We will see a low kilovolt because of low compression, directly followed by hash caused by air flow distorting the spark. Depending on frequency, the problem could be traced to worn valve guides, carbon deposits, weak valve spring or poor lubrication. Conclusive diagnosis depends on how many cylinders are affected and if the problem is intermittent or permanent. The value of a scope is apparent only when the potential is fully understood. Let us assume that every cylinder performed as it was designed. The air inhaled is determined by bore and stroke of the piston. This air is matched with a precise amount of fuel and the process of total combustion matches the coil output energy with very little residual energy to spare. All cylinders are created equal and should follow that precise pattern of combustion efficiency. Any deviation will affect the firing time and alter the residual coil energy. Because the lab scope is time based, there is no better tool to measure, compare and display combustion efficiency per cylinder.
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