Re: i have a 4 cylinder with 8 spark plugs?????
This has been raised and answered before on this forum .Some answers on subject ,
Ford was trying to get more power and better fuel efficiency out of a smaller displacement engine. So to clean up emissions they used a dual spark plug producing a cleaner and more efficient burn.
Some engines (including many 2.3L Mustangs) use two plugs per cylinder to make sure that the cylinder fires off optimally. Usually this is because the head is designed such that it is impossible to put a single plug in the best spot so you place it off-center and put another plug in the "dead-spot" on the other side.
It was done for emissions. Nissan has used dual plugs on 4cyl engines since '84. It is to ignite the wasted gasses before they leave the engine.
Actually the 2nd plug fires at the same time as the 1st. It simply ensures more complete combustion during the power stroke. There is a waste spark that does "fire" during the exhaust stroke, but its effect on power or emissions is minimal at best.
Etc .etc Hope this explains and helps .