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ABS Speed Sensor
Air Flow Meter / Sensor
Air Intake Pressure Sensor
Alternator Current and Voltage
Amplifier Earth
Camshaft Sensor
Carbon Canister Solenoid Valve
Crankshaft sensor
Coolant Temperature sensor
Diesel Glow Plugs
Digital ECM to Ignition Amplifier Signal
Distributor Pickup
Dual Trace
Electronic Fuel Pump
Exhaust Gas Recirculation
Idle Speed Control Valve
Injectors
Knock Sensor
Lambda Sensor
MAP Sensor
Primary
Relative Compression
Secondary
Supercharger
Throttle
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Injectors - Single Point (Voltage) Diagnostics
(scroll for Single Point (Current), MultiPoint (Voltage and Current) and BoschCRD)

Single Point Injector (SPI) is also sometimes refereed 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.

Technical Information

The reason that a single point injector is used rather than a multi-point configuration is sometimes hard to justify, and can only be due to a consideration towards costing and ease of application. A single injector is used (on larger engines two injectors can be used) in what may appear to be a carburettor housing.

It has a very low operating pressure (usually around 1 bar) and the atomising of the fuel can only be described as minimal, relying on the air movement within the inlet manifold to break the fuel down into smaller particles, ready for combustion.


Due to its design the main advantage over a carburettor is that a lambda sensor can be employed ensuring that closed loop control is maintained. Multi-point will undoubtedly ensure that the vehicle's engine has a higher power output with less exhaust emissions.

Due to the design of the system, a conventional air flow meter cannot be used and a map sensor is often employed.

A complete single point injection unit.


Injectors - Single Point (Current) Diagnostics


The first part of the current signal is responsible for the electromagnetic force lifting the pintle. At this point the current can be seen to be maintained before dropping to zero as the pintle closes. With this in mind it can be seen that the amount of time that the injector is held open is not necessarily the same as the time measured. It is not however possible to calculate the time taken for the injectors spring to fully close the injector and cut off the fuel flow.

This test is ideal for identifying an injector with an unacceptably slow solenoid reaction time. Such an injector would not deliver the required amount of fuel causing the engine to run lean and consequently the lambda sensor voltage will be effected.

Technical Information

The reason that a single point injector is used rather than a multi-point configuration is sometimes hard to justify, and can only be due to a consideration towards costing and ease of application. A single injector is used (on larger engines two injectors can be used) in what may appear to be a carburettor housing.

It has a very low operating pressure (usually around 1 bar) and the atomising of the fuel can only be described as minimal, relying on the air movement within the inlet manifold to break the fuel down into smaller particles, ready for combustion.


Due to its design the main advantage over a carburettor is that a lambda sensor can be employed ensuring that closed loop control is maintained. Multi-point will undoubtedly ensure that the vehicle's engine has a higher power output with less exhaust emissions.

Due to the design of the system, a conventional air flow meter cannot be used and a map sensor is often employed.

A complete single point injection unit


Injectors - Multi-point (Voltage) Diagnostics

The injector is an electromechanical device which is fed by a 12 volt supply. The voltage will only be present when the engine is cranking or running, due to the voltage supply being controlled by a tachometric relay.

The length of time the injector is held open will depend on the input signals seen by the Electronic Control Module (ECM) from its various engine sensors.

The held open time or 'injector duration' will vary to compensate for cold engine starting and warm-up periods. The duration time will also expand under acceleration. The injector will have a constant voltage supply while the engine is running and the earth path will be switched via the ECM, the result can be seen in the example waveform. When the earth is removed a voltage is induced into the injector and a spike approaching 50 volts is recorded.

Multi-point injection may be either sequential or simultaneous. A simultaneous system will fire all 4 injectors at the same time with each cylinder receiving 2 injection pulses per cycle (720° crankshaft rotation). A sequential system will receiving just 1 injection pulse per cycle, this is timed to coincide with the opening of the inlet valve.

As a very rough guide the injector duration for an engine at normal operating temperature, at idle speed are:




2.5 ms - Simultaneous
3.5 ms - Sequential

Technical Information

The injector is supplied with fuel from a common fuel rail. The length of time that the injector is held open for will depend on the input signals seen by the engine management ECM from its various engine sensors.

These input signals will include :

The resistance of the coolant temperature.

The output voltage from the airflow meter (when fitted).

The resistance of the air temperature sensor.

The signal from the Manifold Absolute Pressure (MAP) sensor (when fitted).

The position of the throttle switch / potentiometer.

The held open time or injector duration will vary to compensate for cold engine starting and warm-up periods, i.e. a large duration that decreases the injection time as the engine warms to operating temperature.

The duration time will also expand under acceleration and contract under light load conditions.




Depending on the system encountered the injectors can fire either once or twice per cycle. The injectors are wired in parallel with simultaneous injection and will all fire together at the same time.

Sequential injection, as with simultaneous, has a common supply to each injector but unlike simultaneous has a separate earth path for each injector.




This individual firing allows the system, when used in conjunction with a phase sensor, to deliver the fuel when the inlet valve is open and the incoming air helps to atomise the fuel.

