Ignition Waveforms... This is a super tough proposition.

Reading ignition waveforms has often been considered a thing of the past, difficult or plain impossible by newer techs coming to the field. However, the need for such knowledge is the difference between fixing it right or throwing parts at the vehicle. Get the scoop here...

 

THEORY OF OPERATION

IGNITION ANALYZER QUICK CHECKLIST

NOTE: Always pre-load the vehicle during testing. Most faults (lean condition, valve problems, ignition components, density, etc.) will only show up on WOT-snap, pre-load or 2500 RPM testing.

These steps can be used with any ignition scope/analyzer. It’s important to follow the sequence presented here.

TESTING SEQUENCE

1. PARADE PATERN – Good for fixed resistance checks (spark plugs, ignition wires, cap & rotor). This setting is also helpful for a preliminary spark duration analysis (mixture & density condition). Settings on PARADE should be at 2 to 5 KVs-Div & 5mS-Div.

2. BAR GRAPH (Firing line) – Indicates firing line KVs. This test is very useful when used with the snap-WOT procedure to do an electronic compression test.

3. SUPERIMPOSED – Useful for spark line analysis which indicate spark plug gap condition. Settings should be at 2 KVs-Div & 0.5 to 0.2mS-Div.

4. RASTER PATERN – Used for spark duration comparison among all cylinders. Settings should be at 2 KVs-Div & 0.2 mS-Div, so as to widen the spark duration to a maximum. This will show fast happening and intermittent misfires (lean, rich or density).

5. SINGLE CYLINDER – Good for final analysis to pin-point variable resistance (mixture & density) problems. Settings at 2KVs-Div and 0.2 to 0.5 mS-Div.

An idle baseline should be taken at first, followed by snap-WOT, 2500 RPM and pre-loading as necessary. These five easy steps should point you in the right direction.

IGNITION COIL CURRENT WAVEFORM INTERPRETATION

THEORY OF OPERATION

The following is a brief explanation of how to interpret ignition coil current waveforms.

NOTEAny low resistance or short in the primary circuit will lead to a rapid raise in current buildup and therefore will result in a low Kv output by the coil. The current release must be vertical (falling edge) or fast so as to collapse the magnetic field fast enough and induce the proper amount of Kvolts on the secondary circuit.

As a rule, secondary ignition problems (plugs, ign. wires, cap, rotor, etc) do not show up on a current waveform. However, a current waveform is instrumental in detecting a defective coil without any complicated or intrusive electrical hookups.

By analyzing the above signal waveform a quick determination can be made as to the electrical condition of the coil. It is important to know that current or amperage is the best indicator of the general working condition of any electronic circuit. If the circuit can not draw the working current load it should be considered defective. Always perform all the current measurements while loading the engine’s ignition system. A 2500 RPM and/or a pre-loaded test is the best way to stress the ignition system. The higher the combustion chamber pressure the higher the K volts needed to ignite the air/fuel mixture. Most ignition problems will not show up on an idling engine.

Ignition coils are supposed to charge up to full saturation in a timely manner. This means that the current waveform has to be at an angle, indicating a slowly expanding magnetic field up to full saturation.

The procedures to analyze an ignition coil should be used in conjunction with a general ignition system analysis. These procedures are dissected and presented here for sake of clarity. In no way can it replace the final manual engine analyzer test. Ignition coil current tests should be used in combination with other tests to arrive at the final diagnostic decision.

 

 

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