Yes...it could be causing your trouble. You remember your science classes I'm certain and you recall for a coil to work you actually must have 2 coils (which inside your coil you have that). A failing coil will very often have some shorted out windings. This causes reduced inductance and while you will still have enough oomph to make a spark, it will result in lower than normal energy coming from the coil. Another thing: heat changes things inside a coil. When a failing coil gets hot (from sitting on the side of the head) it can make problems worse...meaning those shorted out windings can get a bit closer together. HEI still uses a coil but the whole HEI scheme is "high energy" oriented and will produce a more powerful spark.
