Coil on Plug (COP) vs Ignition Coil
- Thread starter hpman247
- Start date
oddball
Dedicated LVC Member
A traditional coil is one coil that fires more than one spark plug. It must be somewhat large and has to be cycled quite fast.
A coil pack is multiple coils - typically one for each spark plug handled by the pack - packaged into a single unit. e.g., there would be one pack for each side of the engine, with four coils inside it.
A coil-on-plug is a small coil that fires just one spark plug. It's called a COP because it's typically mounted on top of the spark plug, instead of remotely mounted like days of yore. GM's LS engines also use COPs, but they look more like a traditional coil and are mounted to the valve cover.
Having separate coils is good because they cycle much slower - more recharge time = cheaper construction and/or more spark - and can be much smaller.
Every gas engine uses coils to generate the spark (or magnetos, but let's not go there). Whether it's a single coil, packs, or COPs is up to the manufacturer and the packaging constraints.
A coil pack is multiple coils - typically one for each spark plug handled by the pack - packaged into a single unit. e.g., there would be one pack for each side of the engine, with four coils inside it.
A coil-on-plug is a small coil that fires just one spark plug. It's called a COP because it's typically mounted on top of the spark plug, instead of remotely mounted like days of yore. GM's LS engines also use COPs, but they look more like a traditional coil and are mounted to the valve cover.
Having separate coils is good because they cycle much slower - more recharge time = cheaper construction and/or more spark - and can be much smaller.
Every gas engine uses coils to generate the spark (or magnetos, but let's not go there). Whether it's a single coil, packs, or COPs is up to the manufacturer and the packaging constraints.
joegr
Dedicated LVC Member
Good description, but...
Most coil packs that I have seen have one coil for each pair of spark plugs. (You have to cut them open to tell that there are half as many coils as you would expect in there.) For example, my 2001 Ranger uses a coil pack with three coils. The three coils fire all six spark plugs. The 94 Grand Marquis that I had used two coil packs, each with two coils. Each two coil pack fired four spark plugs. The plugs are paired such that while one of the pair is firing on the compression stroke, the other one is firing on the exhaust stroke. That spark is wasted, but does no harm. The advantage to the system is that it takes less control electronics.
There is another advantage to using COPs. Since they don't have long wires (just a short boot), the stray capacitance on the secondary side can be very well accounted for. This means that ignition timing can be more precise. That helps with emissions and mileage. Every little bit counts.
Most coil packs that I have seen have one coil for each pair of spark plugs. (You have to cut them open to tell that there are half as many coils as you would expect in there.) For example, my 2001 Ranger uses a coil pack with three coils. The three coils fire all six spark plugs. The 94 Grand Marquis that I had used two coil packs, each with two coils. Each two coil pack fired four spark plugs. The plugs are paired such that while one of the pair is firing on the compression stroke, the other one is firing on the exhaust stroke. That spark is wasted, but does no harm. The advantage to the system is that it takes less control electronics.
There is another advantage to using COPs. Since they don't have long wires (just a short boot), the stray capacitance on the secondary side can be very well accounted for. This means that ignition timing can be more precise. That helps with emissions and mileage. Every little bit counts.
The wasted spark also helps with emissions by causing a second burn of any unspent fuel in the exhaust stroke. But that's more of a fortunate side-effect for the manufacturers. It was really about simplified electronics and limited control systems.