It is also common for injectors to be fired in 'banks' on 'V' configured engines.




The fuel will be delivered to each bank alternately. In the case of a Jaguar V12 the injectors are fired in 4 groups of 3 injectors.

Because of the frequency of the firing of the injectors, it is expected that a sequential injector will have twice the duration, or opening, than that of a simultaneous pulse. This will however be determined by the injector flow rate.

The injector consists of a solenoid operated valve which is held in the closed position by a spring until the earth circuit is completed by the ECM. When the electromagnetic field lifts the pintle off its seat, fuel is delivered to the engine. The total lift on the pintle is approximately 0.15 mm (6 thou) and has a reaction time around 1 millisecond.




A cross section of an electronic fuel injection.


An electronic fuel injector.


Injectors - Multi-Point (current) Diagnostics


Injector current is 'split' into two easily defied areas. The first is responsible for the electromagnetic force lifting the pintle, time taken is approximately 0.6 ms. At this point the current can be seen to fall before rising again as the pintle is held open. With this in mind it can be seen that the amount of time that the injector is held open is not necessarily the same as the time measured. It is not however possible to calculate the time taken for the injectors spring to fully close the injector and cut off the fuel flow.

This test is ideal for identifying an injector with an unacceptably slow solenoid reaction time. Such an injector would not deliver the required amount of fuel and the cylinder in question would run lean.

Technical Information

The multi-point injector is an electromechanical device which is fed by a 12 volt supply from either the fuel injection relay or from the Electronic Control Module (ECM).

The voltage in both cases will only be present when the engine is cranking or running, due to both voltage supplies being controlled by a tachometric relay.

The injector is supplied with fuel from a common fuel rail. The length of time that the injector is held open for will depend on the input signals seen by the engine management ECM from its various engine sensors.

These input signals will include :-

The resistance of the coolant temperature.

The output voltage from the airflow meter (when fitted).

The resistance of the air temperature sensor.

The signal from the Manifold Absolute Pressure (MAP) sensor (when fitted).

The position of the throttle switch / potentiometer.

The held open time or injector duration will vary to compensate for cold engine starting and warm-up periods, i.e. a large duration that decreases the injection time as the engine warms to operating temperature.

The duration time will also expand under acceleration and contract under light load conditions.




Depending on the system encountered the injectors can fire either once or twice per cycle.

The injectors are wired in parallel with simultaneous injection and will all fire together at the same time.




Sequential injection, as with simultaneous, has a common supply to each injector but unlike simultaneous has a separate earth path for each injector.

This individual firing allows the system, when used in conjunction with a phase sensor, to deliver the fuel when the inlet valve is open and the incoming air helps to atomise the fuel.




It is also common for injectors to be fired in 'banks' on 'V' configured engines. The fuel will be delivered to each bank alternately. In the case of a Jaguar V12 the injectors are fired in 4 groups of 3 injectors.

Because of the frequency of the firing of the injectors, it is expected that a sequential injector will have twice the duration, or opening, than that of a simultaneous pulse. This will however be determined by the injector flow rate.

The injector consists of a solenoid operated valve which is held in the closed position by a spring until the earth circuit is completed by the ECM. When the electromagnetic field lifts the pintle off its seat, fuel is delivered to the engine. The total lift on the pintle is approximately 0.15 mm (6 thou) and has a reaction time around 1 millisecond.




A cross section of an electronic fuel injection.


An electronic fuel injector.


Injectors - Bosch Common Rail Diesel (Current) Diagnostics


There are two distinctive points of injection, the first being the 'pre injection' phase, with the second pulse being the 'main' injection phase.

As the throttle is opened and the engine is accelerated, it can be seen in the second phase that the 'main' injection pulse expands in a similar way to a petrol injector.

In the third phase the throttle is released and the 'main' injection pulse disappears until such time as the engine returns to just above idle.

Under certain engine conditions a fourth phase may be seen, this is called the 'post injection' phase and is predominantly concerned with controlling the exhaust emissions.

Technical Information

The amount of fuel that is injected into the engine will be finely calculated by the vehicle's Electronic Control Module (ECM) from information received from the engines various sensors. The length of time that the injector is held open will also be determined by the fuel pressure.

The pump will at a lower engine speed deliver a lower pressure and therefore a longer duration will be required. As the engine / pump speed increases the injector duration will decrease but due to the higher pressure a greater quantity of diesel will be delivered to the engine.

The point of injection will in fact determine the injection timing, this will be determined by many factors including: engine speed, engine load & engine temperature. The injector is initially supplied with 80v to lift the injectors pintle and a 50v supply to hold the pintle open. These higher voltages are supplied from a capacitor which collects the induced voltage from the previous injection within the cycle. Unlike conventional diesel injection systems which only utilise a single injection period, the HDI system can have up to three!

Pre-injection is used to inject a small amount of fuel into the engine which immediately combusts and is used as the ignition source for the 'main' injection period. This type of two stage injection will reduce the characteristic diesel 'knock'.

Main injection is the conventional period of injection whose duration will be determined by the vehicle's ECM.

Post injection is used under certain engine conditions to reduce the amount of pollutants emitted from the vehicles exhaust system.

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