AC Delco Coils Review
Senior Member
Joined: Jul 2004
Posts: 6,200
Likes: 39
From: Easton, Pa.
There is something to be said about replacing plugs at regular intervals.
The coils are designed to provide upwards of 40,000 volts at full discharge.
This is reserve output because normally the spark occurs across the electrodes in 10,000 +/- volt range depending on the mixture ratio and plug electrode conditions at the time of discharge.
As the plug gap and electrode condition degrade the spark level required rises.
At this point enter EGR operation. When EGR flow is called, the mixture goes very lean from exhaust pollution (not excessive air). At this time the coils are called on to fire this polluted mixture and calls on the coils reserve voltage to do so. Any coil who's reserve output has dropped too or below the required level to fire the polluted mixture will produce misfires until the EGR closes and voltage requirements have reduced..
Higher voltages from degraded plug electrodes could affect the coil life but detecting it in a practical manner would be difficult to do. Many tests over a long life periods would be required to begin to see a pattern to prove any reliable data on several different product mfgers.
When the PCM coil driver opens the coil circuit, the voltage buildup around the coil and it's core collapses and causes the high voltage to jump the plug electrode gap causing an intense spark that begins the flame travel across the cylinder head volume.
This field collapse re induces a voltage spike that can 'ring' as it subsides in amplitude.
This can also be responsible for internal flashover eventually causing a coil failure especially if the plugs have eroded excessively and dose not limit the high voltage to the lower more normal values in the 10k range.
A word about coil voltage limiting is the spark is a resistance path to ground and shunts the coil voltage. This is the limiting factor on coil voltage and causes the reserve to be there if the spark resistance rises in value.
From the above, one could see that replacing plugs at shorter intervals has the advantage of sharper running engine performance more of the time and even may use plugs of lower cost. The cost advantage may be lost in the greater replacement intervals but would be worth it in more consistent engine performance.
The OEM plugs specified are more for long life without changing as a service enhancement for the average owner. The greater cost is in their design using harder metal alloys that erode at a much slower rate over time.
A quality plug of the correct heat range, reach and hard or copper center electrode work just as well in the shorter intervals.
Good luck.
The coils are designed to provide upwards of 40,000 volts at full discharge.
This is reserve output because normally the spark occurs across the electrodes in 10,000 +/- volt range depending on the mixture ratio and plug electrode conditions at the time of discharge.
As the plug gap and electrode condition degrade the spark level required rises.
At this point enter EGR operation. When EGR flow is called, the mixture goes very lean from exhaust pollution (not excessive air). At this time the coils are called on to fire this polluted mixture and calls on the coils reserve voltage to do so. Any coil who's reserve output has dropped too or below the required level to fire the polluted mixture will produce misfires until the EGR closes and voltage requirements have reduced..
Higher voltages from degraded plug electrodes could affect the coil life but detecting it in a practical manner would be difficult to do. Many tests over a long life periods would be required to begin to see a pattern to prove any reliable data on several different product mfgers.
When the PCM coil driver opens the coil circuit, the voltage buildup around the coil and it's core collapses and causes the high voltage to jump the plug electrode gap causing an intense spark that begins the flame travel across the cylinder head volume.
This field collapse re induces a voltage spike that can 'ring' as it subsides in amplitude.
This can also be responsible for internal flashover eventually causing a coil failure especially if the plugs have eroded excessively and dose not limit the high voltage to the lower more normal values in the 10k range.
A word about coil voltage limiting is the spark is a resistance path to ground and shunts the coil voltage. This is the limiting factor on coil voltage and causes the reserve to be there if the spark resistance rises in value.
From the above, one could see that replacing plugs at shorter intervals has the advantage of sharper running engine performance more of the time and even may use plugs of lower cost. The cost advantage may be lost in the greater replacement intervals but would be worth it in more consistent engine performance.
The OEM plugs specified are more for long life without changing as a service enhancement for the average owner. The greater cost is in their design using harder metal alloys that erode at a much slower rate over time.
A quality plug of the correct heat range, reach and hard or copper center electrode work just as well in the shorter intervals.
Good luck.