Air Flow Meter – Hot Wire

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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.

Figure 6.4.1

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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.

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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.

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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 )

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Reference waveform

Figure 6.3.4

Example waveform

Figure 6.3.5 Idling 850

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Operation Steps

1. Open the software, select “Vehicle->Diagnosis->Setup”, as illustrated in Figure 6.3.2.

Figure 6.3.2

2. Click “Sensors->Throttle Position -> Throttle Position Switch”, and click “OK”, as illustrated in Figure 6.3.3.

Figure 6.3.3

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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.

Figure 6.3.1

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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.

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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.

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Camshaft Sensor

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'.