battery negative terminal and probe the air flow sensor's output terminal with
the acupuncture or multimeter probe as illustrated in Figure 6.1.1. If you cannot reach the terminal or plug with a
probe, then you may be able to use a breakout box or lead if you have one available.
[attach]2620[/attach]
Figure 6.1.1
Author: WisdomAugust Time: 2019-2-19 08:23
Operation Steps:
1. Open the software, select “Vehicle->Diagnosis->Setup”, as illustrated in Figure 6.1.2.
[attach]2621[/attach]
Figure 6.1.2
Author: WisdomAugust Time: 2019-2-20 08:20
[attach]2630[/attach]
Figure 6.1.3
Author: WisdomAugust Time: 2019-2-21 13:08
Reference waveform
[attach]2634[/attach]
Figure 6.1.4
Author: WisdomAugust Time: 2019-2-22 08:18
Example waveform
[attach]2635[/attach]
Figure 6.1.5
Author: WisdomAugust Time: 2019-2-25 08:09
Notes:
The voltage output from the Air Flow Meter (AFM) should be proportional to airflow.
This can be measured on an oscilloscope and should look similar to the example
shown. The waveform should show approximately 1.0 volt when the engine is at
idle, but this voltage will rise as the engine is accelerated and air volume is increased,
producing an initial peak. This peak is due to the initial influx of air and drops momentarily
before the voltage rises again to another peak of about 4.0 to 4.5 volts. This voltage
will, however, depend on how hard the engine is accelerated, and a lower voltage is not
necessarily a fault within the AFM.
On deceleration the voltage drops sharply as the throttle butterfly closes, reducing the
airflow, and the engine returns to idle. The final voltage drops gradually on an engine
fitted with an idle speed control valve, as this slowly returns the engine to base idle as
an anti-stall characteristic.
Author: WisdomAugust Time: 2019-3-1 08:47
Camshaft Sensor
[attach]2648[/attach]
Figure 6.2.5 Idling 1500
Notes:
The camshaft sensor is sometimes referred to as the Cylinder Identification Sensor(CIS) and is used as a reference to
time the sequential fuel injection. The signal waveform can be either a permanent magnetic sine wave or in this case a
digital square wave.
The Electronic Control Unit (ECU) needs to see the signal when the engine is started for its reference; if this is absent,
it can put the ECU into 'limp-home'.
Author: WisdomAugust Time: 2019-3-2 08:13
Throttle Position - Switch
The throttle position sensor is sometimes referred to as the throttle switch. It measures and reports the
amount of throttle opening to the Engine Control Module (ECM). The ECM uses this information to make
adjustments to the mixture of fuel and air used for combustion. As the throttle is opened, the engine requires
more fuel in the mixture to provide needed power.
The throttle switch is a 3 wire twin contact device that is operated by the throttle butterfly spindle. This
will provide information to the Electronic Control Module (ECM) for throttle closed, throttle open and
wide open throttle position (90% open). When the engine is at tick over the idle contacts are closed,
as the throttle is opened these contacts open, sending a signal to the ECM to indicate cruise/part load
condition. At the 90% wide open throttle position the other contacts are closed and the signal is sent to
the ECM to provide extra fuel enrichment for acceleration.
Author: WisdomAugust Time: 2019-3-4 08:12
Connect the oscilloscope
1. Plug a BNC test lead(HT30A) into channel 1 on the DSO3064(A), place a large black gator clip (HT18A)
on the test lead with the black moulding (negative) and an acupuncture(HT307) or multimeter probe onto the
test lead with the red moulding (positive). Place the black gator clip onto the battery negative terminal and probe
the throttle switch with the acupuncture or multimeter probe.
2. Plug a BNC test lead into channel 2 on the DSO3064(A) and an acupuncture or multimeter probe onto the test
lead with the red moulding (positive). Probe the throttle pedal switch with the other acupuncture or multimeter as
illustrated in Figure 6.3.1.
Author: WisdomAugust Time: 2019-3-5 08:25
Note: the switch will have three wires normally consisting of:
(i) idle circuit contacts
(ii) full load circuit contacts
(iii) earth
Check the technical data for the system to be tested.
[attach]2669[/attach]
Figure 6.3.1
Author: WisdomAugust Time: 2019-3-6 08:49
Operation Steps
1. Open the software, select “Vehicle->Diagnosis->Setup”, as illustrated in Figure 6.3.2.
[attach]2670[/attach]
Figure 6.3.2
2. Click “Sensors->Throttle Position -> Throttle Position Switch”, and click “OK”, as illustrated in Figure 6.3.3.
[attach]2671[/attach]
Figure 6.3.3
Author: WisdomAugust Time: 2019-3-7 08:14
Reference waveform
[attach]2672[/attach]
Figure 6.3.4
Example waveform
[attach]2673[/attach]
Figure 6.3.5 Idling 850
Author: WisdomAugust Time: 2019-3-8 09:24
Notes:
The Throttle Switch (TS) is invariable a three wire device operating at 5 volts (12 volts on very early systems).
