![]() This is a drive me to a garage limp mode. ![]() For example in a Ford V8 engine with coil on plug, if the camshaft position sensor stops working the engine will use only the crankshaft position sensor and regress to using waste spark and firing the injectors in banks instead of sequentially. Even with the fact that they are so modern these systems still retain some the the roots of where they came from. It's a more advantageous system because dwell and timing can be controlled per individual cylinder. Most automotive manufacturers did eventually go to individual coils per cylinder, this is called coil on plug or coil near plug. In reality the spark plug that is firing backwards (side electrode to center electrode) incurres the most wear. The wear and tear on the spark plugs you mention is over exaggerated because the waste plug always fires in the exhaust stream which is full of hot ionized gas that is really easy to fire through. These modules performed some of the needed calculations to relieve the PCM from having to do them. This is further evident from the use of ignition modules like in GM vehicles and EDIS in Ford vehicles. The injectors were fired all together like one big injector unlike sequential fuel injection that followed that fired the injectors individually in the firing order. This is evident from the fact that at the same time multi point fuel injection systems were all the rage. Automotive computers were in their infancy at the time and just couldn't crunch the numbers to fire a set of individual coils. The biggest reason for waste spark is that it required less computational power. It was an excellent replacement for a distributor but ultimately it was a compromise. When waste spark first came out it was on the cutting edge. The spark in the cylinder with exhaust is called the waste spark. When the coil fires, both spark plugs spark at the same time, one in the cylinder with fuel and the other in the cylinder with exhaust. This puts one cylinder in the compression stroke and the other in the exhaust stroke at the same time. These spark plugs reside in two opposing cylinders, meaning the pistons move up and down at the same time. Each ignition coil is hooked up to two spark plugs. In a waste spark system an ignition coil has two spark plug outputs unlike every other system only having one. ![]() ![]() The answer to this question is more historical than anything else but first a little background. I'm sorry if this ends up being a lengthy answer. I'm sure the space and cost considerations answers the question, but I was hoping for some other thoughts on the advantages/disadvantages of a system that avoids the wasted spark.īonus question: Do two-cylinder engines typically spark both cylinders at the same time? Or do they tend to spark separately?īonus question 2: Is there a wasted spark in engines with an odd number of cylinders? I wouldn't think so. ![]() This would half the number of sparks on each plug since they could be set to only fire on a compression stroke. My question: Why not double the number of coil packs to avoid the wasted spark? Though this would take up more space and cost more for the packs, surly it would reduce wear and tear on the spark plugs to some extent as well as the spark plug wires and perhaps the alternator. However, they don't take up much space and don't cost that much (at least for my 4-cyl car). It also saves money on initial purchase and replacement. I understand this is probably done to save space under the hood since it would double the number of required coil packs. This means there is a wasted spark as one cylinder is in exhaust, while the other actually fires at the top of compression. In a typical four-stroke engine with an even number of cylinders, spark plugs fire in pairs. ![]()
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