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Cross Firing Cylinders

All V8s have two end cylinders on one bank which fire consecutively.   They won't cross fire if the plug wires are reasonably new and not routed parallel to one another.   Put the wires for cylinders 7 and 8 on the two outside edges of the wire loom and all will be OK.

Electricity is very lazy and wants to go to ground the easiest way possible.   When a cylinder is at the top of the compression stroke the gases are very dense and actually oppose the spark significantly more than in normal density air.

When wires run parallel for a distance an electrical signal may be induced or transferred into the other wire especially when the signal is a series of strong pulses.   This is known as magnetic induction.

The firing order has cylinder 7 firing just before cylinder 8.   Thus when 7 is about to fire then 8 is 90 degrees from firing.   The compressed mixture in 7 resists the spark from jumping across the plug to ground. So the spark in the wire to cylinder 7 is looking for a easy path to ground.  And 8 is at a much lower pressure as it is in the middle of is compression stroke.   If the wires are not in good condition and if the wires are running in parallel for any distance, the spark will jump to the number 8 wire and cause a misfire in 7 and fire 8 early.

When 8 is ready to fire 7 is in the middle of combustion with extremely high pressure so cross firing to 7 is unlikely.