The objective of the throttle switch is to inform the Electronic Control Module (ECM) of the position of the throttle
movement at throttle housing.
The example waveform shows a dual trace picture, monitoring the two switched terminals of the TS. The throttle
has been operated from rest to full throttle and back to rest. The yellow trace is the idle contact circuit, once the
throttle starts operating this switch opens and its voltage changes from 0 to 5 volts. It will remain at 5 volts, even
at full throttle, until the throttle is back at its idle position.
The blue trace is the full load circuit and is at 5 volts (in its open position) until full throttle is achieved. As the operator
only stayed in the full throttle position for a very short period (560 ms) the switch soon opens again and the voltage
changes back from 0 to 5.
This device can be switched in several ways, so it will be necessary to check with the vehicle and module specific data.
Inside the switch there are two sets of contacts, this enables three stages of throttle movement to be monitored.
These are:
u Throttle closed
u Throttle part open
u Throttle fully open (sometimes referred to as wide open throttle - WOT )
Author: WisdomAugust Time: 2019-3-11 08:30
Injectors – Single Point (Voltage)
Single Point Injector (SPI) is also sometimes referred to as Throttle Body Injection (TBI).
A single injector is used (on larger engines two injectors can be used) in what may have the outward
appearance to be a carburettor housing.
The resultant waveform from the SPI system will show an initial injection period followed by multi-pulsing
of the injector in the remainder of the trace. This section of the waveform is called the supplementary
duration and is the only part of the injection trace to expand.
Author: WisdomAugust Time: 2019-3-12 08:12
Connect the oscilloscope
1. Plug the 20:1 Attenuator into channel 1 on the DSO3064(A) and the BNC test lead (HT30A) into the
other end of the attenuator. Place a large black gator clip(HT18A) on the test lead with the black moulding
(negative) and an acupuncture(HT307) or multimeter probe onto the test lead with the red moulding (positive).
2. Attach the black gator clip onto the battery negative terminal and probe the switched earth side of the
injector with the acupuncture or multimeter probe as illustrated in figure 6.4.1.
Author: WisdomAugust Time: 2019-3-13 11:39
With the example waveform displayed on the screen you can now hit the space bar to start looking at
live readings. Snap the accelerator quickly from idle to full throttle and observe the supplementary injection
of the waveform expanding under acceleration.
[attach]2682[/attach]
Figure 6.4.1
Author: WisdomAugust Time: 2019-3-14 09:10
Operation Steps:
1. Open the software, select “Vehicle->Diagnosis->Setup”, as illustrated in Figure 6.1.2.
2. Click “Sensors->Injector Diagnonis -> Single-point Injector(Voltage)”, and click “OK”, as illustrated in Figure 6.1.3.
[attach]2683[/attach]
Figure 6.4.2
[attach]2684[/attach]
Figure 6.4.3
Author: WisdomAugust Time: 2019-3-15 08:08
Reference Waveform
[attach]2686[/attach]
Figure 6.4.4
Author: WisdomAugust Time: 2019-3-16 08:13
Example Waveform
[attach]2689[/attach]
Figure 6.4.5
Notes:
Neither wire of the injector should be connected to the negative (ground) input of the oscilloscope as this could
cause a short circuit.
The 20:1 Attenuator is used to monitor the induced voltage that is created when the earth path to the injector is
removed. This voltage will be in the region of 60 to 80 volts.
Author: WisdomAugust Time: 2020-2-10 08:01
Secondary-Distributorless (Positive Fired)
Technical information
Ignition coil is also referred to as a spark coil and used to transform lower voltages of power to the higher
voltages of power required to fire a system's spark plugs. It is similar to an electric transformer, consists of
primary and secondary winding circuits. Inside the coil's primary winding is the secondary winding. This is
coiled around a multi-laminated iron core and has approximately 20,000 to 30,000 turns. One end is connected
to the primary terminal and the other to the coil tower.
The ignition probe(HT25) voltage is produced by mutual induction between the primary winding and the secondary
winding, with the central soft iron core intensifying the magnetic field between them.
Author: WisdomAugust Time: 2020-2-11 07:37
The voltage measured at the spark plug is the voltage required to jump the plug gap in varying conditions.
