usually nothing. no warning except maybe a miss in the engine. if you have 2 spark plugs per coil pack, then one or both plugs do not fire and you will have a very noticeable miss and poor acceleration. engine may not run at all. it would be my suggestion to replace ALL coil packs, spark plugs, and plug wires if 100,000 miles or over.
Then there is a no spark condition and engine will not run. If it has more than one coil pack it will miss on the cylinders controlled by the defective coil pack.
Most automobiles will not start with a nonfunctioning coil pack. The coil pack will cause the spark plugs not to fire.
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symptoms are: you can hear the engine missing, spitting and sputtering, loss of power...you can tell if it is a coil pack by unscrewing the spark plug that it connects to coil pack. when you look at your spark plug it should be a light grayish, white..this means the coil pack is working....it is best if you do this with new spark plugs, because your spark plugs could be bad. but you do this process until you find a bad plug then, that coil pack probably is the bad coil pack.
A bad coil pack would not smell like gasoline.
bad coil pack... replace coil pack
Bad coil or coil pack.
Go to AutoZone have them rear your codes for FREE. This way you will know which Coil Pack is goig bad / or is bad. If you have a 4.6L you will have only 2 Big Coil Packs. If you have the 5.4L you will have 8 Coil Packs , One coil pack for each cylinder.
auto zone will check your codes for FREE. if you have a bad coil pack they will tell you.
part of your coil pack could be bad or your ignition control module could be bad it just bolts right on top of your coil pack
bad spark wires
bad coil pack or bad wire