Vauxhall Workshop Service and Repair Manuals

Ignition, Secondary (STD Single)  

Measurement:	Plot of the ignition voltage for one cylinder when the engine is idling (single display).
Check Objective:	Determining ignition faults by analysing the ignition voltage plot for each of the cylinders.

Preparation  

Caution - high voltage! Observe safety advice! Engine oil temperature > 80 ° C.

Connections  

INPUT A	COM/TRIGGER
Clamp secondary measurement sensor across the ignition lead of the cylinder under test. Connect ground connection to ground.

Procedure  

Start the engine and allow it to idle.  

 

Reference Curve     Notice:  Positive and negative ignition voltages occur on twin spark ignition coils systems. This can be easily recognised, as the ignition voltage spike for the negative polarity cylinders points downwards.   If this occurs, the ignition voltage graph can be turned by depressing the (F2) key.   Because only relatively large deviations of the individual ignition voltages patterns can be detected when using the single display, the measured voltage plots should also be compared against one another (examination of stored graphs).   The evaluation mainly considers the ignition voltage spike and the combustion voltage plot. The horizontal scaling factor can be set up to 500 μ s/DIV in order to permit better display of the ignition voltage plot. Depress the [ms] key twice, then move the trigger plot to the left by pressing [F5] and the [left arrow] key until the entire combustion voltage plot is clearly visible again.

 

Fault Diagram 1   Symptoms:   The ignition voltage for one cylinder is too low and the combustion voltage plot is considerably longer than for that of the other cylinders.

Possible Causes	Countermeasures
Spark plug electrode gap too small.	Check and correct electrode gap or replace spark plugs.
The affected cylinder has insufficient compression.	Perform compression test (see section 3.4).

Notice: 

On 4-valve engines the mixture swirl within the combustion chamber is so intense that the combustion voltage plot behaves very erratically and as a result this does not necessarily indicate soiling of the spark plugs on these engines.  

 

Fault Diagram 2   Symptoms:   The ignition voltage for one cylinder is too high and the combustion voltage plot is consistently shorter than those of the other cylinders.   The combustion voltage plot sometimes disappears completely and ignition voltage spikes are sometimes very large.

Possible Causes	Countermeasures
Spark plug electrode gap is too large.	Check and correct electrode gap or replace spark plugs.
If the combustion voltage plot sometimes disappears completely and the ignition voltage spikes are sometimes very large, there may be an open-circuit in the ignition lead.	Use a multimeter (resistance measurement) to check the ignition lead of the affected cylinder.
	Max. Resistance: 12 kilohm (for copper leads, only the resistance stamped on the spark plug socket is valid). If this value is exceeded, the ignition lead must be replaced.

Notice: 

On 4-valve engines the mixture swirl within the combustion chamber is so intense that the combustion voltage plot behaves very erratically and as a result this does not necessarily indicate soiling of the spark plugs on these engines.  

 

Fault Diagram 3   Symptoms:   The combustion voltage plot is too short and the oscillation at the end of the combustion voltage plot is missing.

Possible Causes	Countermeasures
If the fault occurs on all of the cylinders which form one secondary circuit, this indicates an open-circuit in the secondary winding of the affected ignition coil (booster gap).	Use a multimeter (resistance measurement) to check the secondary winding of the ignition coil for open-circuit. If the instrument displays "OL" (infinite resistance), the ignition coil must be replaced.
If the fault is only detected on one cylinder, there is an open-circuit in the ignition lead of the corresponding cylinder.	Check the ignition leads and the spark plug sockets of the affected circuit for open-circuit (see above).

 

Fault Diagram 4   Symptoms:   The ignition voltage spike and the combustion voltage plot for one cylinder are lower than those of the other cylinders and the engine misfires.

Possible Causes	Countermeasures
Faulty high voltage insulation	Check the insulation of the ignition leads and spark plugs for cracks and replace if necessary.   If the misfiring continues, the ignition coil must be replaced.

 

Fault Diagram 5   Symptoms:   The start of the combustion voltage plot is too high and then falls sharply.   The engine mainly misfires under acceleration

Possible Causes	Countermeasures
If the fault occurs on all of the cylinders which form one ignition circuit: The ignition lead is faulty.	Use a multimeter (resistance measurement) to check the ignition leads of the affected cylinder.   Max. Resistance: 12 kilohm (only the resistance stamped on the spark plug socket is valid for copper leads). If this value is exceeded, the corresponding ignition lead must be replaced.

 

Fault Diagram 6   Symptoms:   The oscillations in the closing phase and after the combustion voltage plot for all of the cylinders are heavily attenuated or even missing.

Possible Causes	Countermeasures
Faulty primary winding in the ignition coil	Use a multimeter (resistance measurement) to check the primary winding of the ignition coil.   Resistance Value approx. 0.3 - 0.7 ohm

 

Fault Diagram 7   Symptoms:   The start point of the combustion voltage plot jumps and the combustion voltage plot sometimes falls sharply.

Possible Causes	Countermeasures
Heavy soiling of the spark plug.	Clean and recheck spark plug.

 

Fault Diagram 8   Symptoms:   Combustion voltage plot is missing completely.

Possible Causes	Countermeasures
Faulty ignition coil.	Replace ignition coil.

 

Fault Diagram 9   Symptoms:   The start of the decay phase is considerably greater than the ignition voltage spike.

Possible Causes	Countermeasures
Mixture in the affected cylinder is too lean (not for fuel injection systems).	Check the injector.
Insufficient compression	Perform compression test or pressure loss test.

Notice: 

If the fault occurs on all of the cylinders, check the intake side for unmetered air.