This voltage is determined by the spark plug gap, rotor air gap, etc.
The plug kilovolt (kV) requirement of older engines tends to be lower than that of the modern engine, as the
later designs run higher compression ratios, leaner air/fuel ratios, and larger spark plug gaps.
Author: WisdomAugust Time: 2020-2-12 07:59
The modern engine with Distributorless Ignition System (DIS) has all the advantages of a constant energy
electronic ignition system, but with the added bonus of the distributor cap, king lead and rotor arm being
removed from the system. Reliability problems from dampness and tracking are now almost eliminated.
DIS has its own drawbacks by having half of the plugs firing with an acceptable negative voltage, while the
other half are fired by the less acceptable positive polarity. This has the effect of increased plug wear on the
positive fired plugs.
Author: WisdomAugust Time: 2020-2-13 07:30
Connect the oscilloscope
1. Plug an auto-ignition probe (HT25) into channel 1 on the DSO3064(A).
2. Clip the lead's crocodile clip on suitable earth.
3. Fit the HT clip on one of the engine's positively-fired plug leads.
If the live waveform is missing or upside-down, you have selected a negatively fired plug. Either choose a
different plug lead or load the secondary negative waveform from the drop-down menu.
Author: WisdomAugust Time: 2020-2-14 07:40
Warning: When attaching or removing secondary ignition pickups from damaged HT25 leads there is
a risk of electric shock. To eliminate this danger, attach and remove the secondary ignition pickup with
the ignition turned off.
[attach]3401[/attach]
Author: WisdomAugust Time: 2020-2-15 07:42
Follow these steps:
1. Click “Vehicle->Diagnosis”, as illustrated in Figure 6.5.2
2. Click “Ignition->Secondary-> Secondary DIS(Positive-fired)”,click “OK” , as illustrated in Figure 6.5.3.
[attach]3408[/attach]
Figure 6.5.2
[attach]3409[/attach]
Figure 6.5.3
Author: WisdomAugust Time: 2020-2-17 07:41
Reference waveform
[attach]3410[/attach]
Figure 6.5.4
Example Waveform
[attach]3411[/attach]
Figure 6.5.5
Notes:
When the positive fired plug kV's are recorded on distributor Ignition Systems (DIS), the voltage should be
as shown and not inverted, as this would suggest that the wrong lead has been chosen.
While the engine is running, the plug voltage continuously fluctuates and the display moves up and down.
Author: WisdomAugust Time: 2020-2-18 07:53
Lambda Sensor - Zirconia
The lambda sensor is also referred to as the Oxygen O2 sensor or a Heated Exhaust Gas Oxygen
(HEGO) sensor and plays a very important role in the control of exhaust emissions on a catalytic
equipped vehicle. The lambda sensor is fitted into the exhaust pipe before the catalytic converter;
cars using the new EOBD2 will also have a post cat lambda sensor.
The sensor will have varying electrical connections and may have up to four wires; it reacts to the oxygen
content in the exhaust system and will produce a small voltage depending on the Air/Fuel mixture seen at
the time. The voltage range seen will, in most cases, vary between 0.2 and 0.8 volts: 0.2 volts indicates a
lean mixture and a voltage of 0.8v shows a richer mixture. A vehicle equipped with a lambda sensor is said
to have 'closed-loop', this means that after the fuel has been burnt during the combustion process, the sensor
will analyze the resultant emissions and readjust the engine's fuelling accordingly. Lambda sensors can have
a heater element which heats the sensor to its optimum operating temperature of 600℃, this enables the sensor
to be located further away from the heat source at the manifold to a 'cleaner' location.
Author: WisdomAugust Time: 2020-2-19 13:42
The lambda sensor is essentially two porous platinum electrodes. The outer electrode surface is exposed
to the exhaust gasses and is coated in a porous ceramic with the inner coated surface exposed to fresh air.
The most commonly used sensor uses a Zirconia element, producing a voltage when a difference in oxygen
content is seen between the two electrodes. This signal is then sent to the Electronic Control Module (ECM)
and the mixture is adjusted accordingly. Titania is also used in the manufacture of another type of lambda
sensor that offers a faster switching time than the more common Zirconia sensor.
Author: WisdomAugust Time: 2020-2-20 07:32
The titania oxygen sensor differs from the zirconia sensor in the fact that it is incapable of producing its
own output voltage and is therefore reliant upon a 5 volt supply from the vehicle's ECU. The reference
voltage is altered according to the engine's air-fuel ratio, with a lean mixture returning a voltage as low
as 0.4 volts to a rich mixture producing a voltage in the region of 4.0 volts.
