![]() ![]() When a coil pack is used, it fires differently than a conventional ignition in terms of polarity. This style ignition system allows for longer arcing time of the spark plug when measured in degrees of crankshaft rotation past top dead center. ![]() The control unit is programmed with the correct firing order. When an engine has no distributor, it will use a sensor on the crankshaft to identify each firing event the sensor also recognizes the number-one cylinder. Many modern gasoline engines do not employ a traditional distributor but, instead, have either a coil on each spark plug or a coil pack that fires two cylinders. Then the wire from either the breaker points or the ignition module goes to coil (-). The proper connection for a coil is that the voltage from the ignition switch goes to coil (+). Most times, the engine would idle fine, but as soon as any load was applied, it would misfire. If the primary leads to the coil were accidently connected in reverse, the amount of energy the coil could produce would be greatly diminished. That side electrode is grounded via the plug threads to the cylinder head. ![]() The demand on the ignition will increase, and the energy will look for an easier path.Ī spark plug on most engines fires from the center electrode to the side electrode. Once the flame expands away from that region, it dies out, and the cylinder is no longer contributing any power. In most instances, the flame does begin since the air-fuel mixture by design is concentrated around the spark plug electrode. When the mixture is lean, the flame cannot expand across the cylinder bore since it requires both fuel and oxygen to accomplish this. If the mixture is excessively lean, the engine will misfire since the fuel molecules in the intake air are too far apart. The engine will be weak, the unburned fuel will foul the spark plug, and the exhaust will pop. When this occurs, that cylinder will not be contributing full power to the crankshaft. If it is easier to go to ground through the insulation on the ignition wire instead of arcing the gap of the plug under high cylinder pressure, it will. It will always take the path of least resistance. To diagnose a performance issue expediently, you need to remember that electrical demand is linked to load.Īn engine is considered to misfire when there is not enough electrical energy going to the spark plug to keep it arcing or there is a path- way in the engine for the energy to take that bypasses the plug’s electrodes. In like fashion, during throttle movement (transient operation), ignition demand spikes just as the throttle plate is evoked. Due to this, the engine may run fine under a given operating state and then buck, pop, and misfire when faced with different operating conditions. If the engine was still idled and a load was gently applied (engaging a PTO, for example), the voltage required to arc the plug would increase dramatically. This is due to the throttle being almost closed, the engine rpm being low, and the fact that there is no load on the engine. Cylinder pressure and ignition demand are constantly changing with engine load.Īt idle, the required energy to arc the spark plug is very low since the cylinder pressure is minimal. Compression ratio is a design function of the difference in the volume of the bore with the piston at bottom dead center, compared to when it is at top dead center. Cylinder pressure is the cumulative result of the load on the engine in relation to the volumetric efficiency and mixture strength.
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