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Secondary - Distributorless System - Positive Fired Diagnostics
(scroll for Negative, King and Plug)

When the positive fired plug kV's are recorded on Distributorless Ignition Systems (DIS), the voltage seen on the waveform should be in the 'upright position' and not inverted as this would suggest that the inappropriate lead has been chosen.

The plug voltage while the engine is running, is continuously fluctuating and the display will be seen to move up and down. Snap the throttle and observe the voltage requirements when the engine is under load. This is the only time that the plugs are placed under any strain and is a fair assessment of how they will perform on the road.

The second part can be seen running at approximately 3 kV, this is known as the sparkline voltage.


This second voltage is the voltage required to keep the plug running after it's initial spark to jump the gap. This voltage will be proportional to the resistance within the secondary circuit. The length of the line can be seen to run for approximately 1.4ms. This is the spark duration, the length of time the spark is flowing across the plugs gap.

It is worth remembering that a positive fired spark plug will require a greater voltage to fire it than a negative fired plug. This due to electron flow when the metal surface of the plug gets hot and is known to 'boil away' negative electrons. This process is referred to as thermionic emissions. This can be seen as greater wear on the plugs electrode than for a negative fired plug.
Technical Information

Situated within the coil's primary winding is the secondary winding. This winding 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 High Tension (HT) voltage is produced by mutual induction between the primary winding and the secondary winding, the central soft iron core intensifies the magnetic field between them.

On a distributor system, the secondary HT voltage produced by the coil is allocated to the appropriate spark plug via the contacts inside the distributor cap.

The voltage measured at the spark plug is the voltage required to jump the plug gap in varying conditions, this voltage will be determined by any of the following :-

 
The plug kV's will be increased by:- The plug kV's will be decreased by:-
Large plug gaps Small plug gaps
A large rotor air gap Low compression
A break in a plug lead Rich mixture
A break in the king lead Incorrect ignition timing
Worn spark plugs Tracking to earth
A lean mixture Fouled plugs
  Rotor to reluctor misalignment

The plug Kilo Volt (kV) requirement of older engines tend to be lower than that of the modern engine, as the later designs will run higher compression ratios, leaner Air/Fuel ratios and have larger spark plug gaps.

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 eliminated from the system. Reliability problems from dampness and tracking is now almost eliminated.

DIS has it's 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 will have the effect of pronounced plug wear on the positive fired plugs.


This system, because of its nature, will fire the plugs each revolution, instead of every other, and is known as a wasted spark system. This does not mean that the plugs will wear at twice the normal 0rate, as the wasted spark is on the exhaust stroke, and is therefore under no compression. If the spark plugs are removed after several thousand miles and examined, it will show that two of the plugs have relatively square electrodes, while the plugs that have been fired positive will have pronounced plug wear.

An example wasted spark coil pack.


Secondary - Distributorless System - Negative Diagnostics


When the plug kV's are recorded on a DIS or coil per cylinder ignition system, the voltage should be in the 'upright position' and not inverted as this would suggest that either the wrong polarity has been selected or in the case of DIS, the inappropriate lead has been chosen. The plug voltage while the engine is running, is continuously fluctuating.

Snap the throttle and observe the voltage requirements when the engine is under load. This is the only time that the plugs are placed under any strain and is a fair assessment of how they will perform on the road.

This second voltage is the voltage required to keep the plug running after its initial spark to jump the gap. This voltage will be proportional to the resistance within the secondary circuit. The length of the line can be seen to run for approximately 1.4ms. This is the spark duration, the length of time the spark is flowing across the plugs gap.

Technical Information

Situated within the coil's primary winding is the secondary winding. This winding 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 High Tension (HT) voltage is produced by mutual induction between the primary winding and the secondary winding, the central soft iron core intensifies the magnetic field between them.

On a distributor system, the secondary HT voltage produced by the coil is allocated to the appropriate spark plug via the contacts inside the distributor cap.

The voltage measured at the spark plug is the voltage required to jump the plug gap in varying conditions.




Secondary - Distributor System King Diagnostics

The secondary waveform shows the length of time that the HT is flowing across the spark plugs electrode after its initial voltage to jump the plug gap. This time is referred to as either the 'burn time' or the 'spark duration'.
In the illustration shown it can be seen that the horizontal voltage line in the centre of the oscilloscope is at fairly constant voltage of approximately 4 Kilo volts (kV), which then drops sharply into what is referred to as the 'coil oscillation' period. The 'burn time' is also illustrated
The coil oscillation period should display a minimum number of peaks (both upper and lower) and a minimum of 4 - 5 should be seen.

A loss of peaks indicates that the coil needs substituting. The period between the coil oscillation and the next 'drop down' is when the coil is at rest and there is no voltage in the coil' s secondary circuit. The 'drop down' is referred to as the 'polarity peak', (as illustrated below, and produces a small oscillation in the opposite direction to the plug firing voltage.