A constant high voltage output from the zirconia shows that the engine is running constantly rich and is
outside the ECU's adjusting range, whereas a low voltage indicates a lean or weak mixture.
Author: WisdomAugust Time: 2020-2-21 07:40
Electrical Connections (zirconia type only)
Single wire: this wire is the self-generated voltage output from the sensor and is generally black in color.
Two wires: this will have an output wire and an output earth return.
Three wires: this will have a single output wire and two wires for the heater element (supply and earth).
The internal heating element raises the temperature to ensure faster control when starting from cold.
Four wires: this unit has a signal and signals earth return wires. The additional two wires are for the heater
element.
Author: WisdomAugust Time: 2020-2-24 08:33
Connect the oscilloscope
1. Plug a BNC test lead (HT30A) into channel 1 on the DSO3064(A).
2. Fit a large black gator clip on the black (negative) plug on the test lead and an acupuncture probe
(HT307) or multimeter probe on the colored (positive) plug.
3. Place the black gator clip to the battery negative terminal and probe the lambda sensors output
connection with the acupuncture or multimeter probe as illustrated in Figure 6.6.1.
Regardless of the number of wires connecting the lambda sensor to the vehicle's ECU, the output
from the sensor will invariably be on the black wire.
[attach]3418[/attach]
Figure 6.6.1
Author: WisdomAugust Time: 2020-2-25 09:15
Operation Steps:
1. Open the software, select “Vehicle->Diagnosis Setup”, as illustrated in Figure 6.6.2.
[attach]3419[/attach]
Figure 6.6.2
2. Click “Sensors-> Lambda Sensors -> Lambda Sensor Zirconia”, and click “OK”, as illustrated in Figure 6.6.3.
[attach]3420[/attach]
Figure 6.6.3
Author: WisdomAugust Time: 2020-3-2 09:55
Reference Waveform
[attach]3421[/attach]
Example waveform
[attach]3422[/attach]
Figure 6.6.5
Author: WisdomAugust Time: 2020-3-3 08:25
Note
The sensor will have varying electrical connections and may have up to four wires; it reacts to the oxygen
content in the exhaust system and will produce a small voltage depending on the Air/Fuel mixture seen at
the time. The voltage range seen will, in most cases, vary between 0.2 and 0.8 volts: 0.2 volts indicates a
lean mixture and a voltage of 0.8v shows a richer mixture.
A vehicle equipped with a lambda sensor is said to have 'closed loop', this means that after the fuel has been
burnt during the combustion process, the sensor will analyze the emissions and re-adjust the engine's fuelling
accordingly.
Lambda sensors can have a heater element to assist the sensor reaching its optimum operating temperature.
Zirconia sensors when working correctly will switch approximately once per second (1 Hz) and will only start
to switch when at normal operating temperature. This switching can be seen on the oscilloscope, and the
waveform should look similar to the one in the example waveform. If the frequency of the switching is slower
than anticipated, remove the sensor and clean with a solvent spray and this may improve the response time.
The sensor is inoperative below 300℃.
Author: WisdomAugust Time: 2020-3-4 08:07
Primary Ignition
Connect the Oscilloscope
1. Plug the 20:1 Attenuator (HT201) into channel 1 on the oscilloscope and plug a BNC test lead
(HT30A) into the attenuator.
2. Place a large black gator clip(HT18A) on the black test plug (negative) and a small red gator
clip on the colored test plug (positive).
3. Place the black gator clip onto the battery negative terminal and probe the coil's negative terminal
with the small red crocodile clip.
Author: WisdomAugust Time: 2020-3-5 08:07
Operation Steps:
1. Open the software, select “Vehicle->Diagnosis->Setup”, as illustrated in Figure 7.1.2.
2. Click “Ignition->Primary-> Primary Ignition (Voltage)”, and click “OK”, as illustrated in Figure 7.1.3.
3. Click “OK”.
[attach]3431[/attach]
Figure 7.1.2
[attach]3432[/attach]
Figure 7.1.3
Author: WisdomAugust Time: 2020-3-6 08:14
Reference waveform
[attach]3433[/attach]
Figure 7.1.4
Example Waveform
[attach]3434[/attach]
Author: WisdomAugust Time: 2020-3-9 08:12
Technical information
The primary ignition is so called as it forms the first part of the ignition circuit. Through the ignition coil,
it drives the secondary High Tension (HT) output. The primary circuit has evolved from the basic contact
breaker points and condenser to the distributorless and coil-per-cylinder systems in common use today.
All of these ignition systems rely on the magnetic induction principle.
