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.
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
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.
NOTE: Any 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
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