This is due to the initial switching on of the coil's primary current. The voltage within the coil is only released at the correct point of ignition and the HT spark ignites the Air/Fuel mixture.
The plug firing voltage is the voltage required to jump and bridge the gap at the plug's electrode, commonly known as the 'plug kV'. This is shown here, in this example the plug kV is 13.5 kV.
Technical Information

Situated within the coil's primary winding is the secondary winding. This winding 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 High Tension (HT) voltage is produced by mutual induction between the primary winding and the secondary winding, the central soft iron core intensifies the magnetic field between them.

On a distributor system, the secondary HT voltage produced by the coil is allocated to the appropriate spark plug via the contacts inside the distributor cap.

The voltage measured at the spark plug is the voltage required to jump the plug gap in varying conditions, this voltage will be determined by any of the following :-


The plug kV's will be increased by:- The plug kV's will be decreased by:-
Large plug gaps Small plug gaps
A large rotor air gap Low compression
A break in a plug lead Rich mixture
A break in the king lead Incorrect ignition timing
Worn spark plugs Tracking to earth
A lean mixture Fouled plugs
  Rotor to reluctor misalignment

The plug Kilo Volt (kV) requirement of older engines tend to be lower than that of the modern engine, as the later designs will run higher compression ratios, leaner Air/Fuel ratios and have larger spark plug gaps.

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 eliminated from the system. Reliability problems from dampness and tracking is now almost eliminated.

DIS has it's 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 will have the effect of pronounced plug wear on the positive fired plugs.


This system, because of its nature, will fire the plugs each revolution, instead of every other, and is known as a wasted spark system. This does not mean that the plugs will wear at twice the normal rate, as the wasted spark is on the exhaust stroke, and is therefore under no compression. If the spark plugs are removed after several thousand miles and examined, it will show that two of the plugs have relatively square electrodes, while the plugs that have been fired positive will have pronounced plug wear.

An example coil.



Secondary - Ignition Diagnostics

The secondary waveform shows the length of time that the HT is flowing across the spark plugs electrode after its initial voltage to jump the plug gap. This time is referred to as either the 'burn time' or the 'spark duration'. In the illustration shown it can be seen that the horizontal voltage line in the centre of the oscilloscope is at fairly constant voltage of approximately 4 Kilo volts (kV), which then drops sharply into what is referred to as the 'coil oscillation' period. The 'burn time' is also illustrated here
The coil oscillation period should display a minimum number of peaks (both upper and lower) and a minimum of 4 - 5 should be seen.
A loss of peaks indicates that the coil needs substituting. The period between the coil oscillation and the next 'drop down' is when the coil is at rest and there is no voltage in the coil' s secondary circuit. The 'drop down' is referred to as the 'polarity peak' and produces a small oscillation in the opposite direction to the plug firing voltage.
This is due to the initial switching on of the coil's primary current. The voltage within the coil is only released at the correct point of ignition and the HT spark ignites the Air/Fuel mixture.
The plug firing voltage is the voltage required to jump and bridge the gap at the plug's electrode, commonly known as the 'plug kV'. This is shown here, in this example the plug kV is 13.5 kV.
Technical Information

Situated within the coil's primary winding is the secondary winding. This winding 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 High Tension (HT) voltage is produced by mutual induction between the primary winding and the secondary winding, the central soft iron core intensifies the magnetic field between them.

On a distributor system, the secondary HT voltage produced by the coil is allocated to the appropriate spark plug via the contacts inside the distributor cap.

The voltage measured at the spark plug is the voltage required to jump the plug gap in varying conditions, this voltage will be determined by any of the following :-


The plug kV's will be increased by:- The plug kV's will be decreased by:-
Large plug gaps Small plug gaps
A large rotor air gap Low compression
A break in a plug lead Rich mixture
A break in the king lead Incorrect ignition timing
Worn spark plugs Tracking to earth
A lean mixture Fouled plugs
  Rotor to reluctor misalignment 

The plug Kilo Volt (kV) requirement of older engines tend to be lower than that of the modern engine, as the later designs will run higher compression ratios, leaner Air/Fuel ratios and have larger spark plug gaps.

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 eliminated from the system. Reliability problems from dampness and tracking is now almost eliminated.

DIS has it's 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 will have the effect of pronounced plug wear on the positive fired plugs.

This system, because of its nature, will fire the plugs each revolution, instead of every other, and is known as a wasted spark system. This does not mean that the plugs will wear at twice the normal rate, as the wasted spark is on the exhaust stroke, and is therefore under no compression. If the spark plugs are removed after several thousand miles and examined, it will show that two of the plugs have relatively square electrodes, while the plugs that have been fired positive will have pronounced plug wear.