Magnetic Induction
This principle starts with a magnetic field being produced, as the coil's earth circuit is completed by either
the contacts or the amplifier providing the coil negative terminal with a path to earth. When this circuit is
complete, a magnetic field is produced and builds until the coil becomes magnetically saturated. At the
predetermined point of ignition, the coil's earth is removed and the magnetic field collapses. As the field
inside the coil's 250 to 350 primary windings collapses, it induces a voltage of 150 to 350 volts.
The induced voltage is determined by:
· The number of turns in the primary winding
· The strength of the magnetic flux, which is proportional to the current in the primary circuit
· The rate of collapse, which is determined by the speed of switching of the earth path
Author: WisdomAugust Time: 2020-3-10 08:05
Dwell period
Dwell is measured as an angle: with contact ignition, this is determined by the points gap. The definition
of contact ignition dwell is: 'the number of degrees of distributor rotation with the contacts closed'.
As an example, a 4 cylinder engine has a dwell of approximately 45 degrees, which is 50% of one
cylinder's complete primary cycle. The dwell period on an engine with electronic ignition is controlled
by the current-limiting circuit within the amplifier or Electronic Control Module (ECM).
The dwell angle on a constant-energy system expands as the engine speed increases, to compensate
for a shorter period of rotation and maximise the strength of the magnetic field. The term 'constant energy'
refers to the available voltage produced by the coil. This remains constant regardless of engine speed,
unlike contact ignition where an increase in engine speed means the contacts are closed for a shorter time
and gives the coil less time to saturate.
The induced voltage on a variable dwell system remains constant regardless of engine speed, while it
reduces on contact systems. This induced voltage can be seen on a primary waveform.
Author: WisdomAugust Time: 2020-3-11 08:18
Secondary-Distributorless (Positive Fired)
Technical information
Ignition coil is also referred to as a spark coil and used to transform lower voltages of power to the higher
voltages of power required to fire a system's spark plugs. It is similar to an electric transformer, consists
of primary and secondary winding circuits. Inside the coil's primary winding is the secondary winding.
This is coiled around a multi-laminated iron core and has approximately 20,000 to 30,000 turns.
One end is connected to the primary terminal and the other to the coil tower.
Author: WisdomAugust Time: 2020-3-12 08:45
The ignition probe(HT25) voltage is produced by mutual induction between the primary winding and the
secondary winding, with the central soft iron core intensifying the magnetic field between them.
The voltage measured at the spark plug is the voltage required to jump the plug gap in varying conditions.
This voltage is determined by a spark plug gap, rotor air gap etc.
The plug kilovolt (kV) requirement of older engines tends to be lower than that of the modern engine, as
the later designs run higher compression ratios, leaner air/fuel ratios, and larger spark plug gaps.
Author: WisdomAugust Time: 2020-3-13 08:07
The modern engine with Distributorless Ignition System (DIS) has all the advantages of a constant energy
electronic ignition system, but with the added bonus of the distributor cap, king lead and rotor arm being
removed from the system. Reliability problems from dampness and tracking are now almost eliminated.
DIS has its own drawbacks by having half of the plugs firing with an acceptable negative voltage, while
the other half are fired by the less acceptable positive polarity. This has the effect of increased plug wear
on the positive fired plugs.
Author: WisdomAugust Time: 2020-3-14 08:21
Connect the oscilloscope
1. Plug an auto-ignition probe (HT25) into channel 1 on the oscilloscope.
2. Clip the lead's crocodile clip on suitable earth.
3. Plug the Coil-on extension lead(HT308) into the engine's positively-fired plug of an air cylinder.
4. Fit the HT25 clip on the Coil-on extension lead as illustrated in Figure 6.5.1.
[attach]3443[/attach]
Figure 6.5.1
Author: WisdomAugust Time: 2020-3-16 08:52
Follow these steps:
1. Click “Vehicle->Diagnosis”, as illustrated in Figure 6.5.2
2. Click “Ignition->Secondary-> Secondary DIS (Positive-fired)”, click “OK”, as illustrated in Figure 6.5.3.
[attach]3445[/attach]
Figure 6.5.2
[attach]3446[/attach]
Figure 6.5.3
Author: WisdomAugust Time: 2020-4-1 09:25
Reference waveform
[attach]3456[/attach]
Example Waveform
[attach]3457[/attach]
Figure 6.5.5
Notes:
When the positive fired plug kV's are recorded on distributor less Ignition Systems (DIS), the voltage should
be as shown and not inverted, as this would suggest that the wrong lead has been chosen.
While the engine is running, the plug voltage continuously fluctuates and the display moves up and down.
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